libmdbx/src/mdbx.c

/*
 * Copyright 2015-2017 Leonid Yuriev <leo@yuriev.ru>
 * and other libmdbx authors: please see AUTHORS file.
 * All rights reserved.
 *
 * This code is derived from "LMDB engine" written by
 * Howard Chu (Symas Corporation), which itself derived from btree.c
 * written by Martin Hedenfalk.
 *
 * ---
 *
 * Portions Copyright 2011-2015 Howard Chu, Symas Corp. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted only as authorized by the OpenLDAP
 * Public License.
 *
 * A copy of this license is available in the file LICENSE in the
 * top-level directory of the distribution or, alternatively, at
 * <http://www.OpenLDAP.org/license.html>.
 *
 * ---
 *
 * Portions Copyright (c) 2009, 2010 Martin Hedenfalk <martin@bzero.se>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

#include "./bits.h"

/*----------------------------------------------------------------------------*/
/* rthc (tls keys and destructors) */

typedef struct rthc_entry_t {
  MDBX_reader *begin;
  MDBX_reader *end;
  mdbx_thread_key_t key;
} rthc_entry_t;

#if MDBX_DEBUG
#define RTHC_INITIAL_LIMIT 1
#else
#define RTHC_INITIAL_LIMIT 16
#endif

static unsigned rthc_count;
static unsigned rthc_limit = RTHC_INITIAL_LIMIT;
static rthc_entry_t rthc_table_static[RTHC_INITIAL_LIMIT];
static rthc_entry_t *rthc_table = rthc_table_static;

__cold void mdbx_rthc_dtor(void *ptr) {
  MDBX_reader *rthc = (MDBX_reader *)ptr;

  mdbx_rthc_lock();
  const mdbx_pid_t self_pid = mdbx_getpid();
  for (unsigned i = 0; i < rthc_count; ++i) {
    if (rthc >= rthc_table[i].begin && rthc < rthc_table[i].end) {
      if (rthc->mr_pid == self_pid) {
        rthc->mr_pid = 0;
        mdbx_coherent_barrier();
      }
      break;
    }
  }
  mdbx_rthc_unlock();
}

__cold void mdbx_rthc_cleanup(void) {
  mdbx_rthc_lock();
  const mdbx_pid_t self_pid = mdbx_getpid();
  for (unsigned i = 0; i < rthc_count; ++i) {
    mdbx_thread_key_t key = rthc_table[i].key;
    MDBX_reader *rthc = mdbx_thread_rthc_get(key);
    if (rthc) {
      mdbx_thread_rthc_set(key, NULL);
      if (rthc->mr_pid == self_pid) {
        rthc->mr_pid = 0;
        mdbx_coherent_barrier();
      }
    }
  }
  mdbx_rthc_unlock();
}

__cold int mdbx_rthc_alloc(mdbx_thread_key_t *key, MDBX_reader *begin,
                           MDBX_reader *end) {
#ifndef NDEBUG
  *key = (mdbx_thread_key_t)0xBADBADBAD;
#endif /* NDEBUG */
  int rc = mdbx_thread_key_create(key);
  if (rc != MDBX_SUCCESS)
    return rc;

  mdbx_rthc_lock();
  if (rthc_count == rthc_limit) {
    rthc_entry_t *new_table =
        realloc((rthc_table == rthc_table_static) ? NULL : rthc_table,
                sizeof(rthc_entry_t) * rthc_limit * 2);
    if (new_table == NULL) {
      rc = MDBX_ENOMEM;
      goto bailout;
    }
    if (rthc_table == rthc_table_static)
      memcpy(new_table, rthc_table_static, sizeof(rthc_table_static));
    rthc_table = new_table;
    rthc_limit *= 2;
  }

  rthc_table[rthc_count].key = *key;
  rthc_table[rthc_count].begin = begin;
  rthc_table[rthc_count].end = end;
  ++rthc_count;
  mdbx_rthc_unlock();
  return MDBX_SUCCESS;

bailout:
  mdbx_thread_key_delete(*key);
  mdbx_rthc_unlock();
  return rc;
}

__cold void mdbx_rthc_remove(mdbx_thread_key_t key) {
  mdbx_rthc_lock();
  mdbx_thread_key_delete(key);

  for (unsigned i = 0; i < rthc_count; ++i) {
    if (key == rthc_table[i].key) {
      const mdbx_pid_t self_pid = mdbx_getpid();
      for (MDBX_reader *rthc = rthc_table[i].begin; rthc < rthc_table[i].end;
           ++rthc)
        if (rthc->mr_pid == self_pid)
          rthc->mr_pid = 0;
      mdbx_coherent_barrier();
      if (--rthc_count > 0)
        rthc_table[i] = rthc_table[rthc_count];
      else if (rthc_table != rthc_table_static) {
        free(rthc_table);
        rthc_table = rthc_table_static;
        rthc_limit = RTHC_INITIAL_LIMIT;
      }
      break;
    }
  }

  mdbx_rthc_unlock();
}

/*----------------------------------------------------------------------------*/

/* Allocate an PNL.
 * Allocates memory for an PNL of the given size.
 * Returns PNL on success, NULL on failure. */
static MDBX_PNL mdbx_pnl_alloc(size_t size) {
  MDBX_PNL pl = malloc((size + 2) * sizeof(pgno_t));
  if (likely(pl)) {
    *pl++ = (pgno_t)size;
    *pl = 0;
  }
  return pl;
}

static MDBX_TXL mdbx_txl_alloc(void) {
  const size_t malloc_overhead = sizeof(void *) * 2;
  const size_t bytes = mdbx_roundup2(malloc_overhead + sizeof(txnid_t) * 61,
                                     MDBX_CACHELINE_SIZE) -
                       malloc_overhead;
  MDBX_TXL ptr = malloc(bytes);
  if (likely(ptr)) {
    *ptr++ = bytes / sizeof(txnid_t) - 2;
    *ptr = 0;
  }
  return ptr;
}

/* Free an PNL.
 * [in] pl The PNL to free. */
static void mdbx_pnl_free(MDBX_PNL pl) {
  if (likely(pl))
    free(pl - 1);
}

static void mdbx_txl_free(MDBX_TXL list) {
  if (likely(list))
    free(list - 1);
}

/* Append ID to PNL. The PNL must be big enough. */
static __inline void mdbx_pnl_xappend(MDBX_PNL pl, pgno_t id) {
  assert(pl[0] + (size_t)1 < MDBX_PNL_ALLOCLEN(pl));
  pl[pl[0] += 1] = id;
}

static bool mdbx_pnl_check(MDBX_PNL pl) {
  if (pl) {
    for (const pgno_t *ptr = pl + pl[0]; --ptr > pl;) {
      assert(ptr[0] > ptr[1]);
      if (unlikely(ptr[0] <= ptr[1]))
        return false;
    }
  }
  return true;
}

/* Sort an PNL.
 * [in,out] pnl The PNL to sort. */
static void __hot mdbx_pnl_sort(MDBX_PNL pnl) {
  /* Max possible depth of int-indexed tree * 2 items/level */
  int istack[sizeof(int) * CHAR_BIT * 2];
  int i, j, k, l, ir, jstack;
  pgno_t a;

/* Quicksort + Insertion sort for small arrays */
#define PNL_SMALL 8
#define PNL_SWAP(a, b)                                                         \
  do {                                                                         \
    pgno_t tmp_pgno = (a);                                                     \
    (a) = (b);                                                                 \
    (b) = tmp_pgno;                                                            \
  } while (0)

  ir = (int)pnl[0];
  l = 1;
  jstack = 0;
  while (1) {
    if (ir - l < PNL_SMALL) { /* Insertion sort */
      for (j = l + 1; j <= ir; j++) {
        a = pnl[j];
        for (i = j - 1; i >= 1; i--) {
          if (pnl[i] >= a)
            break;
          pnl[i + 1] = pnl[i];
        }
        pnl[i + 1] = a;
      }
      if (jstack == 0)
        break;
      ir = istack[jstack--];
      l = istack[jstack--];
    } else {
      k = (l + ir) >> 1; /* Choose median of left, center, right */
      PNL_SWAP(pnl[k], pnl[l + 1]);
      if (pnl[l] < pnl[ir])
        PNL_SWAP(pnl[l], pnl[ir]);

      if (pnl[l + 1] < pnl[ir])
        PNL_SWAP(pnl[l + 1], pnl[ir]);

      if (pnl[l] < pnl[l + 1])
        PNL_SWAP(pnl[l], pnl[l + 1]);

      i = l + 1;
      j = ir;
      a = pnl[l + 1];
      while (1) {
        do
          i++;
        while (pnl[i] > a);
        do
          j--;
        while (pnl[j] < a);
        if (j < i)
          break;
        PNL_SWAP(pnl[i], pnl[j]);
      }
      pnl[l + 1] = pnl[j];
      pnl[j] = a;
      jstack += 2;
      if (ir - i + 1 >= j - l) {
        istack[jstack] = ir;
        istack[jstack - 1] = i;
        ir = j - 1;
      } else {
        istack[jstack] = j - 1;
        istack[jstack - 1] = l;
        l = i;
      }
    }
  }
#undef PNL_SMALL
#undef PNL_SWAP
  assert(mdbx_pnl_check(pnl));
}

/* Search for an ID in an PNL.
 * [in] pl The PNL to search.
 * [in] id The ID to search for.
 * Returns The index of the first ID greater than or equal to id. */
static unsigned __hot mdbx_pnl_search(MDBX_PNL pnl, pgno_t id) {
  assert(mdbx_pnl_check(pnl));

  /* binary search of id in pl
   * if found, returns position of id
   * if not found, returns first position greater than id */
  unsigned base = 0;
  unsigned cursor = 1;
  int val = 0;
  unsigned n = pnl[0];

  while (n > 0) {
    unsigned pivot = n >> 1;
    cursor = base + pivot + 1;
    val = mdbx_cmp2int(pnl[cursor], id);

    if (val < 0) {
      n = pivot;
    } else if (val > 0) {
      base = cursor;
      n -= pivot + 1;
    } else {
      return cursor;
    }
  }

  if (val > 0)
    ++cursor;

  return cursor;
}

/* Shrink an PNL.
 * Return the PNL to the default size if it has grown larger.
 * [in,out] ppl Address of the PNL to shrink. */
static void mdbx_pnl_shrink(MDBX_PNL *ppl) {
  MDBX_PNL pl = *ppl - 1;
  if (unlikely(*pl > MDBX_PNL_UM_MAX)) {
    /* shrink to MDBX_PNL_UM_MAX */
    pl = realloc(pl, (MDBX_PNL_UM_MAX + 2) * sizeof(pgno_t));
    if (likely(pl)) {
      *pl++ = MDBX_PNL_UM_MAX;
      *ppl = pl;
    }
  }
}

/* Grow an PNL.
 * Return the PNL to the size growed by given number.
 * [in,out] ppl Address of the PNL to grow. */
static int mdbx_pnl_grow(MDBX_PNL *ppl, size_t num) {
  MDBX_PNL idn = *ppl - 1;
  /* grow it */
  idn = realloc(idn, (*idn + num + 2) * sizeof(pgno_t));
  if (unlikely(!idn))
    return MDBX_ENOMEM;
  *idn++ += (pgno_t)num;
  *ppl = idn;
  return 0;
}

static int mdbx_txl_grow(MDBX_TXL *ptr, size_t num) {
  MDBX_TXL list = *ptr - 1;
  /* grow it */
  list = realloc(list, ((size_t)*list + num + 2) * sizeof(txnid_t));
  if (unlikely(!list))
    return MDBX_ENOMEM;
  *list++ += num;
  *ptr = list;
  return 0;
}

/* Make room for num additional elements in an PNL.
 * [in,out] ppl Address of the PNL.
 * [in] num Number of elements to make room for.
 * Returns 0 on success, MDBX_ENOMEM on failure. */
static int mdbx_pnl_need(MDBX_PNL *ppl, size_t num) {
  MDBX_PNL pl = *ppl;
  num += pl[0];
  if (unlikely(num > pl[-1])) {
    num = (num + num / 4 + (256 + 2)) & -256;
    pl = realloc(pl - 1, num * sizeof(pgno_t));
    if (unlikely(!pl))
      return MDBX_ENOMEM;
    *pl++ = (pgno_t)num - 2;
    *ppl = pl;
  }
  return 0;
}

/* Append an ID onto an PNL.
 * [in,out] ppl Address of the PNL to append to.
 * [in] id The ID to append.
 * Returns 0 on success, MDBX_ENOMEM if the PNL is too large. */
static int mdbx_pnl_append(MDBX_PNL *ppl, pgno_t id) {
  MDBX_PNL pl = *ppl;
  /* Too big? */
  if (unlikely(pl[0] >= pl[-1])) {
    if (mdbx_pnl_grow(ppl, MDBX_PNL_UM_MAX))
      return MDBX_ENOMEM;
    pl = *ppl;
  }
  pl[0]++;
  pl[pl[0]] = id;
  return 0;
}

static int mdbx_txl_append(MDBX_TXL *ptr, txnid_t id) {
  MDBX_TXL list = *ptr;
  /* Too big? */
  if (unlikely(list[0] >= list[-1])) {
    if (mdbx_txl_grow(ptr, (size_t)list[0]))
      return MDBX_ENOMEM;
    list = *ptr;
  }
  list[0]++;
  list[list[0]] = id;
  return 0;
}

/* Append an PNL onto an PNL.
 * [in,out] ppl Address of the PNL to append to.
 * [in] app The PNL to append.
 * Returns 0 on success, MDBX_ENOMEM if the PNL is too large. */
static int mdbx_pnl_append_list(MDBX_PNL *ppl, MDBX_PNL app) {
  MDBX_PNL pnl = *ppl;
  /* Too big? */
  if (unlikely(pnl[0] + app[0] >= pnl[-1])) {
    if (mdbx_pnl_grow(ppl, app[0]))
      return MDBX_ENOMEM;
    pnl = *ppl;
  }
  memcpy(&pnl[pnl[0] + 1], &app[1], app[0] * sizeof(pgno_t));
  pnl[0] += app[0];
  return 0;
}

static int mdbx_txl_append_list(MDBX_TXL *ptr, MDBX_TXL append) {
  MDBX_TXL list = *ptr;
  /* Too big? */
  if (unlikely(list[0] + append[0] >= list[-1])) {
    if (mdbx_txl_grow(ptr, (size_t)append[0]))
      return MDBX_ENOMEM;
    list = *ptr;
  }
  memcpy(&list[list[0] + 1], &append[1], (size_t)append[0] * sizeof(txnid_t));
  list[0] += append[0];
  return 0;
}

/* Append an ID range onto an PNL.
 * [in,out] ppl Address of the PNL to append to.
 * [in] id The lowest ID to append.
 * [in] n Number of IDs to append.
 * Returns 0 on success, MDBX_ENOMEM if the PNL is too large. */
static int mdbx_pnl_append_range(MDBX_PNL *ppl, pgno_t id, size_t n) {
  pgno_t *pnl = *ppl, len = pnl[0];
  /* Too big? */
  if (unlikely(len + n > pnl[-1])) {
    if (mdbx_pnl_grow(ppl, n | MDBX_PNL_UM_MAX))
      return MDBX_ENOMEM;
    pnl = *ppl;
  }
  pnl[0] = len + (pgno_t)n;
  pnl += len;
  while (n)
    pnl[n--] = id++;
  return 0;
}

/* Merge an PNL onto an PNL. The destination PNL must be big enough.
 * [in] pl The PNL to merge into.
 * [in] merge The PNL to merge. */
static void __hot mdbx_pnl_xmerge(MDBX_PNL pnl, MDBX_PNL merge) {
  assert(mdbx_pnl_check(pnl));
  assert(mdbx_pnl_check(merge));
  pgno_t old_id, merge_id, i = merge[0], j = pnl[0], k = i + j, total = k;
  pnl[0] = ~(pgno_t)0; /* delimiter for pl scan below */
  old_id = pnl[j];
  while (i) {
    merge_id = merge[i--];
    for (; old_id < merge_id; old_id = pnl[--j])
      pnl[k--] = old_id;
    pnl[k--] = merge_id;
  }
  pnl[0] = total;
  assert(mdbx_pnl_check(pnl));
}

/* Search for an ID in an ID2L.
 * [in] pnl The ID2L to search.
 * [in] id The ID to search for.
 * Returns The index of the first ID2 whose mid member is greater than
 * or equal to id. */
static unsigned __hot mdbx_mid2l_search(MDBX_ID2L pnl, pgno_t id) {
  /* binary search of id in pnl
   * if found, returns position of id
   * if not found, returns first position greater than id */
  unsigned base = 0;
  unsigned cursor = 1;
  int val = 0;
  unsigned n = (unsigned)pnl[0].mid;

  while (n > 0) {
    unsigned pivot = n >> 1;
    cursor = base + pivot + 1;
    val = mdbx_cmp2int(id, pnl[cursor].mid);

    if (val < 0) {
      n = pivot;
    } else if (val > 0) {
      base = cursor;
      n -= pivot + 1;
    } else {
      return cursor;
    }
  }

  if (val > 0)
    ++cursor;

  return cursor;
}

/* Insert an ID2 into a ID2L.
 * [in,out] pnl The ID2L to insert into.
 * [in] id The ID2 to insert.
 * Returns 0 on success, -1 if the ID was already present in the ID2L. */
static int mdbx_mid2l_insert(MDBX_ID2L pnl, MDBX_ID2 *id) {
  unsigned x = mdbx_mid2l_search(pnl, id->mid);
  if (unlikely(x < 1))
    return /* internal error */ -2;

  if (x <= pnl[0].mid && pnl[x].mid == id->mid)
    return /* duplicate */ -1;

  if (unlikely(pnl[0].mid >= MDBX_PNL_UM_MAX))
    return /* too big */ -2;

  /* insert id */
  pnl[0].mid++;
  for (unsigned i = (unsigned)pnl[0].mid; i > x; i--)
    pnl[i] = pnl[i - 1];
  pnl[x] = *id;
  return 0;
}

/* Append an ID2 into a ID2L.
 * [in,out] pnl The ID2L to append into.
 * [in] id The ID2 to append.
 * Returns 0 on success, -2 if the ID2L is too big. */
static int mdbx_mid2l_append(MDBX_ID2L pnl, MDBX_ID2 *id) {
  /* Too big? */
  if (unlikely(pnl[0].mid >= MDBX_PNL_UM_MAX))
    return -2;

  pnl[0].mid++;
  pnl[pnl[0].mid] = *id;
  return 0;
}

/*----------------------------------------------------------------------------*/

int mdbx_runtime_flags = MDBX_DBG_PRINT
#if MDBX_DEBUG
                         | MDBX_DBG_ASSERT
#endif
#if MDBX_DEBUG > 1
                         | MDBX_DBG_TRACE
#endif
#if MDBX_DEBUG > 2
                         | MDBX_DBG_AUDIT
#endif
#if MDBX_DEBUG > 3
                         | MDBX_DBG_EXTRA
#endif
    ;

MDBX_debug_func *mdbx_debug_logger;

static int mdbx_page_alloc(MDBX_cursor *mc, unsigned num, MDBX_page **mp,
                           int flags);
static int mdbx_page_new(MDBX_cursor *mc, uint32_t flags, unsigned num,
                         MDBX_page **mp);
static int mdbx_page_touch(MDBX_cursor *mc);
static int mdbx_cursor_touch(MDBX_cursor *mc);

#define MDBX_END_NAMES                                                         \
  {                                                                            \
    "committed", "empty-commit", "abort", "reset", "reset-tmp", "fail-begin",  \
        "fail-beginchild"                                                      \
  }
enum {
  /* mdbx_txn_end operation number, for logging */
  MDBX_END_COMMITTED,
  MDBX_END_EMPTY_COMMIT,
  MDBX_END_ABORT,
  MDBX_END_RESET,
  MDBX_END_RESET_TMP,
  MDBX_END_FAIL_BEGIN,
  MDBX_END_FAIL_BEGINCHILD
};
#define MDBX_END_OPMASK 0x0F  /* mask for mdbx_txn_end() operation number */
#define MDBX_END_UPDATE 0x10  /* update env state (DBIs) */
#define MDBX_END_FREE 0x20    /* free txn unless it is MDBX_env.me_txn0 */
#define MDBX_END_EOTDONE 0x40 /* txn's cursors already closed */
#define MDBX_END_SLOT 0x80    /* release any reader slot if MDBX_NOTLS */
static int mdbx_txn_end(MDBX_txn *txn, unsigned mode);

static int mdbx_page_get(MDBX_cursor *mc, pgno_t pgno, MDBX_page **mp,
                         int *lvl);
static int mdbx_page_search_root(MDBX_cursor *mc, MDBX_val *key, int modify);

#define MDBX_PS_MODIFY 1
#define MDBX_PS_ROOTONLY 2
#define MDBX_PS_FIRST 4
#define MDBX_PS_LAST 8
static int mdbx_page_search(MDBX_cursor *mc, MDBX_val *key, int flags);
static int mdbx_page_merge(MDBX_cursor *csrc, MDBX_cursor *cdst);

#define MDBX_SPLIT_REPLACE MDBX_APPENDDUP /* newkey is not new */
static int mdbx_page_split(MDBX_cursor *mc, MDBX_val *newkey, MDBX_val *newdata,
                           pgno_t newpgno, unsigned nflags);

static int mdbx_read_header(MDBX_env *env, MDBX_meta *meta);
static int mdbx_sync_locked(MDBX_env *env, unsigned flags,
                            MDBX_meta *const pending);
static void mdbx_env_close0(MDBX_env *env);

static MDBX_node *mdbx_node_search(MDBX_cursor *mc, MDBX_val *key, int *exactp);
static int mdbx_node_add(MDBX_cursor *mc, unsigned indx, MDBX_val *key,
                         MDBX_val *data, pgno_t pgno, unsigned flags);
static void mdbx_node_del(MDBX_cursor *mc, size_t ksize);
static void mdbx_node_shrink(MDBX_page *mp, unsigned indx);
static int mdbx_node_move(MDBX_cursor *csrc, MDBX_cursor *cdst, int fromleft);
static int mdbx_node_read(MDBX_cursor *mc, MDBX_node *leaf, MDBX_val *data);
static size_t mdbx_leaf_size(MDBX_env *env, MDBX_val *key, MDBX_val *data);
static size_t mdbx_branch_size(MDBX_env *env, MDBX_val *key);

static int mdbx_rebalance(MDBX_cursor *mc);
static int mdbx_update_key(MDBX_cursor *mc, MDBX_val *key);

static void mdbx_cursor_pop(MDBX_cursor *mc);
static int mdbx_cursor_push(MDBX_cursor *mc, MDBX_page *mp);

static int mdbx_cursor_del0(MDBX_cursor *mc);
static int mdbx_del0(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
                     unsigned flags);
static int mdbx_cursor_sibling(MDBX_cursor *mc, int move_right);
static int mdbx_cursor_next(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                            MDBX_cursor_op op);
static int mdbx_cursor_prev(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                            MDBX_cursor_op op);
static int mdbx_cursor_set(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                           MDBX_cursor_op op, int *exactp);
static int mdbx_cursor_first(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data);
static int mdbx_cursor_last(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data);

static void mdbx_cursor_init(MDBX_cursor *mc, MDBX_txn *txn, MDBX_dbi dbi,
                             MDBX_xcursor *mx);
static void mdbx_xcursor_init0(MDBX_cursor *mc);
static void mdbx_xcursor_init1(MDBX_cursor *mc, MDBX_node *node);
static void mdbx_xcursor_init2(MDBX_cursor *mc, MDBX_xcursor *src_mx,
                               int force);

static int mdbx_drop0(MDBX_cursor *mc, int subs);

static MDBX_cmp_func mdbx_cmp_memn, mdbx_cmp_memnr, mdbx_cmp_int_ai,
    mdbx_cmp_int_a2, mdbx_cmp_int_ua;

static const char *__mdbx_strerr(int errnum) {
  /* Table of descriptions for MDBX errors */
  static const char *const tbl[] = {
      "MDBX_KEYEXIST: Key/data pair already exists",
      "MDBX_NOTFOUND: No matching key/data pair found",
      "MDBX_PAGE_NOTFOUND: Requested page not found",
      "MDBX_CORRUPTED: Database is corrupted",
      "MDBX_PANIC: Update of meta page failed or environment had fatal error",
      "MDBX_VERSION_MISMATCH: DB version mismatch libmdbx",
      "MDBX_INVALID: File is not an MDBX file",
      "MDBX_MAP_FULL: Environment mapsize limit reached",
      "MDBX_DBS_FULL: Too may DBI (maxdbs reached)",
      "MDBX_READERS_FULL: Too many readers (maxreaders reached)",
      NULL /* MDBX_TLS_FULL (-30789): unused in MDBX */,
      "MDBX_TXN_FULL: Transaction has too many dirty pages - transaction too "
      "big",
      "MDBX_CURSOR_FULL: Internal error - cursor stack limit reached",
      "MDBX_PAGE_FULL: Internal error - page has no more space",
      "MDBX_MAP_RESIZED: Database contents grew beyond environment mapsize",
      "MDBX_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed",
      "MDBX_BAD_RSLOT: Invalid reuse of reader locktable slot",
      "MDBX_BAD_TXN: Transaction must abort, has a child, or is invalid",
      "MDBX_BAD_VALSIZE: Unsupported size of key/DB name/data, or wrong "
      "DUPFIXED size",
      "MDBX_BAD_DBI: The specified DBI handle was closed/changed unexpectedly",
      "MDBX_PROBLEM: Unexpected problem - txn should abort",
  };

  if (errnum >= MDBX_KEYEXIST && errnum <= MDBX_LAST_ERRCODE) {
    int i = errnum - MDBX_KEYEXIST;
    return tbl[i];
  }

  switch (errnum) {
  case MDBX_SUCCESS:
    return "MDBX_SUCCESS: Successful";
  case MDBX_EMULTIVAL:
    return "MDBX_EMULTIVAL: Unable to update multi-value for the given key";
  case MDBX_EBADSIGN:
    return "MDBX_EBADSIGN: Wrong signature of a runtime object(s)";
  case MDBX_WANNA_RECOVERY:
    return "MDBX_WANNA_RECOVERY: Database should be recovered, but this could "
           "NOT be done in a read-only mode";
  case MDBX_EKEYMISMATCH:
    return "MDBX_EKEYMISMATCH: The given key value is mismatched to the "
           "current cursor position";
  case MDBX_TOO_LARGE:
    return "MDBX_TOO_LARGE: Database is too large for current system, "
           "e.g. could NOT be mapped into RAM";
  case MDBX_THREAD_MISMATCH:
    return "MDBX_THREAD_MISMATCH: A thread has attempted to use a not "
           "owned object, e.g. a transaction that started by another thread";
  default:
    return NULL;
  }
}

const char *__cold mdbx_strerror_r(int errnum, char *buf, size_t buflen) {
  const char *msg = __mdbx_strerr(errnum);
  if (!msg) {
    if (!buflen || buflen > INT_MAX)
      return NULL;
#ifdef _MSC_VER
    size_t size = FormatMessageA(
        FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL,
        errnum, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), buf, (DWORD)buflen,
        NULL);
    return size ? buf : NULL;
#elif defined(_GNU_SOURCE)
    /* GNU-specific */
    msg = strerror_r(errnum, buf, buflen);
#elif (_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
    /* XSI-compliant */
    int rc = strerror_r(errnum, buf, buflen);
    if (rc) {
      rc = snprintf(buf, buflen, "error %d", errnum);
      assert(rc > 0);
    }
    return buf;
#else
    strncpy(buf, strerror(errnum), buflen);
    buf[buflen - 1] = '\0';
    return buf;
#endif
  }
  return msg;
}

const char *__cold mdbx_strerror(int errnum) {
  const char *msg = __mdbx_strerr(errnum);
  if (!msg) {
#ifdef _MSC_VER
    static __thread char buffer[1024];
    size_t size = FormatMessageA(
        FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL,
        errnum, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), buffer,
        sizeof(buffer), NULL);
    if (size)
      msg = buffer;
#else
    msg = strerror(errnum);
#endif
  }
  return msg;
}

static txnid_t mdbx_oomkick(MDBX_env *env, const txnid_t laggard);

void __cold mdbx_debug_log(int type, const char *function, int line,
                           const char *fmt, ...) {
  va_list args;

  va_start(args, fmt);
  if (mdbx_debug_logger)
    mdbx_debug_logger(type, function, line, fmt, args);
  else {
    if (function && line > 0)
      fprintf(stderr, "%s:%d ", function, line);
    else if (function)
      fprintf(stderr, "%s: ", function);
    else if (line > 0)
      fprintf(stderr, "%d: ", line);
    vfprintf(stderr, fmt, args);
  }
  va_end(args);
}

/* Dump a key in ascii or hexadecimal. */
char *mdbx_dkey(const MDBX_val *key, char *const buf, const size_t bufsize) {
  if (!key)
    return "<null>";
  if (!buf || bufsize < 4)
    return nullptr;
  if (!key->iov_len)
    return "<empty>";

  const uint8_t *const data = key->iov_base;
  bool is_ascii = true;
  unsigned i;
  for (i = 0; is_ascii && i < key->iov_len; i++)
    if (data[i] < ' ' || data[i] > 127)
      is_ascii = false;

  if (is_ascii) {
    int len =
        snprintf(buf, bufsize, "%.*s",
                 (key->iov_len > INT_MAX) ? INT_MAX : (int)key->iov_len, data);
    assert(len > 0 && (unsigned)len < bufsize);
    (void)len;
  } else {
    char *const detent = buf + bufsize - 2;
    char *ptr = buf;
    *ptr++ = '<';
    for (i = 0; i < key->iov_len; i++) {
      const ptrdiff_t left = detent - ptr;
      assert(left > 0);
      int len = snprintf(ptr, left, "%02x", data[i]);
      if (len < 0 || len >= left)
        break;
      ptr += len;
    }
    if (ptr < detent) {
      ptr[0] = '>';
      ptr[1] = '\0';
    }
  }
  return buf;
}

#if 0  /* LY: debug stuff */
static const char *mdbx_leafnode_type(MDBX_node *n) {
  static char *const tp[2][2] = {{"", ": DB"}, {": sub-page", ": sub-DB"}};
  return F_ISSET(n->mn_flags, F_BIGDATA) ? ": overflow page"
                                         : tp[F_ISSET(n->mn_flags, F_DUPDATA)]
                                             [F_ISSET(n->mn_flags, F_SUBDATA)];
}

/* Display all the keys in the page. */
static void mdbx_page_list(MDBX_page *mp) {
  pgno_t pgno = mp->mp_pgno;
  const char *type, *state = (mp->mp_flags & P_DIRTY) ? ", dirty" : "";
  MDBX_node *node;
  unsigned i, nkeys, nsize, total = 0;
  MDBX_val key;
  DKBUF;

  switch (mp->mp_flags &
          (P_BRANCH | P_LEAF | P_LEAF2 | P_META | P_OVERFLOW | P_SUBP)) {
  case P_BRANCH:
    type = "Branch page";
    break;
  case P_LEAF:
    type = "Leaf page";
    break;
  case P_LEAF | P_SUBP:
    type = "Sub-page";
    break;
  case P_LEAF | P_LEAF2:
    type = "LEAF2 page";
    break;
  case P_LEAF | P_LEAF2 | P_SUBP:
    type = "LEAF2 sub-page";
    break;
  case P_OVERFLOW:
    mdbx_print("Overflow page %" PRIu64 " pages %u%s\n", pgno, mp->mp_pages,
               state);
    return;
  case P_META:
    mdbx_print("Meta-page %" PRIu64 " txnid %" PRIu64 "\n", pgno,
               ((MDBX_meta *)PAGEDATA(mp))->mm_txnid);
    return;
  default:
    mdbx_print("Bad page %" PRIu64 " flags 0x%X\n", pgno, mp->mp_flags);
    return;
  }

  nkeys = NUMKEYS(mp);
  mdbx_print("%s %" PRIu64 " numkeys %u%s\n", type, pgno, nkeys, state);

  for (i = 0; i < nkeys; i++) {
    if (IS_LEAF2(mp)) { /* LEAF2 pages have no mp_ptrs[] or node headers */
      key.iov_len = nsize = mp->mp_leaf2_ksize;
      key.iov_base = LEAF2KEY(mp, i, nsize);
      total += nsize;
      mdbx_print("key %u: nsize %u, %s\n", i, nsize, DKEY(&key));
      continue;
    }
    node = NODEPTR(mp, i);
    key.iov_len = node->mn_ksize;
    key.iov_base = node->mn_data;
    nsize = NODESIZE + key.iov_len;
    if (IS_BRANCH(mp)) {
      mdbx_print("key %u: page %" PRIu64 ", %s\n", i, NODEPGNO(node),
                 DKEY(&key));
      total += nsize;
    } else {
      if (F_ISSET(node->mn_flags, F_BIGDATA))
        nsize += sizeof(pgno_t);
      else
        nsize += NODEDSZ(node);
      total += nsize;
      nsize += sizeof(indx_t);
      mdbx_print("key %u: nsize %u, %s%s\n", i, nsize, DKEY(&key),
                 mdbx_leafnode_type(node));
    }
    total = EVEN(total);
  }
  mdbx_print("Total: header %u + contents %u + unused %u\n",
             IS_LEAF2(mp) ? PAGEHDRSZ : PAGEHDRSZ + mp->mp_lower, total,
             SIZELEFT(mp));
}

static void mdbx_cursor_chk(MDBX_cursor *mc) {
  unsigned i;
  MDBX_node *node;
  MDBX_page *mp;

  if (!mc->mc_snum || !(mc->mc_flags & C_INITIALIZED))
    return;
  for (i = 0; i < mc->mc_top; i++) {
    mp = mc->mc_pg[i];
    node = NODEPTR(mp, mc->mc_ki[i]);
    if (unlikely(NODEPGNO(node) != mc->mc_pg[i + 1]->mp_pgno))
      mdbx_print("oops!\n");
  }
  if (unlikely(mc->mc_ki[i] >= NUMKEYS(mc->mc_pg[i])))
    mdbx_print("ack!\n");
  if (XCURSOR_INITED(mc)) {
    node = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
    if (((node->mn_flags & (F_DUPDATA | F_SUBDATA)) == F_DUPDATA) &&
        mc->mc_xcursor->mx_cursor.mc_pg[0] != NODEDATA(node)) {
      mdbx_print("blah!\n");
    }
  }
}
#endif /* 0 */

/* Count all the pages in each DB and in the freelist and make sure
 * it matches the actual number of pages being used.
 * All named DBs must be open for a correct count. */
static void mdbx_audit(MDBX_txn *txn) {
  MDBX_cursor mc;
  MDBX_val key, data;
  int rc;

  pgno_t freecount = 0;
  mdbx_cursor_init(&mc, txn, FREE_DBI, NULL);
  while ((rc = mdbx_cursor_get(&mc, &key, &data, MDBX_NEXT)) == 0)
    freecount += *(pgno_t *)data.iov_base;
  mdbx_tassert(txn, rc == MDBX_NOTFOUND);

  pgno_t count = 0;
  for (MDBX_dbi i = 0; i < txn->mt_numdbs; i++) {
    MDBX_xcursor mx;
    if (!(txn->mt_dbflags[i] & DB_VALID))
      continue;
    mdbx_cursor_init(&mc, txn, i, &mx);
    if (txn->mt_dbs[i].md_root == P_INVALID)
      continue;
    count += txn->mt_dbs[i].md_branch_pages + txn->mt_dbs[i].md_leaf_pages +
             txn->mt_dbs[i].md_overflow_pages;
    if (txn->mt_dbs[i].md_flags & MDBX_DUPSORT) {
      rc = mdbx_page_search(&mc, NULL, MDBX_PS_FIRST);
      for (; rc == MDBX_SUCCESS; rc = mdbx_cursor_sibling(&mc, 1)) {
        MDBX_page *mp = mc.mc_pg[mc.mc_top];
        for (unsigned j = 0; j < NUMKEYS(mp); j++) {
          MDBX_node *leaf = NODEPTR(mp, j);
          if (leaf->mn_flags & F_SUBDATA) {
            MDBX_db db;
            memcpy(&db, NODEDATA(leaf), sizeof(db));
            count +=
                db.md_branch_pages + db.md_leaf_pages + db.md_overflow_pages;
          }
        }
      }
      mdbx_tassert(txn, rc == MDBX_NOTFOUND);
    }
  }
  if (freecount + count + NUM_METAS != txn->mt_next_pgno) {
    mdbx_print("audit: %" PRIaTXN " freecount: %" PRIaPGNO " count: %" PRIaPGNO
               " total: %" PRIaPGNO " next_pgno: %" PRIaPGNO "\n",
               txn->mt_txnid, freecount, count + NUM_METAS,
               freecount + count + NUM_METAS, txn->mt_next_pgno);
  }
}

int mdbx_cmp(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
             const MDBX_val *b) {
  mdbx_assert(NULL, txn->mt_signature == MDBX_MT_SIGNATURE);
  return txn->mt_dbxs[dbi].md_cmp(a, b);
}

int mdbx_dcmp(MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
              const MDBX_val *b) {
  mdbx_assert(NULL, txn->mt_signature == MDBX_MT_SIGNATURE);
  return txn->mt_dbxs[dbi].md_dcmp(a, b);
}

/* Allocate memory for a page.
 * Re-use old malloc'd pages first for singletons, otherwise just malloc.
 * Set MDBX_TXN_ERROR on failure. */
static MDBX_page *mdbx_page_malloc(MDBX_txn *txn, unsigned num) {
  MDBX_env *env = txn->mt_env;
  MDBX_page *np = env->me_dpages;
  size_t size = env->me_psize;
  if (likely(num == 1 && np)) {
    ASAN_UNPOISON_MEMORY_REGION(np, size);
    VALGRIND_MEMPOOL_ALLOC(env, np, size);
    VALGRIND_MAKE_MEM_DEFINED(&np->mp_next, sizeof(np->mp_next));
    env->me_dpages = np->mp_next;
  } else {
    size = pgno2bytes(env, num);
    np = malloc(size);
    if (unlikely(!np)) {
      txn->mt_flags |= MDBX_TXN_ERROR;
      return np;
    }
    VALGRIND_MEMPOOL_ALLOC(env, np, size);
  }

  if ((env->me_flags & MDBX_NOMEMINIT) == 0) {
    /* For a single page alloc, we init everything after the page header.
     * For multi-page, we init the final page; if the caller needed that
     * many pages they will be filling in at least up to the last page. */
    size_t skip = PAGEHDRSZ;
    if (num > 1)
      skip += pgno2bytes(env, num - 1);
    memset((char *)np + skip, 0, size - skip);
  }
  VALGRIND_MAKE_MEM_UNDEFINED(np, size);
  np->mp_flags = 0;
  np->mp_pages = num;
  return np;
}

/* Free a single page.
 * Saves single pages to a list, for future reuse.
 * (This is not used for multi-page overflow pages.) */
static __inline void mdbx_page_free(MDBX_env *env, MDBX_page *mp) {
  mp->mp_next = env->me_dpages;
  VALGRIND_MEMPOOL_FREE(env, mp);
  env->me_dpages = mp;
}

/* Free a dirty page */
static void mdbx_dpage_free(MDBX_env *env, MDBX_page *dp) {
  if (!IS_OVERFLOW(dp) || dp->mp_pages == 1) {
    mdbx_page_free(env, dp);
  } else {
    /* large pages just get freed directly */
    VALGRIND_MEMPOOL_FREE(env, dp);
    free(dp);
  }
}

/* Return all dirty pages to dpage list */
static void mdbx_dlist_free(MDBX_txn *txn) {
  MDBX_env *env = txn->mt_env;
  MDBX_ID2L dl = txn->mt_rw_dirtylist;
  size_t i, n = dl[0].mid;

  for (i = 1; i <= n; i++) {
    mdbx_dpage_free(env, dl[i].mptr);
  }
  dl[0].mid = 0;
}

static size_t bytes_align2os_bytes(const MDBX_env *env, size_t bytes) {
  return mdbx_roundup2(mdbx_roundup2(bytes, env->me_psize), env->me_os_psize);
}

static void __cold mdbx_kill_page(MDBX_env *env, pgno_t pgno) {
  const size_t offs = pgno2bytes(env, pgno);
  const size_t shift = offsetof(MDBX_page, mp_pages);

  if (env->me_flags & MDBX_WRITEMAP) {
    MDBX_page *mp = (MDBX_page *)(env->me_map + offs);
    memset(&mp->mp_pages, 0x6F /* 'o', 111 */, env->me_psize - shift);
    VALGRIND_MAKE_MEM_NOACCESS(&mp->mp_pages, env->me_psize - shift);
    ASAN_POISON_MEMORY_REGION(&mp->mp_pages, env->me_psize - shift);
  } else {
    intptr_t len = env->me_psize - shift;
    void *buf = alloca(len);
    memset(buf, 0x6F /* 'o', 111 */, len);
    (void)mdbx_pwrite(env->me_fd, buf, len, offs + shift);
  }
}

/* Loosen or free a single page.
 *
 * Saves single pages to a list for future reuse
 * in this same txn. It has been pulled from the freeDB
 * and already resides on the dirty list, but has been
 * deleted. Use these pages first before pulling again
 * from the freeDB.
 *
 * If the page wasn't dirtied in this txn, just add it
 * to this txn's free list. */
static int mdbx_page_loose(MDBX_cursor *mc, MDBX_page *mp) {
  int loose = 0;
  const pgno_t pgno = mp->mp_pgno;
  MDBX_txn *txn = mc->mc_txn;

  if ((mp->mp_flags & P_DIRTY) && mc->mc_dbi != FREE_DBI) {
    if (txn->mt_parent) {
      MDBX_ID2 *dl = txn->mt_rw_dirtylist;
      /* If txn has a parent,
       * make sure the page is in our dirty list. */
      if (dl[0].mid) {
        unsigned x = mdbx_mid2l_search(dl, pgno);
        if (x <= dl[0].mid && dl[x].mid == pgno) {
          if (unlikely(mp != dl[x].mptr)) { /* bad cursor? */
            mdbx_error("wrong page 0x%p #%" PRIaPGNO
                       " in the dirtylist[%d], expecting %p",
                       dl[x].mptr, pgno, x, mp);
            mc->mc_flags &= ~(C_INITIALIZED | C_EOF);
            txn->mt_flags |= MDBX_TXN_ERROR;
            return MDBX_PROBLEM;
          }
          /* ok, it's ours */
          loose = 1;
        }
      }
    } else {
      /* no parent txn, so it's just ours */
      loose = 1;
    }
  }
  if (loose) {
    mdbx_debug("loosen db %d page %" PRIaPGNO, DDBI(mc), mp->mp_pgno);
    MDBX_page **link = &NEXT_LOOSE_PAGE(mp);
    if (unlikely(txn->mt_env->me_flags & MDBX_PAGEPERTURB)) {
      mdbx_kill_page(txn->mt_env, pgno);
      VALGRIND_MAKE_MEM_UNDEFINED(link, sizeof(MDBX_page *));
      ASAN_UNPOISON_MEMORY_REGION(link, sizeof(MDBX_page *));
    }
    *link = txn->mt_loose_pages;
    txn->mt_loose_pages = mp;
    txn->mt_loose_count++;
    mp->mp_flags |= P_LOOSE;
  } else {
    int rc = mdbx_pnl_append(&txn->mt_befree_pages, pgno);
    if (unlikely(rc))
      return rc;
  }

  return MDBX_SUCCESS;
}

/* Set or clear P_KEEP in dirty, non-overflow, non-sub pages watched by txn.
 *
 * [in] mc      A cursor handle for the current operation.
 * [in] pflags  Flags of the pages to update:
 *                - P_DIRTY to set P_KEEP,
 *                - P_DIRTY|P_KEEP to clear it.
 * [in] all     No shortcuts. Needed except after a full mdbx_page_flush().
 *
 * Returns 0 on success, non-zero on failure. */
static int mdbx_pages_xkeep(MDBX_cursor *mc, unsigned pflags, bool all) {
  const unsigned Mask = P_SUBP | P_DIRTY | P_LOOSE | P_KEEP;
  MDBX_txn *txn = mc->mc_txn;
  MDBX_cursor *m3, *m0 = mc;
  MDBX_xcursor *mx;
  MDBX_page *dp, *mp;
  MDBX_node *leaf;
  unsigned i, j;
  int rc = MDBX_SUCCESS, level;

  /* Mark pages seen by cursors: First m0, then tracked cursors */
  for (i = txn->mt_numdbs;;) {
    if (mc->mc_flags & C_INITIALIZED) {
      for (m3 = mc;; m3 = &mx->mx_cursor) {
        mp = NULL;
        for (j = 0; j < m3->mc_snum; j++) {
          mp = m3->mc_pg[j];
          if ((mp->mp_flags & Mask) == pflags)
            mp->mp_flags ^= P_KEEP;
        }
        mx = m3->mc_xcursor;
        /* Proceed to mx if it is at a sub-database */
        if (!(mx && (mx->mx_cursor.mc_flags & C_INITIALIZED)))
          break;
        if (!(mp && (mp->mp_flags & P_LEAF)))
          break;
        leaf = NODEPTR(mp, m3->mc_ki[j - 1]);
        if (!(leaf->mn_flags & F_SUBDATA))
          break;
      }
    }
    mc = mc->mc_next;
    for (; !mc || mc == m0; mc = txn->mt_cursors[--i])
      if (i == 0)
        goto mark_done;
  }

mark_done:
  if (all) {
    /* Mark dirty root pages */
    for (i = 0; i < txn->mt_numdbs; i++) {
      if (txn->mt_dbflags[i] & DB_DIRTY) {
        pgno_t pgno = txn->mt_dbs[i].md_root;
        if (pgno == P_INVALID)
          continue;
        if (unlikely((rc = mdbx_page_get(m0, pgno, &dp, &level)) !=
                     MDBX_SUCCESS))
          break;
        if ((dp->mp_flags & Mask) == pflags && level <= 1)
          dp->mp_flags ^= P_KEEP;
      }
    }
  }

  return rc;
}

static int mdbx_page_flush(MDBX_txn *txn, pgno_t keep);

/* Spill pages from the dirty list back to disk.
 * This is intended to prevent running into MDBX_TXN_FULL situations,
 * but note that they may still occur in a few cases:
 *
 * 1) our estimate of the txn size could be too small. Currently this
 *  seems unlikely, except with a large number of MDBX_MULTIPLE items.
 *
 * 2) child txns may run out of space if their parents dirtied a
 *  lot of pages and never spilled them. TODO: we probably should do
 *  a preemptive spill during mdbx_txn_begin() of a child txn, if
 *  the parent's dirtyroom is below a given threshold.
 *
 * Otherwise, if not using nested txns, it is expected that apps will
 * not run into MDBX_TXN_FULL any more. The pages are flushed to disk
 * the same way as for a txn commit, e.g. their P_DIRTY flag is cleared.
 * If the txn never references them again, they can be left alone.
 * If the txn only reads them, they can be used without any fuss.
 * If the txn writes them again, they can be dirtied immediately without
 * going thru all of the work of mdbx_page_touch(). Such references are
 * handled by mdbx_page_unspill().
 *
 * Also note, we never spill DB root pages, nor pages of active cursors,
 * because we'll need these back again soon anyway. And in nested txns,
 * we can't spill a page in a child txn if it was already spilled in a
 * parent txn. That would alter the parent txns' data even though
 * the child hasn't committed yet, and we'd have no way to undo it if
 * the child aborted.
 *
 * [in] m0    cursor A cursor handle identifying the transaction and
 *            database for which we are checking space.
 * [in] key   For a put operation, the key being stored.
 * [in] data  For a put operation, the data being stored.
 *
 * Returns 0 on success, non-zero on failure. */
static int mdbx_page_spill(MDBX_cursor *m0, MDBX_val *key, MDBX_val *data) {
  MDBX_txn *txn = m0->mc_txn;
  MDBX_ID2L dl = txn->mt_rw_dirtylist;

  if (m0->mc_flags & C_SUB)
    return MDBX_SUCCESS;

  /* Estimate how much space this op will take */
  pgno_t i = m0->mc_db->md_depth;
  /* Named DBs also dirty the main DB */
  if (m0->mc_dbi >= CORE_DBS)
    i += txn->mt_dbs[MAIN_DBI].md_depth;
  /* For puts, roughly factor in the key+data size */
  if (key)
    i += bytes2pgno(txn->mt_env, LEAFSIZE(key, data) + txn->mt_env->me_psize);
  i += i; /* double it for good measure */
  pgno_t need = i;

  if (txn->mt_dirtyroom > i)
    return MDBX_SUCCESS;

  if (!txn->mt_spill_pages) {
    txn->mt_spill_pages = mdbx_pnl_alloc(MDBX_PNL_UM_MAX);
    if (unlikely(!txn->mt_spill_pages))
      return MDBX_ENOMEM;
  } else {
    /* purge deleted slots */
    MDBX_PNL sl = txn->mt_spill_pages;
    pgno_t num = sl[0], j = 0;
    for (i = 1; i <= num; i++) {
      if (!(sl[i] & 1))
        sl[++j] = sl[i];
    }
    sl[0] = j;
  }

  /* Preserve pages which may soon be dirtied again */
  int rc = mdbx_pages_xkeep(m0, P_DIRTY, true);
  if (unlikely(rc != MDBX_SUCCESS))
    goto bailout;

  /* Less aggressive spill - we originally spilled the entire dirty list,
   * with a few exceptions for cursor pages and DB root pages. But this
   * turns out to be a lot of wasted effort because in a large txn many
   * of those pages will need to be used again. So now we spill only 1/8th
   * of the dirty pages. Testing revealed this to be a good tradeoff,
   * better than 1/2, 1/4, or 1/10. */
  if (need < MDBX_PNL_UM_MAX / 8)
    need = MDBX_PNL_UM_MAX / 8;

  /* Save the page IDs of all the pages we're flushing */
  /* flush from the tail forward, this saves a lot of shifting later on. */
  for (i = dl[0].mid; i && need; i--) {
    pgno_t pn = dl[i].mid << 1;
    MDBX_page *dp = dl[i].mptr;
    if (dp->mp_flags & (P_LOOSE | P_KEEP))
      continue;
    /* Can't spill twice,
     * make sure it's not already in a parent's spill list. */
    if (txn->mt_parent) {
      MDBX_txn *tx2;
      for (tx2 = txn->mt_parent; tx2; tx2 = tx2->mt_parent) {
        if (tx2->mt_spill_pages) {
          unsigned j = mdbx_pnl_search(tx2->mt_spill_pages, pn);
          if (j <= tx2->mt_spill_pages[0] && tx2->mt_spill_pages[j] == pn) {
            dp->mp_flags |= P_KEEP;
            break;
          }
        }
      }
      if (tx2)
        continue;
    }
    rc = mdbx_pnl_append(&txn->mt_spill_pages, pn);
    if (unlikely(rc != MDBX_SUCCESS))
      goto bailout;
    need--;
  }
  mdbx_pnl_sort(txn->mt_spill_pages);

  /* Flush the spilled part of dirty list */
  rc = mdbx_page_flush(txn, i);
  if (unlikely(rc != MDBX_SUCCESS))
    goto bailout;

  /* Reset any dirty pages we kept that page_flush didn't see */
  rc = mdbx_pages_xkeep(m0, P_DIRTY | P_KEEP, i != 0);

bailout:
  txn->mt_flags |= rc ? MDBX_TXN_ERROR : MDBX_TXN_SPILLS;
  return rc;
}

/*----------------------------------------------------------------------------*/

#define METAPAGE(env, n) (&pgno2page(env, n)->mp_meta)

#define METAPAGE_END(env) METAPAGE(env, NUM_METAS)

static __inline txnid_t meta_txnid(const MDBX_env *env, const MDBX_meta *meta,
                                   bool allow_volatile) {
  mdbx_assert(env, meta >= METAPAGE(env, 0) || meta < METAPAGE_END(env));
  txnid_t a = meta->mm_txnid_a;
  txnid_t b = meta->mm_txnid_b;
  if (allow_volatile)
    return (a == b) ? a : 0;
  mdbx_assert(env, a == b);
  return a;
}

static __inline txnid_t mdbx_meta_txnid_stable(const MDBX_env *env,
                                               const MDBX_meta *meta) {
  return meta_txnid(env, meta, false);
}

static __inline txnid_t mdbx_meta_txnid_fluid(const MDBX_env *env,
                                              const MDBX_meta *meta) {
  return meta_txnid(env, meta, true);
}

static __inline void mdbx_meta_update_begin(const MDBX_env *env,
                                            MDBX_meta *meta, txnid_t txnid) {
  mdbx_assert(env, meta >= METAPAGE(env, 0) || meta < METAPAGE_END(env));
  mdbx_assert(env, meta->mm_txnid_a < txnid && meta->mm_txnid_b < txnid);
  meta->mm_txnid_a = txnid;
  (void)env;
  mdbx_coherent_barrier();
}

static __inline void mdbx_meta_update_end(const MDBX_env *env, MDBX_meta *meta,
                                          txnid_t txnid) {
  mdbx_assert(env, meta >= METAPAGE(env, 0) || meta < METAPAGE_END(env));
  mdbx_assert(env, meta->mm_txnid_a == txnid);
  mdbx_assert(env, meta->mm_txnid_b < txnid);

  mdbx_jitter4testing(true);
  meta->mm_txnid_b = txnid;
  mdbx_coherent_barrier();
}

static __inline void mdbx_meta_set_txnid(const MDBX_env *env, MDBX_meta *meta,
                                         txnid_t txnid) {
  mdbx_assert(env, meta < METAPAGE(env, 0) || meta > METAPAGE_END(env));
  meta->mm_txnid_a = txnid;
  meta->mm_txnid_b = txnid;
}

static __inline uint64_t mdbx_meta_sign(const MDBX_meta *meta) {
  uint64_t sign = MDBX_DATASIGN_NONE;
#if 0 /* TODO */
  sign = hippeus_hash64(...);
#else
  (void)meta;
#endif
  /* LY: newer returns MDBX_DATASIGN_NONE or MDBX_DATASIGN_WEAK */
  return (sign > MDBX_DATASIGN_WEAK) ? sign : ~sign;
}

enum meta_choise_mode { prefer_last, prefer_noweak, prefer_steady };

static __inline bool mdbx_meta_ot(const enum meta_choise_mode mode,
                                  const MDBX_env *env, const MDBX_meta *a,
                                  const MDBX_meta *b) {
  mdbx_jitter4testing(true);
  txnid_t txnid_a = mdbx_meta_txnid_fluid(env, a);
  txnid_t txnid_b = mdbx_meta_txnid_fluid(env, b);
  if (txnid_a == txnid_b)
    return META_IS_STEADY(b) || (META_IS_WEAK(a) && !META_IS_WEAK(a));

  mdbx_jitter4testing(true);
  switch (mode) {
  default:
    assert(false);
  /* fall through */
  case prefer_steady:
    if (META_IS_STEADY(a) != META_IS_STEADY(b))
      return META_IS_STEADY(b);
  /* fall through */
  case prefer_noweak:
    if (META_IS_WEAK(a) != META_IS_WEAK(b))
      return !META_IS_WEAK(b);
  /* fall through */
  case prefer_last:
    mdbx_jitter4testing(true);
    return txnid_a < txnid_b;
  }
}

static __inline bool mdbx_meta_eq(const MDBX_env *env, const MDBX_meta *a,
                                  const MDBX_meta *b) {
  mdbx_jitter4testing(true);
  const txnid_t txnid = mdbx_meta_txnid_fluid(env, a);
  if (!txnid || txnid != mdbx_meta_txnid_fluid(env, b))
    return false;

  mdbx_jitter4testing(true);
  if (META_IS_STEADY(a) != META_IS_STEADY(b))
    return false;

  mdbx_jitter4testing(true);
  return true;
}

static int mdbx_meta_eq_mask(const MDBX_env *env) {
  MDBX_meta *m0 = METAPAGE(env, 0);
  MDBX_meta *m1 = METAPAGE(env, 1);
  MDBX_meta *m2 = METAPAGE(env, 2);

  int rc = mdbx_meta_eq(env, m0, m1) ? 1 : 0;
  if (mdbx_meta_eq(env, m1, m2))
    rc += 2;
  if (mdbx_meta_eq(env, m2, m0))
    rc += 4;
  return rc;
}

static __inline MDBX_meta *mdbx_meta_recent(const enum meta_choise_mode mode,
                                            const MDBX_env *env, MDBX_meta *a,
                                            MDBX_meta *b) {
  const bool a_older_that_b = mdbx_meta_ot(mode, env, a, b);
  mdbx_assert(env, !mdbx_meta_eq(env, a, b));
  return a_older_that_b ? b : a;
}

static __inline MDBX_meta *mdbx_meta_ancient(const enum meta_choise_mode mode,
                                             const MDBX_env *env, MDBX_meta *a,
                                             MDBX_meta *b) {
  const bool a_older_that_b = mdbx_meta_ot(mode, env, a, b);
  mdbx_assert(env, !mdbx_meta_eq(env, a, b));
  return a_older_that_b ? a : b;
}

static __inline MDBX_meta *
mdbx_meta_mostrecent(const enum meta_choise_mode mode, const MDBX_env *env) {
  MDBX_meta *m0 = METAPAGE(env, 0);
  MDBX_meta *m1 = METAPAGE(env, 1);
  MDBX_meta *m2 = METAPAGE(env, 2);

  MDBX_meta *head = mdbx_meta_recent(mode, env, m0, m1);
  head = mdbx_meta_recent(mode, env, head, m2);
  return head;
}

static __hot MDBX_meta *mdbx_meta_steady(const MDBX_env *env) {
  return mdbx_meta_mostrecent(prefer_steady, env);
}

static __hot MDBX_meta *mdbx_meta_head(const MDBX_env *env) {
  return mdbx_meta_mostrecent(prefer_last, env);
}

static __hot txnid_t mdbx_reclaiming_detent(const MDBX_env *env) {
  if (F_ISSET(env->me_flags, MDBX_UTTERLY_NOSYNC))
    return env->me_txn->mt_txnid - 1;

  return mdbx_meta_txnid_stable(env, mdbx_meta_steady(env));
}

static const char *mdbx_durable_str(const MDBX_meta *const meta) {
  if (META_IS_WEAK(meta))
    return "Weak";
  if (META_IS_STEADY(meta))
    return (meta->mm_datasync_sign == mdbx_meta_sign(meta)) ? "Steady"
                                                            : "Tainted";
  return "Legacy";
}

/*----------------------------------------------------------------------------*/

/* Find oldest txnid still referenced. */
static txnid_t mdbx_find_oldest(MDBX_txn *txn) {
  mdbx_tassert(txn, (txn->mt_flags & MDBX_RDONLY) == 0);
  const MDBX_env *env = txn->mt_env;
  MDBX_lockinfo *const lck = env->me_lck;

  txnid_t oldest = mdbx_reclaiming_detent(env);
  mdbx_tassert(txn, oldest <= txn->mt_txnid - 1);
  const txnid_t last_oldest = lck->mti_oldest;
  mdbx_tassert(txn, oldest >= last_oldest);
  if (last_oldest == oldest ||
      lck->mti_reader_finished_flag == MDBX_STRING_TETRAD("None"))
    return last_oldest;

  const unsigned snap_nreaders = lck->mti_numreaders;
  lck->mti_reader_finished_flag = MDBX_STRING_TETRAD("None");
  for (unsigned i = 0; i < snap_nreaders; ++i) {
    if (lck->mti_readers[i].mr_pid) {
      /* mdbx_jitter4testing(true); */
      const txnid_t snap = lck->mti_readers[i].mr_txnid;
      if (oldest > snap && last_oldest <= /* ignore pending updates */ snap) {
        oldest = snap;
        if (oldest == last_oldest)
          break;
      }
    }
  }

  if (oldest != last_oldest) {
    mdbx_notice("update oldest %" PRIaTXN " -> %" PRIaTXN, last_oldest, oldest);
    mdbx_tassert(txn, oldest >= lck->mti_oldest);
    lck->mti_oldest = oldest;
  }
  return oldest;
}

/* Add a page to the txn's dirty list */
static void mdbx_page_dirty(MDBX_txn *txn, MDBX_page *mp) {
  MDBX_ID2 mid;
  int rc, (*insert)(MDBX_ID2L, MDBX_ID2 *);

  if (txn->mt_flags & MDBX_TXN_WRITEMAP) {
    insert = mdbx_mid2l_append;
  } else {
    insert = mdbx_mid2l_insert;
  }
  mid.mid = mp->mp_pgno;
  mid.mptr = mp;
  rc = insert(txn->mt_rw_dirtylist, &mid);
  mdbx_tassert(txn, rc == 0);
  txn->mt_dirtyroom--;
}

static int mdbx_mapresize(MDBX_env *env, const pgno_t size_pgno,
                          const pgno_t limit_pgno) {
#ifdef USE_VALGRIND
  const size_t prev_mapsize = env->me_mapsize;
  void *const prev_mapaddr = env->me_map;
#endif

  const size_t limit_bytes = pgno_align2os_bytes(env, limit_pgno);
  const size_t size_bytes = pgno_align2os_bytes(env, size_pgno);

  mdbx_info("resize datafile/mapping: "
            "present %" PRIuPTR " -> %" PRIuPTR ", "
            "limit %" PRIuPTR " -> %" PRIuPTR,
            env->me_dbgeo.now, size_bytes, env->me_dbgeo.upper, limit_bytes);

  mdbx_assert(env, limit_bytes >= size_bytes);
  mdbx_assert(env, bytes2pgno(env, size_bytes) == size_pgno);
  mdbx_assert(env, bytes2pgno(env, limit_bytes) == limit_pgno);
  const int rc =
      mdbx_mresize(env->me_flags, &env->me_dxb_mmap, size_bytes, limit_bytes);

  if (rc == MDBX_SUCCESS) {
    if (env->me_txn) {
      mdbx_tassert(env->me_txn, size_pgno >= env->me_txn->mt_next_pgno);
      env->me_txn->mt_end_pgno = size_pgno;
    }
    env->me_dbgeo.now = size_bytes;
    env->me_dbgeo.upper = limit_bytes;
  } else {
    mdbx_error("failed resize datafile/mapping: "
               "present %" PRIuPTR " -> %" PRIuPTR ", "
               "limit %" PRIuPTR " -> %" PRIuPTR ", errcode %d",
               env->me_dbgeo.now, size_bytes, env->me_dbgeo.upper, limit_bytes,
               rc);
  }

#ifdef USE_VALGRIND
  if (prev_mapsize != env->me_mapsize || prev_mapaddr != env->me_map) {
    VALGRIND_DISCARD(env->me_valgrind_handle);
    env->me_valgrind_handle = 0;
    if (env->me_mapsize)
      env->me_valgrind_handle =
          VALGRIND_CREATE_BLOCK(env->me_map, env->me_mapsize, "mdbx");
  }
#endif
  return rc;
}

/* Allocate page numbers and memory for writing.  Maintain me_last_reclaimed,
 * me_reclaimed_pglist and mt_next_pgno.  Set MDBX_TXN_ERROR on failure.
 *
 * If there are free pages available from older transactions, they
 * are re-used first. Otherwise allocate a new page at mt_next_pgno.
 * Do not modify the freedB, just merge freeDB records into me_reclaimed_pglist
 * and move me_last_reclaimed to say which records were consumed.  Only this
 * function can create me_reclaimed_pglist and move
 * me_last_reclaimed/mt_next_pgno.
 *
 * [in] mc    cursor A cursor handle identifying the transaction and
 *            database for which we are allocating.
 * [in] num   the number of pages to allocate.
 * [out] mp   Address of the allocated page(s). Requests for multiple pages
 *            will always be satisfied by a single contiguous chunk of memory.
 *
 * Returns 0 on success, non-zero on failure.*/

#define MDBX_ALLOC_CACHE 1
#define MDBX_ALLOC_GC 2
#define MDBX_ALLOC_NEW 4
#define MDBX_ALLOC_KICK 8
#define MDBX_ALLOC_ALL                                                         \
  (MDBX_ALLOC_CACHE | MDBX_ALLOC_GC | MDBX_ALLOC_NEW | MDBX_ALLOC_KICK)

static int mdbx_page_alloc(MDBX_cursor *mc, unsigned num, MDBX_page **mp,
                           int flags) {
  int rc;
  MDBX_txn *txn = mc->mc_txn;
  MDBX_env *env = txn->mt_env;
  MDBX_page *np;

  if (likely(flags & MDBX_ALLOC_GC)) {
    flags |= env->me_flags & (MDBX_COALESCE | MDBX_LIFORECLAIM);
    if (unlikely(mc->mc_flags & C_RECLAIMING)) {
      /* If mc is updating the freeDB, then the freelist cannot play
       * catch-up with itself by growing while trying to save it. */
      flags &=
          ~(MDBX_ALLOC_GC | MDBX_ALLOC_KICK | MDBX_COALESCE | MDBX_LIFORECLAIM);
    }
  }

  if (likely(flags & MDBX_ALLOC_CACHE)) {
    /* If there are any loose pages, just use them */
    assert(mp && num);
    if (likely(num == 1 && txn->mt_loose_pages)) {
      np = txn->mt_loose_pages;
      txn->mt_loose_pages = NEXT_LOOSE_PAGE(np);
      txn->mt_loose_count--;
      mdbx_debug("db %d use loose page %" PRIaPGNO, DDBI(mc), np->mp_pgno);
      ASAN_UNPOISON_MEMORY_REGION(np, env->me_psize);
      *mp = np;
      return MDBX_SUCCESS;
    }
  }

  pgno_t pgno, *repg_list = env->me_reclaimed_pglist;
  unsigned repg_pos = 0, repg_len = repg_list ? repg_list[0] : 0;
  txnid_t oldest = 0, last = 0;
  const unsigned wanna_range = num - 1;

  while (1) { /* oom-kick retry loop */
    /* If our dirty list is already full, we can't do anything */
    if (unlikely(txn->mt_dirtyroom == 0)) {
      rc = MDBX_TXN_FULL;
      goto fail;
    }

    MDBX_cursor recur;
    for (MDBX_cursor_op op = MDBX_FIRST;;
         op = (flags & MDBX_LIFORECLAIM) ? MDBX_PREV : MDBX_NEXT) {
      MDBX_val key, data;

      /* Seek a big enough contiguous page range. Prefer
       * pages at the tail, just truncating the list. */
      if (likely(flags & MDBX_ALLOC_CACHE) && repg_len > wanna_range &&
          (!(flags & MDBX_COALESCE) || op == MDBX_FIRST)) {
        repg_pos = repg_len;
        do {
          pgno = repg_list[repg_pos];
          if (likely(repg_list[repg_pos - wanna_range] == pgno + wanna_range))
            goto done;
        } while (--repg_pos > wanna_range);
      }

      if (op == MDBX_FIRST) { /* 1st iteration, setup cursor, etc */
        if (unlikely(!(flags & MDBX_ALLOC_GC)))
          break /* reclaiming is prohibited for now */;

        /* Prepare to fetch more and coalesce */
        oldest = (flags & MDBX_LIFORECLAIM) ? mdbx_find_oldest(txn)
                                            : env->me_oldest[0];
        mdbx_cursor_init(&recur, txn, FREE_DBI, NULL);
        if (flags & MDBX_LIFORECLAIM) {
          /* Begin from oldest reader if any */
          if (oldest > 2) {
            last = oldest - 1;
            op = MDBX_SET_RANGE;
          }
        } else if (env->me_last_reclaimed) {
          /* Continue lookup from env->me_last_reclaimed to oldest reader */
          last = env->me_last_reclaimed;
          op = MDBX_SET_RANGE;
        }

        key.iov_base = &last;
        key.iov_len = sizeof(last);
      }

      if (!(flags & MDBX_LIFORECLAIM)) {
        /* Do not try fetch more if the record will be too recent */
        if (op != MDBX_FIRST && ++last >= oldest) {
          oldest = mdbx_find_oldest(txn);
          if (oldest <= last)
            break;
        }
      }

      rc = mdbx_cursor_get(&recur, &key, NULL, op);
      if (rc == MDBX_NOTFOUND && (flags & MDBX_LIFORECLAIM)) {
        if (op == MDBX_SET_RANGE)
          continue;
        if (oldest < mdbx_find_oldest(txn)) {
          oldest = *env->me_oldest;
          last = oldest - 1;
          key.iov_base = &last;
          key.iov_len = sizeof(last);
          op = MDBX_SET_RANGE;
          rc = mdbx_cursor_get(&recur, &key, NULL, op);
        }
      }
      if (unlikely(rc)) {
        if (rc == MDBX_NOTFOUND)
          break;
        goto fail;
      }

      last = *(txnid_t *)key.iov_base;
      if (oldest <= last) {
        oldest = mdbx_find_oldest(txn);
        if (oldest <= last) {
          if (flags & MDBX_LIFORECLAIM)
            continue;
          break;
        }
      }

      if (flags & MDBX_LIFORECLAIM) {
        /* skip IDs of records that already reclaimed */
        if (txn->mt_lifo_reclaimed) {
          unsigned i;
          for (i = (unsigned)txn->mt_lifo_reclaimed[0]; i > 0; --i)
            if (txn->mt_lifo_reclaimed[i] == last)
              break;
          if (i)
            continue;
        }
      }

      /* Reading next FreeDB record */
      np = recur.mc_pg[recur.mc_top];
      MDBX_node *leaf = NODEPTR(np, recur.mc_ki[recur.mc_top]);
      if (unlikely((rc = mdbx_node_read(&recur, leaf, &data)) != MDBX_SUCCESS))
        goto fail;

      if ((flags & MDBX_LIFORECLAIM) && !txn->mt_lifo_reclaimed) {
        txn->mt_lifo_reclaimed = mdbx_txl_alloc();
        if (unlikely(!txn->mt_lifo_reclaimed)) {
          rc = MDBX_ENOMEM;
          goto fail;
        }
      }

      /* Append PNL from FreeDB record to me_reclaimed_pglist */
      pgno_t *re_pnl = (pgno_t *)data.iov_base;
      mdbx_tassert(txn, re_pnl[0] == 0 ||
                            data.iov_len == (re_pnl[0] + 1) * sizeof(pgno_t));
      mdbx_tassert(txn, mdbx_pnl_check(re_pnl));
      repg_pos = re_pnl[0];
      if (!repg_list) {
        if (unlikely(!(env->me_reclaimed_pglist = repg_list =
                           mdbx_pnl_alloc(repg_pos)))) {
          rc = MDBX_ENOMEM;
          goto fail;
        }
      } else {
        if (unlikely(
                (rc = mdbx_pnl_need(&env->me_reclaimed_pglist, repg_pos)) != 0))
          goto fail;
        repg_list = env->me_reclaimed_pglist;
      }

      /* Remember ID of FreeDB record */
      if (flags & MDBX_LIFORECLAIM) {
        if ((rc = mdbx_txl_append(&txn->mt_lifo_reclaimed, last)) != 0)
          goto fail;
      }
      env->me_last_reclaimed = last;

      if (mdbx_debug_enabled(MDBX_DBG_EXTRA)) {
        mdbx_debug_extra("PNL read txn %" PRIaTXN " root %" PRIaPGNO
                         " num %u, PNL",
                         last, txn->mt_dbs[FREE_DBI].md_root, repg_pos);
        unsigned i;
        for (i = repg_pos; i; i--)
          mdbx_debug_extra_print(" %" PRIaPGNO "", re_pnl[i]);
        mdbx_debug_extra_print("\n");
      }

      /* Merge in descending sorted order */
      mdbx_pnl_xmerge(repg_list, re_pnl);
      repg_len = repg_list[0];

      if (unlikely((flags & MDBX_ALLOC_CACHE) == 0)) {
        /* Done for a kick-reclaim mode, actually no page needed */
        return MDBX_SUCCESS;
      }

      /* Return suitable pages into "unallocated" pull */
      while (repg_len > wanna_range &&
             repg_list[repg_len] == txn->mt_next_pgno - 1) {
        txn->mt_next_pgno -= 1;
        repg_len -= 1;
        repg_list[0] = repg_len;
      }

      /* Don't try to coalesce too much. */
      if (repg_len > MDBX_PNL_UM_SIZE / 2)
        break;
      if (flags & MDBX_COALESCE) {
        if (repg_len /* current size */ >= env->me_maxfree_1pg / 2 ||
            repg_pos /* prev size */ >= env->me_maxfree_1pg / 4)
          flags &= ~MDBX_COALESCE;
      }
    }

    if ((flags & (MDBX_COALESCE | MDBX_ALLOC_CACHE)) ==
            (MDBX_COALESCE | MDBX_ALLOC_CACHE) &&
        repg_len > wanna_range) {
      repg_pos = repg_len;
      do {
        pgno = repg_list[repg_pos];
        if (repg_list[repg_pos - wanna_range] == pgno + wanna_range)
          goto done;
      } while (--repg_pos > wanna_range);
    }

    /* Use new pages from the map when nothing suitable in the freeDB */
    repg_pos = 0;
    pgno = txn->mt_next_pgno;
    rc = MDBX_MAP_FULL;
    const pgno_t next = pgno_add(pgno, num);
    if (likely(next <= txn->mt_end_pgno)) {
      rc = MDBX_NOTFOUND;
      if (likely(flags & MDBX_ALLOC_NEW))
        goto done;
    }

    const MDBX_meta *head = mdbx_meta_head(env);
    if ((flags & MDBX_ALLOC_GC) &&
        ((flags & MDBX_ALLOC_KICK) || rc == MDBX_MAP_FULL)) {
      MDBX_meta *steady = mdbx_meta_steady(env);

      if (oldest == mdbx_meta_txnid_stable(env, steady) &&
          !META_IS_STEADY(head) && META_IS_STEADY(steady)) {
        /* LY: Here an oom was happened:
         *  - all pages had allocated;
         *  - reclaiming was stopped at the last steady-sync;
         *  - the head-sync is weak.
         * Now we need make a sync to resume reclaiming. If both
         * MDBX_NOSYNC and MDBX_MAPASYNC flags are set, then assume that
         * utterly no-sync write mode was requested. In such case
         * don't make a steady-sync, but only a legacy-mode checkpoint,
         * just for resume reclaiming only, not for data consistency. */

        mdbx_debug("kick-gc: head %" PRIaTXN "-%s, tail %" PRIaTXN
                   "-%s, oldest %" PRIaTXN "",
                   mdbx_meta_txnid_stable(env, head), mdbx_durable_str(head),
                   mdbx_meta_txnid_stable(env, steady),
                   mdbx_durable_str(steady), oldest);

        const unsigned syncflags = F_ISSET(env->me_flags, MDBX_UTTERLY_NOSYNC)
                                       ? env->me_flags
                                       : env->me_flags & MDBX_WRITEMAP;
        MDBX_meta meta = *head;
        if (mdbx_sync_locked(env, syncflags, &meta) == MDBX_SUCCESS) {
          txnid_t snap = mdbx_find_oldest(txn);
          if (snap > oldest)
            continue;
        }
      }

      if (rc == MDBX_MAP_FULL && oldest < txn->mt_txnid - 1) {
        if (mdbx_oomkick(env, oldest) > oldest)
          continue;
      }
    }

    if (rc == MDBX_MAP_FULL && next < head->mm_geo.upper) {
      mdbx_assert(env, next > txn->mt_end_pgno);
      pgno_t aligned = pgno_align2os_pgno(
          env, pgno_add(next, head->mm_geo.grow - next % head->mm_geo.grow));

      if (aligned > head->mm_geo.upper)
        aligned = head->mm_geo.upper;
      mdbx_assert(env, aligned > txn->mt_end_pgno);

      mdbx_info("try growth datafile to %" PRIaPGNO " pages (+%" PRIaPGNO ")",
                aligned, aligned - txn->mt_end_pgno);
      rc = mdbx_mapresize(env, aligned, head->mm_geo.upper);
      if (rc == MDBX_SUCCESS) {
        mdbx_tassert(env->me_txn, txn->mt_end_pgno >= next);
        if (!mp)
          return rc;
        goto done;
      }

      mdbx_warning("unable growth datafile to %" PRIaPGNO "pages (+%" PRIaPGNO
                   "), errcode %d",
                   aligned, aligned - txn->mt_end_pgno, rc);
    }

  fail:
    if (mp) {
      *mp = NULL;
      txn->mt_flags |= MDBX_TXN_ERROR;
    }
    assert(rc);
    return rc;
  }

done:
  mdbx_tassert(txn, mp && num);
  if (env->me_flags & MDBX_WRITEMAP) {
    np = pgno2page(env, pgno);
    /* LY: reset no-access flag from mdbx_kill_page() */
    VALGRIND_MAKE_MEM_UNDEFINED(np, pgno2bytes(env, num));
    ASAN_UNPOISON_MEMORY_REGION(np, pgno2bytes(env, num));
  } else {
    if (unlikely(!(np = mdbx_page_malloc(txn, num)))) {
      rc = MDBX_ENOMEM;
      goto fail;
    }
  }

  if (repg_pos) {
    /* Cutoff allocated pages from me_reclaimed_pglist */
    repg_list[0] = repg_len -= num;
    for (unsigned i = repg_pos - num; i < repg_len;)
      repg_list[++i] = repg_list[++repg_pos];
  } else {
    txn->mt_next_pgno = pgno + num;
    mdbx_assert(env, txn->mt_next_pgno <= txn->mt_end_pgno);
  }

  if (env->me_flags & MDBX_PAGEPERTURB)
    memset(np, 0x71 /* 'q', 113 */, pgno2bytes(env, num));
  VALGRIND_MAKE_MEM_UNDEFINED(np, pgno2bytes(env, num));

  np->mp_pgno = pgno;
  np->mp_leaf2_ksize = 0;
  np->mp_flags = 0;
  np->mp_pages = num;
  mdbx_page_dirty(txn, np);
  *mp = np;

  return MDBX_SUCCESS;
}

/* Copy the used portions of a non-overflow page.
 * [in] dst page to copy into
 * [in] src page to copy from
 * [in] psize size of a page */
static void mdbx_page_copy(MDBX_page *dst, MDBX_page *src, unsigned psize) {
  STATIC_ASSERT(UINT16_MAX > MAX_PAGESIZE - PAGEHDRSZ);
  STATIC_ASSERT(MIN_PAGESIZE > PAGEHDRSZ + NODESIZE * 42);
  enum { Align = sizeof(pgno_t) };
  indx_t upper = src->mp_upper, lower = src->mp_lower, unused = upper - lower;

  /* If page isn't full, just copy the used portion. Adjust
   * alignment so memcpy may copy words instead of bytes. */
  if ((unused &= -Align) && !IS_LEAF2(src)) {
    upper = (upper + PAGEHDRSZ) & -Align;
    memcpy(dst, src, (lower + PAGEHDRSZ + (Align - 1)) & -Align);
    memcpy((pgno_t *)((char *)dst + upper), (pgno_t *)((char *)src + upper),
           psize - upper);
  } else {
    memcpy(dst, src, psize - unused);
  }
}

/* Pull a page off the txn's spill list, if present.
 *
 * If a page being referenced was spilled to disk in this txn, bring
 * it back and make it dirty/writable again.
 *
 * [in] txn   the transaction handle.
 * [in] mp    the page being referenced. It must not be dirty.
 * [out] ret  the writable page, if any.
 *            ret is unchanged if mp wasn't spilled. */
static int mdbx_page_unspill(MDBX_txn *txn, MDBX_page *mp, MDBX_page **ret) {
  MDBX_env *env = txn->mt_env;
  const MDBX_txn *tx2;
  unsigned x;
  pgno_t pgno = mp->mp_pgno, pn = pgno << 1;

  for (tx2 = txn; tx2; tx2 = tx2->mt_parent) {
    if (!tx2->mt_spill_pages)
      continue;
    x = mdbx_pnl_search(tx2->mt_spill_pages, pn);
    if (x <= tx2->mt_spill_pages[0] && tx2->mt_spill_pages[x] == pn) {
      MDBX_page *np;
      int num;
      if (txn->mt_dirtyroom == 0)
        return MDBX_TXN_FULL;
      num = IS_OVERFLOW(mp) ? mp->mp_pages : 1;
      if (env->me_flags & MDBX_WRITEMAP) {
        np = mp;
      } else {
        np = mdbx_page_malloc(txn, num);
        if (unlikely(!np))
          return MDBX_ENOMEM;
        if (unlikely(num > 1))
          memcpy(np, mp, pgno2bytes(env, num));
        else
          mdbx_page_copy(np, mp, env->me_psize);
      }
      mdbx_debug("unspill page %" PRIaPGNO, mp->mp_pgno);
      if (tx2 == txn) {
        /* If in current txn, this page is no longer spilled.
         * If it happens to be the last page, truncate the spill list.
         * Otherwise mark it as deleted by setting the LSB. */
        if (x == txn->mt_spill_pages[0])
          txn->mt_spill_pages[0]--;
        else
          txn->mt_spill_pages[x] |= 1;
      } /* otherwise, if belonging to a parent txn, the
         * page remains spilled until child commits */

      mdbx_page_dirty(txn, np);
      np->mp_flags |= P_DIRTY;
      *ret = np;
      break;
    }
  }
  return MDBX_SUCCESS;
}

/* Touch a page: make it dirty and re-insert into tree with updated pgno.
 * Set MDBX_TXN_ERROR on failure.
 *
 * [in] mc  cursor pointing to the page to be touched
 *
 * Returns 0 on success, non-zero on failure. */
static int mdbx_page_touch(MDBX_cursor *mc) {
  MDBX_page *mp = mc->mc_pg[mc->mc_top], *np;
  MDBX_txn *txn = mc->mc_txn;
  MDBX_cursor *m2, *m3;
  pgno_t pgno;
  int rc;

  mdbx_cassert(mc, !IS_OVERFLOW(mp));
  if (!F_ISSET(mp->mp_flags, P_DIRTY)) {
    if (txn->mt_flags & MDBX_TXN_SPILLS) {
      np = NULL;
      rc = mdbx_page_unspill(txn, mp, &np);
      if (unlikely(rc))
        goto fail;
      if (likely(np))
        goto done;
    }

    if (unlikely((rc = mdbx_pnl_need(&txn->mt_befree_pages, 1)) ||
                 (rc = mdbx_page_alloc(mc, 1, &np, MDBX_ALLOC_ALL))))
      goto fail;
    pgno = np->mp_pgno;
    mdbx_debug("touched db %d page %" PRIaPGNO " -> %" PRIaPGNO, DDBI(mc),
               mp->mp_pgno, pgno);
    mdbx_cassert(mc, mp->mp_pgno != pgno);
    mdbx_pnl_xappend(txn->mt_befree_pages, mp->mp_pgno);
    /* Update the parent page, if any, to point to the new page */
    if (mc->mc_top) {
      MDBX_page *parent = mc->mc_pg[mc->mc_top - 1];
      MDBX_node *node = NODEPTR(parent, mc->mc_ki[mc->mc_top - 1]);
      SETPGNO(node, pgno);
    } else {
      mc->mc_db->md_root = pgno;
    }
  } else if (txn->mt_parent && !IS_SUBP(mp)) {
    MDBX_ID2 mid, *dl = txn->mt_rw_dirtylist;
    pgno = mp->mp_pgno;
    /* If txn has a parent, make sure the page is in our dirty list. */
    if (dl[0].mid) {
      unsigned x = mdbx_mid2l_search(dl, pgno);
      if (x <= dl[0].mid && dl[x].mid == pgno) {
        if (unlikely(mp != dl[x].mptr)) { /* bad cursor? */
          mdbx_error("wrong page 0x%p #%" PRIaPGNO
                     " in the dirtylist[%d], expecting %p",
                     dl[x].mptr, pgno, x, mp);
          mc->mc_flags &= ~(C_INITIALIZED | C_EOF);
          txn->mt_flags |= MDBX_TXN_ERROR;
          return MDBX_PROBLEM;
        }
        return MDBX_SUCCESS;
      }
    }

    mdbx_debug("clone db %d page %" PRIaPGNO, DDBI(mc), mp->mp_pgno);
    mdbx_cassert(mc, dl[0].mid < MDBX_PNL_UM_MAX);
    /* No - copy it */
    np = mdbx_page_malloc(txn, 1);
    if (unlikely(!np))
      return MDBX_ENOMEM;
    mid.mid = pgno;
    mid.mptr = np;
    rc = mdbx_mid2l_insert(dl, &mid);
    mdbx_cassert(mc, rc == 0);
  } else {
    return MDBX_SUCCESS;
  }

  mdbx_page_copy(np, mp, txn->mt_env->me_psize);
  np->mp_pgno = pgno;
  np->mp_flags |= P_DIRTY;

done:
  /* Adjust cursors pointing to mp */
  mc->mc_pg[mc->mc_top] = np;
  m2 = txn->mt_cursors[mc->mc_dbi];
  if (mc->mc_flags & C_SUB) {
    for (; m2; m2 = m2->mc_next) {
      m3 = &m2->mc_xcursor->mx_cursor;
      if (m3->mc_snum < mc->mc_snum)
        continue;
      if (m3->mc_pg[mc->mc_top] == mp)
        m3->mc_pg[mc->mc_top] = np;
    }
  } else {
    for (; m2; m2 = m2->mc_next) {
      if (m2->mc_snum < mc->mc_snum)
        continue;
      if (m2 == mc)
        continue;
      if (m2->mc_pg[mc->mc_top] == mp) {
        m2->mc_pg[mc->mc_top] = np;
        if (XCURSOR_INITED(m2) && IS_LEAF(np))
          XCURSOR_REFRESH(m2, np, m2->mc_ki[mc->mc_top]);
      }
    }
  }
  return MDBX_SUCCESS;

fail:
  txn->mt_flags |= MDBX_TXN_ERROR;
  return rc;
}

int mdbx_env_sync(MDBX_env *env, int force) {
  if (unlikely(!env))
    return MDBX_EINVAL;

  if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
    return MDBX_EBADSIGN;

  unsigned flags = env->me_flags & ~MDBX_NOMETASYNC;
  if (unlikely(flags & (MDBX_RDONLY | MDBX_FATAL_ERROR)))
    return MDBX_EACCESS;

  if (unlikely(!env->me_lck))
    return MDBX_PANIC;

  const bool outside_txn =
      (!env->me_txn0 || env->me_txn0->mt_owner != mdbx_thread_self());

  if (outside_txn) {
    int rc = mdbx_txn_lock(env);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  }

  MDBX_meta *head = mdbx_meta_head(env);
  if (!META_IS_STEADY(head) || env->me_sync_pending) {

    if (force || (env->me_sync_threshold &&
                  env->me_sync_pending >= env->me_sync_threshold))
      flags &= MDBX_WRITEMAP /* clear flags for full steady sync */;

    if (outside_txn &&
        env->me_sync_pending >
            pgno2bytes(env, 16 /* FIXME: define threshold */) &&
        (flags & MDBX_NOSYNC) == 0) {
      assert(((flags ^ env->me_flags) & MDBX_WRITEMAP) == 0);
      const size_t usedbytes = pgno_align2os_bytes(env, head->mm_geo.next);

      mdbx_txn_unlock(env);

      /* LY: pre-sync without holding lock to reduce latency for writer(s) */
      int rc = (flags & MDBX_WRITEMAP)
                   ? mdbx_msync(&env->me_dxb_mmap, 0, usedbytes,
                                flags & MDBX_MAPASYNC)
                   : mdbx_filesync(env->me_fd, false);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;

      rc = mdbx_txn_lock(env);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;

      /* LY: head may be changed. */
      head = mdbx_meta_head(env);
    }

    if (!META_IS_STEADY(head) || env->me_sync_pending) {
      mdbx_debug("meta-head %" PRIaPGNO ", %s, sync_pending %" PRIuPTR,
                 container_of(head, MDBX_page, mp_data)->mp_pgno,
                 mdbx_durable_str(head), env->me_sync_pending);
      MDBX_meta meta = *head;
      int rc = mdbx_sync_locked(env, flags | MDBX_SHRINK_ALLOWED, &meta);
      if (unlikely(rc != MDBX_SUCCESS)) {
        if (outside_txn)
          mdbx_txn_unlock(env);
        return rc;
      }
    }
  }

  if (outside_txn)
    mdbx_txn_unlock(env);
  return MDBX_SUCCESS;
}

/* Back up parent txn's cursors, then grab the originals for tracking */
static int mdbx_cursor_shadow(MDBX_txn *src, MDBX_txn *dst) {
  MDBX_cursor *mc, *bk;
  MDBX_xcursor *mx;
  size_t size;
  int i;

  for (i = src->mt_numdbs; --i >= 0;) {
    if ((mc = src->mt_cursors[i]) != NULL) {
      size = sizeof(MDBX_cursor);
      if (mc->mc_xcursor)
        size += sizeof(MDBX_xcursor);
      for (; mc; mc = bk->mc_next) {
        bk = malloc(size);
        if (unlikely(!bk))
          return MDBX_ENOMEM;
        *bk = *mc;
        mc->mc_backup = bk;
        mc->mc_db = &dst->mt_dbs[i];
        /* Kill pointers into src to reduce abuse: The
         * user may not use mc until dst ends. But we need a valid
         * txn pointer here for cursor fixups to keep working. */
        mc->mc_txn = dst;
        mc->mc_dbflag = &dst->mt_dbflags[i];
        if ((mx = mc->mc_xcursor) != NULL) {
          *(MDBX_xcursor *)(bk + 1) = *mx;
          mx->mx_cursor.mc_txn = dst;
        }
        mc->mc_next = dst->mt_cursors[i];
        dst->mt_cursors[i] = mc;
      }
    }
  }
  return MDBX_SUCCESS;
}

/* Close this write txn's cursors, give parent txn's cursors back to parent.
 *
 * [in] txn     the transaction handle.
 * [in] merge   true to keep changes to parent cursors, false to revert.
 *
 * Returns 0 on success, non-zero on failure. */
static void mdbx_cursors_eot(MDBX_txn *txn, unsigned merge) {
  MDBX_cursor **cursors = txn->mt_cursors, *mc, *next, *bk;
  MDBX_xcursor *mx;
  int i;

  for (i = txn->mt_numdbs; --i >= 0;) {
    for (mc = cursors[i]; mc; mc = next) {
      unsigned stage = mc->mc_signature;
      mdbx_ensure(NULL,
                  stage == MDBX_MC_SIGNATURE || stage == MDBX_MC_WAIT4EOT);
      next = mc->mc_next;
      if ((bk = mc->mc_backup) != NULL) {
        if (merge) {
          /* Commit changes to parent txn */
          mc->mc_next = bk->mc_next;
          mc->mc_backup = bk->mc_backup;
          mc->mc_txn = bk->mc_txn;
          mc->mc_db = bk->mc_db;
          mc->mc_dbflag = bk->mc_dbflag;
          if ((mx = mc->mc_xcursor) != NULL)
            mx->mx_cursor.mc_txn = bk->mc_txn;
        } else {
          /* Abort nested txn */
          *mc = *bk;
          if ((mx = mc->mc_xcursor) != NULL)
            *mx = *(MDBX_xcursor *)(bk + 1);
        }
        bk->mc_signature = 0;
        free(bk);
      }
      if (stage == MDBX_MC_WAIT4EOT) {
        mc->mc_signature = 0;
        free(mc);
      } else {
        mc->mc_signature = MDBX_MC_READY4CLOSE;
        mc->mc_flags = 0 /* reset C_UNTRACK */;
      }
    }
    cursors[i] = NULL;
  }
}

/* Common code for mdbx_txn_begin() and mdbx_txn_renew(). */
static int mdbx_txn_renew0(MDBX_txn *txn, unsigned flags) {
  MDBX_env *env = txn->mt_env;
  int rc;

  if (unlikely(env->me_pid != mdbx_getpid())) {
    env->me_flags |= MDBX_FATAL_ERROR;
    return MDBX_PANIC;
  }

  pgno_t upper_pgno = 0;
  if (flags & MDBX_TXN_RDONLY) {
    txn->mt_flags = MDBX_TXN_RDONLY;
    MDBX_reader *r = txn->mt_ro_reader;
    if (likely(env->me_flags & MDBX_ENV_TXKEY)) {
      mdbx_assert(env, !(env->me_flags & MDBX_NOTLS));
      r = mdbx_thread_rthc_get(env->me_txkey);
      if (likely(r)) {
        mdbx_assert(env, r->mr_pid == env->me_pid);
        mdbx_assert(env, r->mr_tid == mdbx_thread_self());
      }
    } else {
      mdbx_assert(env, !env->me_lck || (env->me_flags & MDBX_NOTLS));
    }

    if (likely(r)) {
      if (unlikely(r->mr_pid != env->me_pid || r->mr_txnid != ~(txnid_t)0))
        return MDBX_BAD_RSLOT;
    } else if (env->me_lck) {
      unsigned slot, nreaders;
      const mdbx_pid_t pid = env->me_pid;
      const mdbx_tid_t tid = mdbx_thread_self();
      mdbx_assert(env, env->me_lck->mti_magic_and_version == MDBX_LOCK_MAGIC);
      mdbx_assert(env, env->me_lck->mti_os_and_format == MDBX_LOCK_FORMAT);

      rc = mdbx_rdt_lock(env);
      if (unlikely(MDBX_IS_ERROR(rc)))
        return rc;
      rc = MDBX_SUCCESS;

      if (unlikely(env->me_live_reader != pid)) {
        rc = mdbx_rpid_set(env);
        if (unlikely(rc != MDBX_SUCCESS)) {
          mdbx_rdt_unlock(env);
          return rc;
        }
        env->me_live_reader = pid;
      }

      while (1) {
        nreaders = env->me_lck->mti_numreaders;
        for (slot = 0; slot < nreaders; slot++)
          if (env->me_lck->mti_readers[slot].mr_pid == 0)
            break;

        if (likely(slot < env->me_maxreaders))
          break;

        rc = mdbx_reader_check0(env, true, NULL);
        if (rc != MDBX_RESULT_TRUE) {
          mdbx_rdt_unlock(env);
          return (rc == MDBX_SUCCESS) ? MDBX_READERS_FULL : rc;
        }
      }

      STATIC_ASSERT(sizeof(MDBX_reader) == MDBX_CACHELINE_SIZE);
      STATIC_ASSERT(
          offsetof(MDBX_lockinfo, mti_readers) % MDBX_CACHELINE_SIZE == 0);
      r = &env->me_lck->mti_readers[slot];
      /* Claim the reader slot, carefully since other code
       * uses the reader table un-mutexed: First reset the
       * slot, next publish it in mtb.mti_numreaders.  After
       * that, it is safe for mdbx_env_close() to touch it.
       * When it will be closed, we can finally claim it. */
      r->mr_pid = 0;
      r->mr_txnid = ~(txnid_t)0;
      r->mr_tid = tid;
      mdbx_coherent_barrier();
      if (slot == nreaders)
        env->me_lck->mti_numreaders = ++nreaders;
      if (env->me_close_readers < nreaders)
        env->me_close_readers = nreaders;
      r->mr_pid = pid;
      mdbx_rdt_unlock(env);

      if (likely(env->me_flags & MDBX_ENV_TXKEY))
        mdbx_thread_rthc_set(env->me_txkey, r);
    }

    while (1) {
      MDBX_meta *const meta = mdbx_meta_head(env);
      mdbx_jitter4testing(false);
      const txnid_t snap = mdbx_meta_txnid_fluid(env, meta);
      mdbx_jitter4testing(false);
      if (r) {
        r->mr_txnid = snap;
        mdbx_jitter4testing(false);
        mdbx_assert(env, r->mr_pid == mdbx_getpid());
        mdbx_assert(env, r->mr_tid == mdbx_thread_self());
        mdbx_assert(env, r->mr_txnid == snap);
        mdbx_coherent_barrier();
      }
      mdbx_jitter4testing(true);

      /* Snap the state from current meta-head */
      txn->mt_txnid = snap;
      txn->mt_next_pgno = meta->mm_geo.next;
      txn->mt_end_pgno = meta->mm_geo.now;
      upper_pgno = meta->mm_geo.upper;
      memcpy(txn->mt_dbs, meta->mm_dbs, CORE_DBS * sizeof(MDBX_db));
      txn->mt_canary = meta->mm_canary;

      /* LY: Retry on a race, ITS#7970. */
      mdbx_compiler_barrier();
      if (likely(meta == mdbx_meta_head(env) &&
                 snap == mdbx_meta_txnid_fluid(env, meta) &&
                 snap >= env->me_oldest[0])) {
        mdbx_jitter4testing(false);
        break;
      }
      if (env->me_lck)
        env->me_lck->mti_reader_finished_flag = true;
    }

    if (unlikely(txn->mt_txnid == 0)) {
      mdbx_error("environment corrupted by died writer, must shutdown!");
      rc = MDBX_WANNA_RECOVERY;
      goto bailout;
    }
    mdbx_assert(env, txn->mt_txnid >= *env->me_oldest);
    txn->mt_ro_reader = r;
    txn->mt_dbxs = env->me_dbxs; /* mostly static anyway */
  } else {
    /* Not yet touching txn == env->me_txn0, it may be active */
    mdbx_jitter4testing(false);
    rc = mdbx_txn_lock(env);
    if (unlikely(rc))
      return rc;

    mdbx_jitter4testing(false);
    MDBX_meta *meta = mdbx_meta_head(env);
    mdbx_jitter4testing(false);
    txn->mt_canary = meta->mm_canary;
    const txnid_t snap = mdbx_meta_txnid_stable(env, meta);
    txn->mt_txnid = snap + 1;
    if (unlikely(txn->mt_txnid < snap)) {
      mdbx_debug("txnid overflow!");
      rc = MDBX_TXN_FULL;
      goto bailout;
    }

    txn->mt_flags = flags;
    txn->mt_child = NULL;
    txn->mt_loose_pages = NULL;
    txn->mt_loose_count = 0;
    txn->mt_dirtyroom = MDBX_PNL_UM_MAX;
    txn->mt_rw_dirtylist = env->me_dirtylist;
    txn->mt_rw_dirtylist[0].mid = 0;
    txn->mt_befree_pages = env->me_free_pgs;
    txn->mt_befree_pages[0] = 0;
    txn->mt_spill_pages = NULL;
    if (txn->mt_lifo_reclaimed)
      txn->mt_lifo_reclaimed[0] = 0;
    env->me_txn = txn;
    memcpy(txn->mt_dbiseqs, env->me_dbiseqs, env->me_maxdbs * sizeof(unsigned));
    /* Copy the DB info and flags */
    memcpy(txn->mt_dbs, meta->mm_dbs, CORE_DBS * sizeof(MDBX_db));
    /* Moved to here to avoid a data race in read TXNs */
    txn->mt_next_pgno = meta->mm_geo.next;
    txn->mt_end_pgno = meta->mm_geo.now;
    upper_pgno = meta->mm_geo.upper;
  }

  /* Setup db info */
  txn->mt_numdbs = env->me_numdbs;
  for (unsigned i = CORE_DBS; i < txn->mt_numdbs; i++) {
    unsigned x = env->me_dbflags[i];
    txn->mt_dbs[i].md_flags = x & PERSISTENT_FLAGS;
    txn->mt_dbflags[i] =
        (x & MDBX_VALID) ? DB_VALID | DB_USRVALID | DB_STALE : 0;
  }
  txn->mt_dbflags[MAIN_DBI] = DB_VALID | DB_USRVALID;
  txn->mt_dbflags[FREE_DBI] = DB_VALID;

  if (unlikely(env->me_flags & MDBX_FATAL_ERROR)) {
    mdbx_warning("environment had fatal error, must shutdown!");
    rc = MDBX_PANIC;
  } else {
    const size_t size = pgno2bytes(env, txn->mt_end_pgno);
    if (unlikely(size > env->me_mapsize)) {
      if (upper_pgno > MAX_PAGENO ||
          bytes2pgno(env, pgno2bytes(env, upper_pgno)) != upper_pgno) {
        rc = MDBX_MAP_RESIZED;
        goto bailout;
      }
      rc = mdbx_mapresize(env, txn->mt_end_pgno, upper_pgno);
      if (rc != MDBX_SUCCESS)
        goto bailout;
    }
    return MDBX_SUCCESS;
  }
bailout:
  assert(rc != MDBX_SUCCESS);
  mdbx_txn_end(txn, MDBX_END_SLOT | MDBX_END_FAIL_BEGIN);
  return rc;
}

int mdbx_txn_renew(MDBX_txn *txn) {
  int rc;

  if (unlikely(!txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(!F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY | MDBX_TXN_FINISHED)))
    return MDBX_EINVAL;

  rc = mdbx_txn_renew0(txn, MDBX_TXN_RDONLY);
  if (rc == MDBX_SUCCESS) {
    mdbx_debug("renew txn %" PRIaTXN "%c %p on env %p, root page %" PRIaPGNO
               "/%" PRIaPGNO,
               txn->mt_txnid, (txn->mt_flags & MDBX_TXN_RDONLY) ? 'r' : 'w',
               (void *)txn, (void *)txn->mt_env, txn->mt_dbs[MAIN_DBI].md_root,
               txn->mt_dbs[FREE_DBI].md_root);
  }
  return rc;
}

int mdbx_txn_begin(MDBX_env *env, MDBX_txn *parent, unsigned flags,
                   MDBX_txn **ret) {
  MDBX_txn *txn;
  MDBX_ntxn *ntxn;
  int rc, size, tsize;

  if (unlikely(!env || !ret))
    return MDBX_EINVAL;

  if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(env->me_pid != mdbx_getpid())) {
    env->me_flags |= MDBX_FATAL_ERROR;
    return MDBX_PANIC;
  }

  if (unlikely(!env->me_map))
    return MDBX_EPERM;

  flags &= MDBX_TXN_BEGIN_FLAGS;
  flags |= env->me_flags & MDBX_WRITEMAP;

  if (unlikely(env->me_flags & MDBX_RDONLY &
               ~flags)) /* write txn in RDONLY env */
    return MDBX_EACCESS;

  if (parent) {
    if (unlikely(parent->mt_signature != MDBX_MT_SIGNATURE))
      return MDBX_EINVAL;

    if (unlikely(parent->mt_owner != mdbx_thread_self()))
      return MDBX_THREAD_MISMATCH;

    /* Nested transactions: Max 1 child, write txns only, no writemap */
    flags |= parent->mt_flags;
    if (unlikely(flags & (MDBX_RDONLY | MDBX_WRITEMAP | MDBX_TXN_BLOCKED))) {
      return (parent->mt_flags & MDBX_TXN_RDONLY) ? MDBX_EINVAL : MDBX_BAD_TXN;
    }
    /* Child txns save MDBX_pgstate and use own copy of cursors */
    size = env->me_maxdbs * (sizeof(MDBX_db) + sizeof(MDBX_cursor *) + 1);
    size += tsize = sizeof(MDBX_ntxn);
  } else if (flags & MDBX_RDONLY) {
    size = env->me_maxdbs * (sizeof(MDBX_db) + 1);
    size += tsize = sizeof(MDBX_txn);
  } else {
    /* Reuse preallocated write txn. However, do not touch it until
     * mdbx_txn_renew0() succeeds, since it currently may be active. */
    txn = env->me_txn0;
    goto renew;
  }
  if (unlikely((txn = calloc(1, size)) == NULL)) {
    mdbx_debug("calloc: %s", "failed");
    return MDBX_ENOMEM;
  }
  txn->mt_dbxs = env->me_dbxs; /* static */
  txn->mt_dbs = (MDBX_db *)((char *)txn + tsize);
  txn->mt_dbflags = (uint8_t *)txn + size - env->me_maxdbs;
  txn->mt_flags = flags;
  txn->mt_env = env;

  if (parent) {
    unsigned i;
    txn->mt_cursors = (MDBX_cursor **)(txn->mt_dbs + env->me_maxdbs);
    txn->mt_dbiseqs = parent->mt_dbiseqs;
    txn->mt_rw_dirtylist = malloc(sizeof(MDBX_ID2) * MDBX_PNL_UM_SIZE);
    if (!txn->mt_rw_dirtylist ||
        !(txn->mt_befree_pages = mdbx_pnl_alloc(MDBX_PNL_UM_MAX))) {
      free(txn->mt_rw_dirtylist);
      free(txn);
      return MDBX_ENOMEM;
    }
    txn->mt_txnid = parent->mt_txnid;
    txn->mt_dirtyroom = parent->mt_dirtyroom;
    txn->mt_rw_dirtylist[0].mid = 0;
    txn->mt_spill_pages = NULL;
    txn->mt_next_pgno = parent->mt_next_pgno;
    txn->mt_end_pgno = parent->mt_end_pgno;
    parent->mt_flags |= MDBX_TXN_HAS_CHILD;
    parent->mt_child = txn;
    txn->mt_parent = parent;
    txn->mt_numdbs = parent->mt_numdbs;
    memcpy(txn->mt_dbs, parent->mt_dbs, txn->mt_numdbs * sizeof(MDBX_db));
    /* Copy parent's mt_dbflags, but clear DB_NEW */
    for (i = 0; i < txn->mt_numdbs; i++)
      txn->mt_dbflags[i] = parent->mt_dbflags[i] & ~DB_NEW;
    rc = 0;
    ntxn = (MDBX_ntxn *)txn;
    ntxn->mnt_pgstate =
        env->me_pgstate; /* save parent me_reclaimed_pglist & co */
    if (env->me_reclaimed_pglist) {
      size = MDBX_PNL_SIZEOF(env->me_reclaimed_pglist);
      env->me_reclaimed_pglist = mdbx_pnl_alloc(env->me_reclaimed_pglist[0]);
      if (likely(env->me_reclaimed_pglist))
        memcpy(env->me_reclaimed_pglist, ntxn->mnt_pgstate.mf_reclaimed_pglist,
               size);
      else
        rc = MDBX_ENOMEM;
    }
    if (likely(!rc))
      rc = mdbx_cursor_shadow(parent, txn);
    if (unlikely(rc))
      mdbx_txn_end(txn, MDBX_END_FAIL_BEGINCHILD);
  } else { /* MDBX_RDONLY */
    txn->mt_dbiseqs = env->me_dbiseqs;
  renew:
    rc = mdbx_txn_renew0(txn, flags);
  }

  if (unlikely(rc)) {
    if (txn != env->me_txn0)
      free(txn);
  } else {
    txn->mt_owner = mdbx_thread_self();
    txn->mt_signature = MDBX_MT_SIGNATURE;
    *ret = txn;
    mdbx_debug("begin txn %" PRIaTXN "%c %p on env %p, root page %" PRIaPGNO
               "/%" PRIaPGNO,
               txn->mt_txnid, (flags & MDBX_RDONLY) ? 'r' : 'w', (void *)txn,
               (void *)env, txn->mt_dbs[MAIN_DBI].md_root,
               txn->mt_dbs[FREE_DBI].md_root);
  }

  return rc;
}

MDBX_env *mdbx_txn_env(MDBX_txn *txn) {
  if (unlikely(!txn || txn->mt_signature != MDBX_MT_SIGNATURE))
    return NULL;
  return txn->mt_env;
}

uint64_t mdbx_txn_id(MDBX_txn *txn) {
  if (unlikely(!txn || txn->mt_signature != MDBX_MT_SIGNATURE))
    return ~(txnid_t)0;
  return txn->mt_txnid;
}

/* Export or close DBI handles opened in this txn. */
static void mdbx_dbis_update(MDBX_txn *txn, int keep) {
  MDBX_dbi n = txn->mt_numdbs;
  if (n) {
    MDBX_env *env = txn->mt_env;
    uint8_t *tdbflags = txn->mt_dbflags;

    for (unsigned i = n; --i >= CORE_DBS;) {
      if (tdbflags[i] & DB_NEW) {
        if (keep) {
          env->me_dbflags[i] = txn->mt_dbs[i].md_flags | MDBX_VALID;
        } else {
          char *ptr = env->me_dbxs[i].md_name.iov_base;
          if (ptr) {
            env->me_dbxs[i].md_name.iov_base = NULL;
            env->me_dbxs[i].md_name.iov_len = 0;
            env->me_dbflags[i] = 0;
            env->me_dbiseqs[i]++;
            free(ptr);
          }
        }
      }
    }
    if (keep && env->me_numdbs < n)
      env->me_numdbs = n;
  }
}

/* End a transaction, except successful commit of a nested transaction.
 * May be called twice for readonly txns: First reset it, then abort.
 * [in] txn   the transaction handle to end
 * [in] mode  why and how to end the transaction */
static int mdbx_txn_end(MDBX_txn *txn, unsigned mode) {
  MDBX_env *env = txn->mt_env;
  static const char *const names[] = MDBX_END_NAMES;

  if (unlikely(txn->mt_env->me_pid != mdbx_getpid())) {
    env->me_flags |= MDBX_FATAL_ERROR;
    return MDBX_PANIC;
  }

  /* Export or close DBI handles opened in this txn */
  mdbx_dbis_update(txn, mode & MDBX_END_UPDATE);

  mdbx_debug("%s txn %" PRIaTXN "%c %p on mdbenv %p, root page %" PRIaPGNO
             "/%" PRIaPGNO,
             names[mode & MDBX_END_OPMASK], txn->mt_txnid,
             (txn->mt_flags & MDBX_TXN_RDONLY) ? 'r' : 'w', (void *)txn,
             (void *)env, txn->mt_dbs[MAIN_DBI].md_root,
             txn->mt_dbs[FREE_DBI].md_root);

  if (F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY)) {
    if (txn->mt_ro_reader) {
      txn->mt_ro_reader->mr_txnid = ~(txnid_t)0;
      env->me_lck->mti_reader_finished_flag = true;
      if (mode & MDBX_END_SLOT) {
        if ((env->me_flags & MDBX_ENV_TXKEY) == 0)
          txn->mt_ro_reader->mr_pid = 0;
        txn->mt_ro_reader = NULL;
      }
    }
    mdbx_coherent_barrier();
    txn->mt_numdbs = 0; /* prevent further DBI activity */
    txn->mt_flags |= MDBX_TXN_FINISHED;
    txn->mt_owner = 0;
  } else if (!F_ISSET(txn->mt_flags, MDBX_TXN_FINISHED)) {
    pgno_t *pghead = env->me_reclaimed_pglist;

    if (!(mode & MDBX_END_EOTDONE)) /* !(already closed cursors) */
      mdbx_cursors_eot(txn, 0);
    if (!(env->me_flags & MDBX_WRITEMAP)) {
      mdbx_dlist_free(txn);
    }

    if (txn->mt_lifo_reclaimed) {
      txn->mt_lifo_reclaimed[0] = 0;
      if (txn != env->me_txn0) {
        mdbx_txl_free(txn->mt_lifo_reclaimed);
        txn->mt_lifo_reclaimed = NULL;
      }
    }
    txn->mt_numdbs = 0;
    txn->mt_flags = MDBX_TXN_FINISHED;

    if (!txn->mt_parent) {
      mdbx_pnl_shrink(&txn->mt_befree_pages);
      env->me_free_pgs = txn->mt_befree_pages;
      /* me_pgstate: */
      env->me_reclaimed_pglist = NULL;
      env->me_last_reclaimed = 0;

      env->me_txn = NULL;
      txn->mt_owner = 0;
      txn->mt_signature = 0;
      mode = 0; /* txn == env->me_txn0, do not free() it */

      /* The writer mutex was locked in mdbx_txn_begin. */
      mdbx_txn_unlock(env);
    } else {
      txn->mt_parent->mt_child = NULL;
      txn->mt_parent->mt_flags &= ~MDBX_TXN_HAS_CHILD;
      env->me_pgstate = ((MDBX_ntxn *)txn)->mnt_pgstate;
      mdbx_pnl_free(txn->mt_befree_pages);
      mdbx_pnl_free(txn->mt_spill_pages);
      free(txn->mt_rw_dirtylist);
    }

    mdbx_pnl_free(pghead);
  }

  if (mode & MDBX_END_FREE) {
    mdbx_ensure(env, txn != env->me_txn0);
    txn->mt_owner = 0;
    txn->mt_signature = 0;
    free(txn);
  }

  return MDBX_SUCCESS;
}

int mdbx_txn_reset(MDBX_txn *txn) {
  if (unlikely(!txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  /* This call is only valid for read-only txns */
  if (unlikely(!(txn->mt_flags & MDBX_TXN_RDONLY)))
    return MDBX_EINVAL;

  /* LY: don't close DBI-handles in MDBX mode */
  return mdbx_txn_end(txn, MDBX_END_RESET | MDBX_END_UPDATE);
}

int mdbx_txn_abort(MDBX_txn *txn) {
  if (unlikely(!txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY))
    /* LY: don't close DBI-handles in MDBX mode */
    return mdbx_txn_end(txn, MDBX_END_ABORT | MDBX_END_UPDATE | MDBX_END_SLOT |
                                 MDBX_END_FREE);

  if (txn->mt_child)
    mdbx_txn_abort(txn->mt_child);

  return mdbx_txn_end(txn, MDBX_END_ABORT | MDBX_END_SLOT | MDBX_END_FREE);
}

static __inline int mdbx_backlog_size(MDBX_txn *txn) {
  int reclaimed = txn->mt_env->me_reclaimed_pglist
                      ? txn->mt_env->me_reclaimed_pglist[0]
                      : 0;
  return reclaimed + txn->mt_loose_count;
}

/* LY: Prepare a backlog of pages to modify FreeDB itself,
 * while reclaiming is prohibited. It should be enough to prevent search
 * in mdbx_page_alloc() during a deleting, when freeDB tree is unbalanced. */
static int mdbx_prep_backlog(MDBX_txn *txn, MDBX_cursor *mc) {
  /* LY: extra page(s) for b-tree rebalancing */
  const int extra = (txn->mt_env->me_flags & MDBX_LIFORECLAIM) ? 2 : 1;

  if (mdbx_backlog_size(txn) < mc->mc_db->md_depth + extra) {
    int rc = mdbx_cursor_touch(mc);
    if (unlikely(rc))
      return rc;

    while (unlikely(mdbx_backlog_size(txn) < extra)) {
      rc = mdbx_page_alloc(mc, 1, NULL, MDBX_ALLOC_GC);
      if (unlikely(rc)) {
        if (unlikely(rc != MDBX_NOTFOUND))
          return rc;
        break;
      }
    }
  }

  return MDBX_SUCCESS;
}

/* Save the freelist as of this transaction to the freeDB.
 * This changes the freelist. Keep trying until it stabilizes. */
static int mdbx_freelist_save(MDBX_txn *txn) {
  /* env->me_reclaimed_pglist[] can grow and shrink during this call.
   * env->me_last_reclaimed and txn->mt_free_pages[] can only grow.
   * Page numbers cannot disappear from txn->mt_free_pages[]. */
  MDBX_cursor mc;
  MDBX_env *env = txn->mt_env;
  int rc, more = 1;
  txnid_t cleanup_reclaimed_id = 0, head_id = 0;
  pgno_t befree_count = 0;
  intptr_t head_room = 0, total_room = 0;
  unsigned cleanup_reclaimed_pos = 0, refill_reclaimed_pos = 0;
  const bool lifo = (env->me_flags & MDBX_LIFORECLAIM) != 0;

  mdbx_cursor_init(&mc, txn, FREE_DBI, NULL);

  /* MDBX_RESERVE cancels meminit in ovpage malloc (when no WRITEMAP) */
  const intptr_t clean_limit =
      (env->me_flags & (MDBX_NOMEMINIT | MDBX_WRITEMAP)) ? SSIZE_MAX
                                                         : env->me_maxfree_1pg;

again_on_freelist_change:
  while (1) {
    /* Come back here after each Put() in case freelist changed */
    MDBX_val key, data;

    if (!lifo) {
      /* If using records from freeDB which we have not yet deleted,
       * now delete them and any we reserved for me_reclaimed_pglist. */
      while (cleanup_reclaimed_id < env->me_last_reclaimed) {
        rc = mdbx_cursor_first(&mc, &key, NULL);
        if (unlikely(rc))
          goto bailout;
        rc = mdbx_prep_backlog(txn, &mc);
        if (unlikely(rc))
          goto bailout;
        cleanup_reclaimed_id = head_id = *(txnid_t *)key.iov_base;
        total_room = head_room = 0;
        more = 1;
        mdbx_tassert(txn, cleanup_reclaimed_id <= env->me_last_reclaimed);
        mc.mc_flags |= C_RECLAIMING;
        rc = mdbx_cursor_del(&mc, 0);
        mc.mc_flags ^= C_RECLAIMING;
        if (unlikely(rc))
          goto bailout;
      }
    } else if (txn->mt_lifo_reclaimed) {
      /* LY: cleanup reclaimed records. */
      while (cleanup_reclaimed_pos < txn->mt_lifo_reclaimed[0]) {
        cleanup_reclaimed_id = txn->mt_lifo_reclaimed[++cleanup_reclaimed_pos];
        key.iov_base = &cleanup_reclaimed_id;
        key.iov_len = sizeof(cleanup_reclaimed_id);
        rc = mdbx_cursor_get(&mc, &key, NULL, MDBX_SET);
        if (likely(rc != MDBX_NOTFOUND)) {
          if (unlikely(rc))
            goto bailout;
          rc = mdbx_prep_backlog(txn, &mc);
          if (unlikely(rc))
            goto bailout;
          mc.mc_flags |= C_RECLAIMING;
          rc = mdbx_cursor_del(&mc, 0);
          mc.mc_flags ^= C_RECLAIMING;
          if (unlikely(rc))
            goto bailout;
        }
      }
    }

    if (txn->mt_loose_pages) {
      /* Return loose page numbers to me_reclaimed_pglist,
       * though usually none are left at this point.
       * The pages themselves remain in dirtylist. */
      if (unlikely(!env->me_reclaimed_pglist) &&
          !(lifo && env->me_last_reclaimed > 1)) {
        /* Put loose page numbers in mt_free_pages,
         * since unable to return them to me_reclaimed_pglist. */
        MDBX_page *mp = txn->mt_loose_pages;
        if (unlikely((rc = mdbx_pnl_need(&txn->mt_befree_pages,
                                         txn->mt_loose_count)) != 0))
          return rc;
        for (; mp; mp = NEXT_LOOSE_PAGE(mp))
          mdbx_pnl_xappend(txn->mt_befree_pages, mp->mp_pgno);
      } else {
        /* Room for loose pages + temp PNL with same */
        if ((rc = mdbx_pnl_need(&env->me_reclaimed_pglist,
                                2 * txn->mt_loose_count + 1)) != 0)
          goto bailout;
        MDBX_PNL loose = env->me_reclaimed_pglist +
                         MDBX_PNL_ALLOCLEN(env->me_reclaimed_pglist) -
                         txn->mt_loose_count;
        unsigned count = 0;
        for (MDBX_page *mp = txn->mt_loose_pages; mp; mp = NEXT_LOOSE_PAGE(mp))
          loose[++count] = mp->mp_pgno;
        loose[0] = count;
        mdbx_pnl_sort(loose);
        mdbx_pnl_xmerge(env->me_reclaimed_pglist, loose);
      }

      txn->mt_loose_pages = NULL;
      txn->mt_loose_count = 0;
    }

    /* Save the PNL of pages freed by this txn, to a single record */
    if (befree_count < txn->mt_befree_pages[0]) {
      if (unlikely(!befree_count)) {
        /* Make sure last page of freeDB is touched and on freelist */
        rc = mdbx_page_search(&mc, NULL, MDBX_PS_LAST | MDBX_PS_MODIFY);
        if (unlikely(rc && rc != MDBX_NOTFOUND))
          goto bailout;
      }
      pgno_t *befree_pages = txn->mt_befree_pages;
      /* Write to last page of freeDB */
      key.iov_len = sizeof(txn->mt_txnid);
      key.iov_base = &txn->mt_txnid;
      do {
        befree_count = befree_pages[0];
        data.iov_len = MDBX_PNL_SIZEOF(befree_pages);
        rc = mdbx_cursor_put(&mc, &key, &data, MDBX_RESERVE);
        if (unlikely(rc))
          goto bailout;
        /* Retry if mt_free_pages[] grew during the Put() */
        befree_pages = txn->mt_befree_pages;
      } while (befree_count < befree_pages[0]);

      mdbx_pnl_sort(befree_pages);
      memcpy(data.iov_base, befree_pages, data.iov_len);

      if (mdbx_debug_enabled(MDBX_DBG_EXTRA)) {
        unsigned i = (unsigned)befree_pages[0];
        mdbx_debug_extra("PNL write txn %" PRIaTXN " root %" PRIaPGNO
                         " num %u, PNL",
                         txn->mt_txnid, txn->mt_dbs[FREE_DBI].md_root, i);
        for (; i; i--)
          mdbx_debug_extra_print(" %" PRIaPGNO "", befree_pages[i]);
        mdbx_debug_extra_print("\n");
      }
      continue;
    }

    const intptr_t rpl_len =
        (env->me_reclaimed_pglist ? env->me_reclaimed_pglist[0] : 0) +
        txn->mt_loose_count;
    if (rpl_len && refill_reclaimed_pos == 0)
      refill_reclaimed_pos = 1;

    /* Reserve records for me_reclaimed_pglist[]. Split it if multi-page,
     * to avoid searching freeDB for a page range. Use keys in
     * range [1,me_last_reclaimed]: Smaller than txnid of oldest reader. */
    if (total_room >= rpl_len) {
      if (total_room == rpl_len || --more < 0)
        break;
    } else if (head_room >= (intptr_t)env->me_maxfree_1pg && head_id > 1) {
      /* Keep current record (overflow page), add a new one */
      head_id--;
      refill_reclaimed_pos++;
      head_room = 0;
    }

    if (lifo) {
      if (refill_reclaimed_pos >
          (txn->mt_lifo_reclaimed ? txn->mt_lifo_reclaimed[0] : 0)) {
        /* LY: need just a txn-id for save page list. */
        rc = mdbx_page_alloc(&mc, 0, NULL, MDBX_ALLOC_GC | MDBX_ALLOC_KICK);
        if (likely(rc == 0))
          /* LY: ok, reclaimed from freedb. */
          continue;
        if (unlikely(rc != MDBX_NOTFOUND))
          /* LY: other troubles... */
          goto bailout;

        /* LY: freedb is empty, will look any free txn-id in high2low order. */
        if (unlikely(env->me_last_reclaimed < 1)) {
          /* LY: not any txn in the past of freedb. */
          rc = MDBX_MAP_FULL;
          goto bailout;
        }

        if (unlikely(!txn->mt_lifo_reclaimed)) {
          txn->mt_lifo_reclaimed = mdbx_txl_alloc();
          if (unlikely(!txn->mt_lifo_reclaimed)) {
            rc = MDBX_ENOMEM;
            goto bailout;
          }
        }
        /* LY: append the list. */
        rc = mdbx_txl_append(&txn->mt_lifo_reclaimed,
                             env->me_last_reclaimed - 1);
        if (unlikely(rc))
          goto bailout;
        --env->me_last_reclaimed;
        /* LY: note that freeDB cleanup is not needed. */
        ++cleanup_reclaimed_pos;
      }
      mdbx_tassert(txn, txn->mt_lifo_reclaimed != NULL);
      head_id = txn->mt_lifo_reclaimed[refill_reclaimed_pos];
    } else {
      mdbx_tassert(txn, txn->mt_lifo_reclaimed == NULL);
    }

    /* (Re)write {key = head_id, PNL length = head_room} */
    total_room -= head_room;
    head_room = rpl_len - total_room;
    if (head_room > (intptr_t)env->me_maxfree_1pg && head_id > 1) {
      /* Overflow multi-page for part of me_reclaimed_pglist */
      head_room /= (head_id < INT16_MAX) ? (pgno_t)head_id
                                         : INT16_MAX; /* amortize page sizes */
      head_room += env->me_maxfree_1pg - head_room % (env->me_maxfree_1pg + 1);
    } else if (head_room < 0) {
      /* Rare case, not bothering to delete this record */
      head_room = 0;
      continue;
    }
    key.iov_len = sizeof(head_id);
    key.iov_base = &head_id;
    data.iov_len = (head_room + 1) * sizeof(pgno_t);
    rc = mdbx_cursor_put(&mc, &key, &data, MDBX_RESERVE);
    if (unlikely(rc))
      goto bailout;

    /* PNL is initially empty, zero out at least the length */
    pgno_t *pgs = (pgno_t *)data.iov_base;
    intptr_t i = head_room > clean_limit ? head_room : 0;
    do {
      pgs[i] = 0;
    } while (--i >= 0);
    total_room += head_room;
    continue;
  }

  mdbx_tassert(txn,
               cleanup_reclaimed_pos ==
                   (txn->mt_lifo_reclaimed ? txn->mt_lifo_reclaimed[0] : 0));

  /* Fill in the reserved me_reclaimed_pglist records */
  rc = MDBX_SUCCESS;
  if (env->me_reclaimed_pglist && env->me_reclaimed_pglist[0]) {
    MDBX_val key, data;
    key.iov_len = data.iov_len = 0; /* avoid MSVC warning */
    key.iov_base = data.iov_base = NULL;

    size_t rpl_left = env->me_reclaimed_pglist[0];
    pgno_t *rpl_end = env->me_reclaimed_pglist + rpl_left;
    if (txn->mt_lifo_reclaimed == 0) {
      mdbx_tassert(txn, lifo == 0);
      rc = mdbx_cursor_first(&mc, &key, &data);
      if (unlikely(rc))
        goto bailout;
    } else {
      mdbx_tassert(txn, lifo != 0);
    }

    while (1) {
      txnid_t id;
      if (txn->mt_lifo_reclaimed == 0) {
        mdbx_tassert(txn, lifo == 0);
        id = *(txnid_t *)key.iov_base;
        mdbx_tassert(txn, id <= env->me_last_reclaimed);
      } else {
        mdbx_tassert(txn, lifo != 0);
        mdbx_tassert(txn,
                     refill_reclaimed_pos > 0 &&
                         refill_reclaimed_pos <= txn->mt_lifo_reclaimed[0]);
        id = txn->mt_lifo_reclaimed[refill_reclaimed_pos--];
        key.iov_base = &id;
        key.iov_len = sizeof(id);
        rc = mdbx_cursor_get(&mc, &key, &data, MDBX_SET);
        if (unlikely(rc))
          goto bailout;
      }
      mdbx_tassert(
          txn, cleanup_reclaimed_pos ==
                   (txn->mt_lifo_reclaimed ? txn->mt_lifo_reclaimed[0] : 0));

      mdbx_tassert(txn, data.iov_len >= sizeof(pgno_t) * 2);
      size_t chunk_len = (data.iov_len / sizeof(pgno_t)) - 1;
      if (chunk_len > rpl_left)
        chunk_len = rpl_left;
      data.iov_len = (chunk_len + 1) * sizeof(pgno_t);
      key.iov_base = &id;
      key.iov_len = sizeof(id);

      rpl_end -= chunk_len;
      data.iov_base = rpl_end;
      pgno_t save = rpl_end[0];
      rpl_end[0] = (pgno_t)chunk_len;
      mdbx_tassert(txn, mdbx_pnl_check(rpl_end));
      mc.mc_flags |= C_RECLAIMING;
      rc = mdbx_cursor_put(&mc, &key, &data, MDBX_CURRENT);
      mc.mc_flags ^= C_RECLAIMING;
      mdbx_tassert(
          txn, cleanup_reclaimed_pos ==
                   (txn->mt_lifo_reclaimed ? txn->mt_lifo_reclaimed[0] : 0));
      rpl_end[0] = save;
      if (unlikely(rc))
        goto bailout;

      rpl_left -= chunk_len;
      if (rpl_left == 0)
        break;

      if (!lifo) {
        rc = mdbx_cursor_next(&mc, &key, &data, MDBX_NEXT);
        if (unlikely(rc))
          goto bailout;
      }
    }
  }

bailout:
  if (txn->mt_lifo_reclaimed) {
    mdbx_tassert(txn, rc || cleanup_reclaimed_pos == txn->mt_lifo_reclaimed[0]);
    if (rc == MDBX_SUCCESS &&
        cleanup_reclaimed_pos != txn->mt_lifo_reclaimed[0]) {
      mdbx_tassert(txn, cleanup_reclaimed_pos < txn->mt_lifo_reclaimed[0]);
      /* LY: zeroed cleanup_idx to force cleanup
       * and refill created freeDB records. */
      cleanup_reclaimed_pos = 0;
      /* LY: restart filling */
      total_room = head_room = refill_reclaimed_pos = 0;
      more = 1;
      goto again_on_freelist_change;
    }
    txn->mt_lifo_reclaimed[0] = 0;
    if (txn != env->me_txn0) {
      mdbx_txl_free(txn->mt_lifo_reclaimed);
      txn->mt_lifo_reclaimed = NULL;
    }
  }

  return rc;
}

/* Flush (some) dirty pages to the map, after clearing their dirty flag.
 * [in] txn   the transaction that's being committed
 * [in] keep  number of initial pages in dirtylist to keep dirty.
 * Returns 0 on success, non-zero on failure. */
static int mdbx_page_flush(MDBX_txn *txn, pgno_t keep) {
  MDBX_env *env = txn->mt_env;
  MDBX_ID2L dl = txn->mt_rw_dirtylist;
  unsigned i, j, pagecount = dl[0].mid;
  int rc;
  size_t size = 0, pos = 0;
  pgno_t pgno = 0;
  MDBX_page *dp = NULL;
  struct iovec iov[MDBX_COMMIT_PAGES];
  intptr_t wpos = 0, wsize = 0;
  size_t next_pos = 1; /* impossible pos, so pos != next_pos */
  int n = 0;

  j = i = keep;

  if (env->me_flags & MDBX_WRITEMAP) {
    /* Clear dirty flags */
    while (++i <= pagecount) {
      dp = dl[i].mptr;
      /* Don't flush this page yet */
      if (dp->mp_flags & (P_LOOSE | P_KEEP)) {
        dp->mp_flags &= ~P_KEEP;
        dl[++j] = dl[i];
        continue;
      }
      dp->mp_flags &= ~P_DIRTY;
      dp->mp_validator = 0 /* TODO */;
      env->me_sync_pending +=
          IS_OVERFLOW(dp) ? pgno2bytes(env, dp->mp_pages) : env->me_psize;
    }
    goto done;
  }

  /* Write the pages */
  for (;;) {
    if (++i <= pagecount) {
      dp = dl[i].mptr;
      /* Don't flush this page yet */
      if (dp->mp_flags & (P_LOOSE | P_KEEP)) {
        dp->mp_flags &= ~P_KEEP;
        dl[i].mid = 0;
        continue;
      }
      pgno = dl[i].mid;
      /* clear dirty flag */
      dp->mp_flags &= ~P_DIRTY;
      dp->mp_validator = 0 /* TODO */;
      pos = pgno2bytes(env, pgno);
      size = IS_OVERFLOW(dp) ? pgno2bytes(env, dp->mp_pages) : env->me_psize;
      env->me_sync_pending += size;
    }
    /* Write up to MDBX_COMMIT_PAGES dirty pages at a time. */
    if (pos != next_pos || n == MDBX_COMMIT_PAGES || wsize + size > MAX_WRITE) {
      if (n) {
        /* Write previous page(s) */
        rc = mdbx_pwritev(env->me_fd, iov, n, wpos, wsize);
        if (unlikely(rc != MDBX_SUCCESS)) {
          mdbx_debug("Write error: %s", strerror(rc));
          return rc;
        }
        n = 0;
      }
      if (i > pagecount)
        break;
      wpos = pos;
      wsize = 0;
    }
    mdbx_debug("committing page %" PRIaPGNO "", pgno);
    next_pos = pos + size;
    iov[n].iov_len = size;
    iov[n].iov_base = (char *)dp;
    wsize += size;
    n++;
  }

  mdbx_invalidate_cache(env->me_map, pgno2bytes(env, txn->mt_next_pgno));

  for (i = keep; ++i <= pagecount;) {
    dp = dl[i].mptr;
    /* This is a page we skipped above */
    if (!dl[i].mid) {
      dl[++j] = dl[i];
      dl[j].mid = dp->mp_pgno;
      continue;
    }
    mdbx_dpage_free(env, dp);
  }

done:
  i--;
  txn->mt_dirtyroom += i - j;
  dl[0].mid = j;
  return MDBX_SUCCESS;
}

int mdbx_txn_commit(MDBX_txn *txn) {
  int rc;

  if (unlikely(txn == NULL))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  MDBX_env *env = txn->mt_env;
  if (unlikely(env->me_pid != mdbx_getpid())) {
    env->me_flags |= MDBX_FATAL_ERROR;
    return MDBX_PANIC;
  }

  if (txn->mt_child) {
    rc = mdbx_txn_commit(txn->mt_child);
    txn->mt_child = NULL;
    if (unlikely(rc != MDBX_SUCCESS))
      goto fail;
  }

  /* mdbx_txn_end() mode for a commit which writes nothing */
  unsigned end_mode =
      MDBX_END_EMPTY_COMMIT | MDBX_END_UPDATE | MDBX_END_SLOT | MDBX_END_FREE;
  if (unlikely(F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY)))
    goto done;

  if (unlikely(txn->mt_flags & (MDBX_TXN_FINISHED | MDBX_TXN_ERROR))) {
    mdbx_debug("error flag is set, can't commit");
    if (txn->mt_parent)
      txn->mt_parent->mt_flags |= MDBX_TXN_ERROR;
    rc = MDBX_BAD_TXN;
    goto fail;
  }

  if (txn->mt_parent) {
    MDBX_txn *parent = txn->mt_parent;
    MDBX_page **lp;
    MDBX_ID2L dst, src;
    MDBX_PNL pspill;
    unsigned i, x, y, len, ps_len;

    /* Append our reclaim list to parent's */
    if (txn->mt_lifo_reclaimed) {
      if (parent->mt_lifo_reclaimed) {
        rc = mdbx_txl_append_list(&parent->mt_lifo_reclaimed,
                                  txn->mt_lifo_reclaimed);
        if (unlikely(rc != MDBX_SUCCESS))
          goto fail;
        mdbx_txl_free(txn->mt_lifo_reclaimed);
      } else
        parent->mt_lifo_reclaimed = txn->mt_lifo_reclaimed;
      txn->mt_lifo_reclaimed = NULL;
    }

    /* Append our free list to parent's */
    rc = mdbx_pnl_append_list(&parent->mt_befree_pages, txn->mt_befree_pages);
    if (unlikely(rc != MDBX_SUCCESS))
      goto fail;
    mdbx_pnl_free(txn->mt_befree_pages);
    /* Failures after this must either undo the changes
     * to the parent or set MDBX_TXN_ERROR in the parent. */

    parent->mt_next_pgno = txn->mt_next_pgno;
    parent->mt_end_pgno = txn->mt_end_pgno;
    parent->mt_flags = txn->mt_flags;

    /* Merge our cursors into parent's and close them */
    mdbx_cursors_eot(txn, 1);

    /* Update parent's DB table. */
    memcpy(parent->mt_dbs, txn->mt_dbs, txn->mt_numdbs * sizeof(MDBX_db));
    parent->mt_numdbs = txn->mt_numdbs;
    parent->mt_dbflags[FREE_DBI] = txn->mt_dbflags[FREE_DBI];
    parent->mt_dbflags[MAIN_DBI] = txn->mt_dbflags[MAIN_DBI];
    for (i = CORE_DBS; i < txn->mt_numdbs; i++) {
      /* preserve parent's DB_NEW status */
      parent->mt_dbflags[i] =
          txn->mt_dbflags[i] | (parent->mt_dbflags[i] & DB_NEW);
    }

    dst = parent->mt_rw_dirtylist;
    src = txn->mt_rw_dirtylist;
    /* Remove anything in our dirty list from parent's spill list */
    if ((pspill = parent->mt_spill_pages) && (ps_len = pspill[0])) {
      x = y = ps_len;
      pspill[0] = (pgno_t)-1;
      /* Mark our dirty pages as deleted in parent spill list */
      for (i = 0, len = src[0].mid; ++i <= len;) {
        pgno_t pn = src[i].mid << 1;
        while (pn > pspill[x])
          x--;
        if (pn == pspill[x]) {
          pspill[x] = 1;
          y = --x;
        }
      }
      /* Squash deleted pagenums if we deleted any */
      for (x = y; ++x <= ps_len;)
        if (!(pspill[x] & 1))
          pspill[++y] = pspill[x];
      pspill[0] = y;
    }

    /* Remove anything in our spill list from parent's dirty list */
    if (txn->mt_spill_pages && txn->mt_spill_pages[0]) {
      for (i = 1; i <= txn->mt_spill_pages[0]; i++) {
        pgno_t pn = txn->mt_spill_pages[i];
        if (pn & 1)
          continue; /* deleted spillpg */
        pn >>= 1;
        y = mdbx_mid2l_search(dst, pn);
        if (y <= dst[0].mid && dst[y].mid == pn) {
          free(dst[y].mptr);
          while (y < dst[0].mid) {
            dst[y] = dst[y + 1];
            y++;
          }
          dst[0].mid--;
        }
      }
    }

    /* Find len = length of merging our dirty list with parent's */
    x = dst[0].mid;
    dst[0].mid = 0; /* simplify loops */
    if (parent->mt_parent) {
      len = x + src[0].mid;
      y = mdbx_mid2l_search(src, dst[x].mid + 1) - 1;
      for (i = x; y && i; y--) {
        pgno_t yp = src[y].mid;
        while (yp < dst[i].mid)
          i--;
        if (yp == dst[i].mid) {
          i--;
          len--;
        }
      }
    } else { /* Simplify the above for single-ancestor case */
      len = MDBX_PNL_UM_MAX - txn->mt_dirtyroom;
    }
    /* Merge our dirty list with parent's */
    y = src[0].mid;
    for (i = len; y; dst[i--] = src[y--]) {
      pgno_t yp = src[y].mid;
      while (yp < dst[x].mid)
        dst[i--] = dst[x--];
      if (yp == dst[x].mid)
        free(dst[x--].mptr);
    }
    mdbx_tassert(txn, i == x);
    dst[0].mid = len;
    free(txn->mt_rw_dirtylist);
    parent->mt_dirtyroom = txn->mt_dirtyroom;
    if (txn->mt_spill_pages) {
      if (parent->mt_spill_pages) {
        /* TODO: Prevent failure here, so parent does not fail */
        rc = mdbx_pnl_append_list(&parent->mt_spill_pages, txn->mt_spill_pages);
        if (unlikely(rc != MDBX_SUCCESS))
          parent->mt_flags |= MDBX_TXN_ERROR;
        mdbx_pnl_free(txn->mt_spill_pages);
        mdbx_pnl_sort(parent->mt_spill_pages);
      } else {
        parent->mt_spill_pages = txn->mt_spill_pages;
      }
    }

    /* Append our loose page list to parent's */
    for (lp = &parent->mt_loose_pages; *lp; lp = &NEXT_LOOSE_PAGE(*lp))
      ;
    *lp = txn->mt_loose_pages;
    parent->mt_loose_count += txn->mt_loose_count;

    parent->mt_child = NULL;
    mdbx_pnl_free(((MDBX_ntxn *)txn)->mnt_pgstate.mf_reclaimed_pglist);
    txn->mt_signature = 0;
    free(txn);
    return rc;
  }

  if (unlikely(txn != env->me_txn)) {
    mdbx_debug("attempt to commit unknown transaction");
    rc = MDBX_EINVAL;
    goto fail;
  }

  mdbx_cursors_eot(txn, 0);
  end_mode |= MDBX_END_EOTDONE;

  if (!txn->mt_rw_dirtylist[0].mid &&
      !(txn->mt_flags & (MDBX_TXN_DIRTY | MDBX_TXN_SPILLS)))
    goto done;

  mdbx_debug("committing txn %" PRIaTXN " %p on mdbenv %p, root page %" PRIaPGNO
             "/%" PRIaPGNO,
             txn->mt_txnid, (void *)txn, (void *)env,
             txn->mt_dbs[MAIN_DBI].md_root, txn->mt_dbs[FREE_DBI].md_root);

  /* Update DB root pointers */
  if (txn->mt_numdbs > CORE_DBS) {
    MDBX_cursor mc;
    MDBX_dbi i;
    MDBX_val data;
    data.iov_len = sizeof(MDBX_db);

    mdbx_cursor_init(&mc, txn, MAIN_DBI, NULL);
    for (i = CORE_DBS; i < txn->mt_numdbs; i++) {
      if (txn->mt_dbflags[i] & DB_DIRTY) {
        if (unlikely(TXN_DBI_CHANGED(txn, i))) {
          rc = MDBX_BAD_DBI;
          goto fail;
        }
        data.iov_base = &txn->mt_dbs[i];
        rc = mdbx_cursor_put(&mc, &txn->mt_dbxs[i].md_name, &data, F_SUBDATA);
        if (unlikely(rc != MDBX_SUCCESS))
          goto fail;
      }
    }
  }

  rc = mdbx_freelist_save(txn);
  if (unlikely(rc != MDBX_SUCCESS))
    goto fail;

  mdbx_pnl_free(env->me_reclaimed_pglist);
  env->me_reclaimed_pglist = NULL;
  mdbx_pnl_shrink(&txn->mt_befree_pages);

  if (mdbx_audit_enabled())
    mdbx_audit(txn);

  rc = mdbx_page_flush(txn, 0);
  if (likely(rc == MDBX_SUCCESS)) {
    MDBX_meta meta, *head = mdbx_meta_head(env);

    meta.mm_magic_and_version = head->mm_magic_and_version;
    meta.mm_extra_flags = head->mm_extra_flags;
    meta.mm_validator_id = head->mm_validator_id;
    meta.mm_extra_pagehdr = head->mm_extra_pagehdr;

    meta.mm_geo = head->mm_geo;
    meta.mm_geo.next = txn->mt_next_pgno;
    meta.mm_geo.now = txn->mt_end_pgno;
    meta.mm_dbs[FREE_DBI] = txn->mt_dbs[FREE_DBI];
    meta.mm_dbs[MAIN_DBI] = txn->mt_dbs[MAIN_DBI];
    meta.mm_canary = txn->mt_canary;
    mdbx_meta_set_txnid(env, &meta, txn->mt_txnid);

    rc = mdbx_sync_locked(
        env, env->me_flags | txn->mt_flags | MDBX_SHRINK_ALLOWED, &meta);
  }
  if (unlikely(rc != MDBX_SUCCESS))
    goto fail;
  end_mode = MDBX_END_COMMITTED | MDBX_END_UPDATE | MDBX_END_EOTDONE;

done:
  return mdbx_txn_end(txn, end_mode);

fail:
  mdbx_txn_abort(txn);
  return rc;
}

/* Read the environment parameters of a DB environment
 * before mapping it into memory. */
static int __cold mdbx_read_header(MDBX_env *env, MDBX_meta *meta) {
  assert(offsetof(MDBX_page, mp_meta) == PAGEHDRSZ);
  memset(meta, 0, sizeof(MDBX_meta));
  meta->mm_datasync_sign = MDBX_DATASIGN_WEAK;
  int rc = MDBX_CORRUPTED;

  /* Read twice all meta pages so we can find the latest one. */
  unsigned loop_limit = NUM_METAS * 2;
  for (unsigned loop_count = 0; loop_count < loop_limit; ++loop_count) {
    MDBX_page page;

    /* We don't know the page size on first time.
     * So, just guess it. */
    unsigned guess_pagesize = meta->mm_psize;
    if (guess_pagesize == 0)
      guess_pagesize =
          (loop_count > NUM_METAS) ? env->me_psize : env->me_os_psize;

    const unsigned meta_number = loop_count % NUM_METAS;
    const unsigned offset = guess_pagesize * meta_number;

    unsigned retryleft = 42;
    while (1) {
      int err = mdbx_pread(env->me_fd, &page, sizeof(page), offset);
      if (err != MDBX_SUCCESS) {
        mdbx_error("read meta[%u,%u]: %i, %s", offset, (unsigned)sizeof(page),
                   err, mdbx_strerror(err));
        return err;
      }

      MDBX_page again;
      err = mdbx_pread(env->me_fd, &again, sizeof(again), offset);
      if (err != MDBX_SUCCESS) {
        mdbx_error("read meta[%u,%u]: %i, %s", offset, (unsigned)sizeof(again),
                   err, mdbx_strerror(err));
        return err;
      }

      if (memcmp(&page, &again, sizeof(page)) == 0 || --retryleft == 0)
        break;

      mdbx_info("meta[%u] was updated, re-read it", meta_number);
    }

    if (!retryleft) {
      mdbx_error("meta[%u] is too volatile, skip it", meta_number);
      continue;
    }

    if (page.mp_pgno != meta_number) {
      mdbx_error("meta[%u] has invalid pageno %" PRIaPGNO, meta_number,
                 page.mp_pgno);
      return MDBX_INVALID;
    }

    if (!F_ISSET(page.mp_flags, P_META)) {
      mdbx_error("page #%u not a meta-page", meta_number);
      return MDBX_INVALID;
    }

    if (page.mp_meta.mm_magic_and_version != MDBX_DATA_MAGIC) {
      mdbx_error("meta[%u] has invalid magic/version", meta_number);
      return ((page.mp_meta.mm_magic_and_version >> 8) != MDBX_MAGIC)
                 ? MDBX_INVALID
                 : MDBX_VERSION_MISMATCH;
    }

    if (page.mp_meta.mm_txnid_a != page.mp_meta.mm_txnid_b) {
      mdbx_warning("meta[%u] not completely updated, skip it", meta_number);
      continue;
    }

    /* LY: check signature as a checksum */
    if (META_IS_STEADY(&page.mp_meta) &&
        page.mp_meta.mm_datasync_sign != mdbx_meta_sign(&page.mp_meta)) {
      mdbx_notice("meta[%u] has invalid steady-checksum (0x%" PRIx64
                  " != 0x%" PRIx64 "), skip it",
                  meta_number, page.mp_meta.mm_datasync_sign,
                  mdbx_meta_sign(&page.mp_meta));
      continue;
    }

    /* LY: check pagesize */
    if (!mdbx_is_power2(page.mp_meta.mm_psize) ||
        page.mp_meta.mm_psize < MIN_PAGESIZE ||
        page.mp_meta.mm_psize > MAX_PAGESIZE) {
      mdbx_notice("meta[%u] has invalid pagesize (%u), skip it", meta_number,
                  page.mp_meta.mm_psize);
      rc = MDBX_VERSION_MISMATCH;
      continue;
    }

    mdbx_debug("read meta%" PRIaPGNO " = root %" PRIaPGNO "/%" PRIaPGNO
               ", geo %" PRIaPGNO "/%" PRIaPGNO "-%" PRIaPGNO "/%" PRIaPGNO
               " +%u -%u, txn_id %" PRIaTXN ", %s",
               page.mp_pgno, page.mp_meta.mm_dbs[MAIN_DBI].md_root,
               page.mp_meta.mm_dbs[FREE_DBI].md_root, page.mp_meta.mm_geo.lower,
               page.mp_meta.mm_geo.next, page.mp_meta.mm_geo.now,
               page.mp_meta.mm_geo.upper, page.mp_meta.mm_geo.grow,
               page.mp_meta.mm_geo.shrink, page.mp_meta.mm_txnid_a,
               mdbx_durable_str(&page.mp_meta));

    /* LY: check min-pages value */
    if (page.mp_meta.mm_geo.lower < MIN_PAGENO ||
        page.mp_meta.mm_geo.lower > MAX_PAGENO) {
      mdbx_notice("meta[%u] has invalid min-pages (%" PRIaPGNO "), skip it",
                  meta_number, page.mp_meta.mm_geo.lower);
      rc = MDBX_INVALID;
      continue;
    }

    /* LY: check max-pages value */
    if (page.mp_meta.mm_geo.upper < MIN_PAGENO ||
        page.mp_meta.mm_geo.upper > MAX_PAGENO ||
        page.mp_meta.mm_geo.upper < page.mp_meta.mm_geo.lower) {
      mdbx_notice("meta[%u] has invalid max-pages (%" PRIaPGNO "), skip it",
                  meta_number, page.mp_meta.mm_geo.upper);
      rc = MDBX_INVALID;
      continue;
    }

    /* LY: check mapsize limits */
    const uint64_t mapsize_min =
        page.mp_meta.mm_geo.lower * (uint64_t)page.mp_meta.mm_psize;
    const uint64_t mapsize_max =
        page.mp_meta.mm_geo.upper * (uint64_t)page.mp_meta.mm_psize;
    STATIC_ASSERT(MAX_MAPSIZE < SSIZE_MAX - MAX_PAGESIZE);
    STATIC_ASSERT(MIN_MAPSIZE < MAX_MAPSIZE);
    if (mapsize_min < MIN_MAPSIZE || mapsize_max > MAX_MAPSIZE) {
      mdbx_notice("meta[%u] has invalid min-mapsize (%" PRIu64 "), skip it",
                  meta_number, mapsize_min);
      rc = MDBX_VERSION_MISMATCH;
      continue;
    }

    STATIC_ASSERT(MIN_MAPSIZE < MAX_MAPSIZE);
    if (mapsize_max > MAX_MAPSIZE ||
        MAX_PAGENO < mdbx_roundup2((size_t)mapsize_max, env->me_os_psize) /
                         (uint64_t)page.mp_meta.mm_psize) {
      mdbx_notice("meta[%u] has too large max-mapsize (%" PRIu64 "), skip it",
                  meta_number, mapsize_max);
      rc = MDBX_TOO_LARGE;
      continue;
    }

    /* LY: check end_pgno */
    if (page.mp_meta.mm_geo.now < page.mp_meta.mm_geo.lower ||
        page.mp_meta.mm_geo.now > page.mp_meta.mm_geo.upper) {
      mdbx_notice("meta[%u] has invalid end-pageno (%" PRIaPGNO "), skip it",
                  meta_number, page.mp_meta.mm_geo.now);
      rc = MDBX_CORRUPTED;
      continue;
    }

    /* LY: check last_pgno */
    if (page.mp_meta.mm_geo.next < MIN_PAGENO ||
        page.mp_meta.mm_geo.next - 1 > MAX_PAGENO) {
      mdbx_notice("meta[%u] has invalid next-pageno (%" PRIaPGNO "), skip it",
                  meta_number, page.mp_meta.mm_geo.next);
      rc = MDBX_CORRUPTED;
      continue;
    }

    if (page.mp_meta.mm_geo.next > page.mp_meta.mm_geo.now) {
      mdbx_notice("meta[%u] next-pageno (%" PRIaPGNO
                  ") is beyond end-pgno (%" PRIaPGNO "), skip it",
                  meta_number, page.mp_meta.mm_geo.next,
                  page.mp_meta.mm_geo.now);
      rc = MDBX_CORRUPTED;
      continue;
    }

    /* LY: FreeDB root */
    if (page.mp_meta.mm_dbs[FREE_DBI].md_root == P_INVALID) {
      if (page.mp_meta.mm_dbs[FREE_DBI].md_branch_pages ||
          page.mp_meta.mm_dbs[FREE_DBI].md_depth ||
          page.mp_meta.mm_dbs[FREE_DBI].md_entries ||
          page.mp_meta.mm_dbs[FREE_DBI].md_leaf_pages ||
          page.mp_meta.mm_dbs[FREE_DBI].md_overflow_pages) {
        mdbx_notice("meta[%u] has false-empty freedb, skip it", meta_number);
        rc = MDBX_CORRUPTED;
        continue;
      }
    } else if (page.mp_meta.mm_dbs[FREE_DBI].md_root >=
               page.mp_meta.mm_geo.next) {
      mdbx_notice("meta[%u] has invalid freedb-root %" PRIaPGNO ", skip it",
                  meta_number, page.mp_meta.mm_dbs[FREE_DBI].md_root);
      rc = MDBX_CORRUPTED;
      continue;
    }

    /* LY: MainDB root */
    if (page.mp_meta.mm_dbs[MAIN_DBI].md_root == P_INVALID) {
      if (page.mp_meta.mm_dbs[MAIN_DBI].md_branch_pages ||
          page.mp_meta.mm_dbs[MAIN_DBI].md_depth ||
          page.mp_meta.mm_dbs[MAIN_DBI].md_entries ||
          page.mp_meta.mm_dbs[MAIN_DBI].md_leaf_pages ||
          page.mp_meta.mm_dbs[MAIN_DBI].md_overflow_pages) {
        mdbx_notice("meta[%u] has false-empty maindb", meta_number);
        rc = MDBX_CORRUPTED;
        continue;
      }
    } else if (page.mp_meta.mm_dbs[MAIN_DBI].md_root >=
               page.mp_meta.mm_geo.next) {
      mdbx_notice("meta[%u] has invalid maindb-root %" PRIaPGNO ", skip it",
                  meta_number, page.mp_meta.mm_dbs[MAIN_DBI].md_root);
      rc = MDBX_CORRUPTED;
      continue;
    }

    if (page.mp_meta.mm_txnid_a == 0) {
      mdbx_warning("meta[%u] has zero txnid, skip it", meta_number);
      continue;
    }

    if (mdbx_meta_ot(prefer_steady, env, meta, &page.mp_meta)) {
      *meta = page.mp_meta;
      if (META_IS_WEAK(meta))
        loop_limit += 1; /* LY: should re-read to hush race with update */
      mdbx_info("latch meta[%u]", meta_number);
    }
  }

  if (META_IS_WEAK(meta)) {
    mdbx_error("no usable meta-pages, database is corrupted");
    return rc;
  }

  return MDBX_SUCCESS;
}

static MDBX_page *__cold mdbx_meta_model(const MDBX_env *env, MDBX_page *model,
                                         unsigned num) {

  mdbx_ensure(env, mdbx_is_power2(env->me_psize));
  mdbx_ensure(env, env->me_psize >= MIN_PAGESIZE);
  mdbx_ensure(env, env->me_psize <= MAX_PAGESIZE);
  mdbx_ensure(env, env->me_dbgeo.lower >= MIN_MAPSIZE);
  mdbx_ensure(env, env->me_dbgeo.upper <= MAX_MAPSIZE);
  mdbx_ensure(env, env->me_dbgeo.now >= env->me_dbgeo.lower);
  mdbx_ensure(env, env->me_dbgeo.now <= env->me_dbgeo.upper);

  memset(model, 0, sizeof(*model));
  model->mp_pgno = num;
  model->mp_flags = P_META;
  model->mp_meta.mm_magic_and_version = MDBX_DATA_MAGIC;

  model->mp_meta.mm_geo.lower = bytes2pgno(env, env->me_dbgeo.lower);
  model->mp_meta.mm_geo.upper = bytes2pgno(env, env->me_dbgeo.upper);
  model->mp_meta.mm_geo.grow = (uint16_t)bytes2pgno(env, env->me_dbgeo.grow);
  model->mp_meta.mm_geo.shrink =
      (uint16_t)bytes2pgno(env, env->me_dbgeo.shrink);
  model->mp_meta.mm_geo.now = bytes2pgno(env, env->me_dbgeo.now);
  model->mp_meta.mm_geo.next = NUM_METAS;

  mdbx_ensure(env, model->mp_meta.mm_geo.lower >= MIN_PAGENO);
  mdbx_ensure(env, model->mp_meta.mm_geo.upper <= MAX_PAGENO);
  mdbx_ensure(env, model->mp_meta.mm_geo.now >= model->mp_meta.mm_geo.lower);
  mdbx_ensure(env, model->mp_meta.mm_geo.now <= model->mp_meta.mm_geo.upper);
  mdbx_ensure(env, model->mp_meta.mm_geo.next >= MIN_PAGENO);
  mdbx_ensure(env, model->mp_meta.mm_geo.next <= model->mp_meta.mm_geo.now);
  mdbx_ensure(env, model->mp_meta.mm_geo.grow ==
                       bytes2pgno(env, env->me_dbgeo.grow));
  mdbx_ensure(env, model->mp_meta.mm_geo.shrink ==
                       bytes2pgno(env, env->me_dbgeo.shrink));

  model->mp_meta.mm_psize = env->me_psize;
  model->mp_meta.mm_flags = (uint16_t)env->me_flags;
  model->mp_meta.mm_flags |=
      MDBX_INTEGERKEY; /* this is mm_dbs[FREE_DBI].md_flags */
  model->mp_meta.mm_dbs[FREE_DBI].md_root = P_INVALID;
  model->mp_meta.mm_dbs[MAIN_DBI].md_root = P_INVALID;
  mdbx_meta_set_txnid(env, &model->mp_meta, MIN_TXNID + num);
  model->mp_meta.mm_datasync_sign = mdbx_meta_sign(&model->mp_meta);
  return (MDBX_page *)((uint8_t *)model + env->me_psize);
}

/* Fill in most of the zeroed meta-pages for an empty database environment.
 * Return pointer to recenly (head) meta-page. */
static MDBX_page *__cold mdbx_init_metas(const MDBX_env *env, void *buffer) {
  MDBX_page *page0 = (MDBX_page *)buffer;
  MDBX_page *page1 = mdbx_meta_model(env, page0, 0);
  MDBX_page *page2 = mdbx_meta_model(env, page1, 1);
  mdbx_meta_model(env, page2, 2);
  page2->mp_meta.mm_datasync_sign = MDBX_DATASIGN_WEAK;
  mdbx_assert(env, !mdbx_meta_eq(env, &page0->mp_meta, &page1->mp_meta));
  mdbx_assert(env, !mdbx_meta_eq(env, &page1->mp_meta, &page2->mp_meta));
  mdbx_assert(env, !mdbx_meta_eq(env, &page2->mp_meta, &page0->mp_meta));
  return page1;
}

static int mdbx_sync_locked(MDBX_env *env, unsigned flags,
                            MDBX_meta *const pending) {
  mdbx_assert(env, ((env->me_flags ^ flags) & MDBX_WRITEMAP) == 0);
  MDBX_meta *const meta0 = METAPAGE(env, 0);
  MDBX_meta *const meta1 = METAPAGE(env, 1);
  MDBX_meta *const meta2 = METAPAGE(env, 2);
  MDBX_meta *const head = mdbx_meta_head(env);

  mdbx_assert(env, mdbx_meta_eq_mask(env) == 0);
  mdbx_assert(env,
              pending < METAPAGE(env, 0) || pending > METAPAGE(env, NUM_METAS));
  mdbx_assert(env, (env->me_flags & (MDBX_RDONLY | MDBX_FATAL_ERROR)) == 0);
  mdbx_assert(env, !META_IS_STEADY(head) || env->me_sync_pending != 0);
  mdbx_assert(env, pending->mm_geo.next <= pending->mm_geo.now);

  const size_t usedbytes = pgno_align2os_bytes(env, pending->mm_geo.next);
  if (env->me_sync_threshold && env->me_sync_pending >= env->me_sync_threshold)
    flags &= MDBX_WRITEMAP | MDBX_SHRINK_ALLOWED;

  /* LY: step#1 - sync previously written/updated data-pages */
  int rc = MDBX_RESULT_TRUE;
  if (env->me_sync_pending && (flags & MDBX_NOSYNC) == 0) {
    mdbx_assert(env, ((flags ^ env->me_flags) & MDBX_WRITEMAP) == 0);
    MDBX_meta *const steady = mdbx_meta_steady(env);
    if (flags & MDBX_WRITEMAP) {
      rc = mdbx_msync(&env->me_dxb_mmap, 0, usedbytes, flags & MDBX_MAPASYNC);
      if (unlikely(rc != MDBX_SUCCESS))
        goto fail;
      if ((flags & MDBX_MAPASYNC) == 0) {
        if (unlikely(pending->mm_geo.next > steady->mm_geo.now)) {
          rc = mdbx_filesize_sync(env->me_fd);
          if (unlikely(rc != MDBX_SUCCESS))
            goto fail;
        }
        env->me_sync_pending = 0;
      }
    } else {
      rc = mdbx_filesync(env->me_fd, pending->mm_geo.next > steady->mm_geo.now);
      if (unlikely(rc != MDBX_SUCCESS))
        goto fail;
      env->me_sync_pending = 0;
    }
  }

#if defined(_WIN32) || defined(_WIN64)
/* Windows is unable shrinking a mapped file */
#else
  /* LY: check conditions to shrink datafile */
  pgno_t shrink = 0;
  if ((flags & MDBX_SHRINK_ALLOWED) && pending->mm_geo.shrink &&
      pending->mm_geo.now - pending->mm_geo.next > pending->mm_geo.shrink) {
    const pgno_t aligner =
        pending->mm_geo.grow ? pending->mm_geo.grow : pending->mm_geo.shrink;
    const pgno_t aligned = pgno_align2os_pgno(
        env, pending->mm_geo.next + aligner - pending->mm_geo.next % aligner);
    if (pending->mm_geo.now > aligned) {
      shrink = pending->mm_geo.now - aligned;
      pending->mm_geo.now = aligned;
      if (mdbx_meta_txnid_stable(env, head) == pending->mm_txnid_a)
        mdbx_meta_set_txnid(env, pending, pending->mm_txnid_a + 1);
    }
  }
#endif /* not a Windows */

  /* Steady or Weak */
  if (env->me_sync_pending == 0) {
    pending->mm_datasync_sign = mdbx_meta_sign(pending);
  } else {
    pending->mm_datasync_sign =
        (flags & MDBX_UTTERLY_NOSYNC) == MDBX_UTTERLY_NOSYNC
            ? MDBX_DATASIGN_NONE
            : MDBX_DATASIGN_WEAK;
  }

  MDBX_meta *target = nullptr;
  if (mdbx_meta_txnid_stable(env, head) == pending->mm_txnid_a) {
    mdbx_assert(env, memcmp(&head->mm_dbs, &pending->mm_dbs,
                            sizeof(head->mm_dbs)) == 0);
    mdbx_assert(env, memcmp(&head->mm_canary, &pending->mm_canary,
                            sizeof(head->mm_canary)) == 0);
    mdbx_assert(env, memcmp(&head->mm_geo, &pending->mm_geo,
                            sizeof(pending->mm_geo)) == 0);
    if (!META_IS_STEADY(head) && META_IS_STEADY(pending))
      target = head;
    else {
      mdbx_ensure(env, mdbx_meta_eq(env, head, pending));
      mdbx_debug("skip update meta");
      return MDBX_SUCCESS;
    }
  } else if (head == meta0)
    target = mdbx_meta_ancient(prefer_steady, env, meta1, meta2);
  else if (head == meta1)
    target = mdbx_meta_ancient(prefer_steady, env, meta0, meta2);
  else {
    mdbx_assert(env, head == meta2);
    target = mdbx_meta_ancient(prefer_steady, env, meta0, meta1);
  }

  /* LY: step#2 - update meta-page. */
  mdbx_debug("writing meta%" PRIaPGNO " = root %" PRIaPGNO "/%" PRIaPGNO
             ", geo %" PRIaPGNO "/%" PRIaPGNO "-%" PRIaPGNO "/%" PRIaPGNO
             " +%u -%u, txn_id %" PRIaTXN ", %s",
             container_of(target, MDBX_page, mp_data)->mp_pgno,
             pending->mm_dbs[MAIN_DBI].md_root,
             pending->mm_dbs[FREE_DBI].md_root, pending->mm_geo.lower,
             pending->mm_geo.next, pending->mm_geo.now, pending->mm_geo.upper,
             pending->mm_geo.grow, pending->mm_geo.shrink, pending->mm_txnid_a,
             mdbx_durable_str(pending));

  mdbx_debug("meta0: %s, %s, txn_id %" PRIaTXN ", root %" PRIaPGNO
             "/%" PRIaPGNO,
             (meta0 == head) ? "head" : (meta0 == target) ? "tail" : "stay",
             mdbx_durable_str(meta0), mdbx_meta_txnid_fluid(env, meta0),
             meta0->mm_dbs[MAIN_DBI].md_root, meta0->mm_dbs[FREE_DBI].md_root);
  mdbx_debug("meta1: %s, %s, txn_id %" PRIaTXN ", root %" PRIaPGNO
             "/%" PRIaPGNO,
             (meta1 == head) ? "head" : (meta1 == target) ? "tail" : "stay",
             mdbx_durable_str(meta1), mdbx_meta_txnid_fluid(env, meta1),
             meta1->mm_dbs[MAIN_DBI].md_root, meta1->mm_dbs[FREE_DBI].md_root);
  mdbx_debug("meta2: %s, %s, txn_id %" PRIaTXN ", root %" PRIaPGNO
             "/%" PRIaPGNO,
             (meta2 == head) ? "head" : (meta2 == target) ? "tail" : "stay",
             mdbx_durable_str(meta2), mdbx_meta_txnid_fluid(env, meta2),
             meta2->mm_dbs[MAIN_DBI].md_root, meta2->mm_dbs[FREE_DBI].md_root);

  mdbx_assert(env, !mdbx_meta_eq(env, pending, meta0));
  mdbx_assert(env, !mdbx_meta_eq(env, pending, meta1));
  mdbx_assert(env, !mdbx_meta_eq(env, pending, meta2));

  mdbx_assert(env, ((env->me_flags ^ flags) & MDBX_WRITEMAP) == 0);
  mdbx_ensure(env,
              target == head ||
                  mdbx_meta_txnid_stable(env, target) < pending->mm_txnid_a);
  if (env->me_flags & MDBX_WRITEMAP) {
    mdbx_jitter4testing(true);
    if (likely(target != head)) {
      /* LY: 'invalidate' the meta. */
      target->mm_datasync_sign = MDBX_DATASIGN_WEAK;
      mdbx_meta_update_begin(env, target, pending->mm_txnid_a);
#ifndef NDEBUG
      /* debug: provoke failure to catch a violators */
      memset(target->mm_dbs, 0xCC,
             sizeof(target->mm_dbs) + sizeof(target->mm_canary));
      mdbx_jitter4testing(false);
#endif

      /* LY: update info */
      target->mm_geo = pending->mm_geo;
      target->mm_dbs[FREE_DBI] = pending->mm_dbs[FREE_DBI];
      target->mm_dbs[MAIN_DBI] = pending->mm_dbs[MAIN_DBI];
      target->mm_canary = pending->mm_canary;
      mdbx_jitter4testing(true);
      mdbx_coherent_barrier();

      /* LY: 'commit' the meta */
      mdbx_meta_update_end(env, target, pending->mm_txnid_b);
      mdbx_jitter4testing(true);
    } else {
      /* dangerous case (target == head), only mm_datasync_sign could
       * me updated, check assertions once again */
      mdbx_ensure(env,
                  mdbx_meta_txnid_stable(env, head) == pending->mm_txnid_a &&
                      !META_IS_STEADY(head) && META_IS_STEADY(pending));
      mdbx_ensure(env, memcmp(&head->mm_geo, &pending->mm_geo,
                              sizeof(head->mm_geo)) == 0);
      mdbx_ensure(env, memcmp(&head->mm_dbs, &pending->mm_dbs,
                              sizeof(head->mm_dbs)) == 0);
      mdbx_ensure(env, memcmp(&head->mm_canary, &pending->mm_canary,
                              sizeof(head->mm_canary)) == 0);
    }
    target->mm_datasync_sign = pending->mm_datasync_sign;
    mdbx_coherent_barrier();
    mdbx_jitter4testing(true);
  } else {
    rc = mdbx_pwrite(env->me_fd, pending, sizeof(MDBX_meta),
                     (uint8_t *)target - env->me_map);
    if (unlikely(rc != MDBX_SUCCESS)) {
    undo:
      mdbx_debug("write failed, disk error?");
      /* On a failure, the pagecache still contains the new data.
       * Try write some old data back, to prevent it from being used. */
      mdbx_pwrite(env->me_fd, (void *)target, sizeof(MDBX_meta),
                  (uint8_t *)target - env->me_map);
      goto fail;
    }
    mdbx_invalidate_cache(target, sizeof(MDBX_meta));
  }

  /* LY: step#3 - sync meta-pages. */
  mdbx_assert(env, ((env->me_flags ^ flags) & MDBX_WRITEMAP) == 0);
  if ((flags & (MDBX_NOSYNC | MDBX_NOMETASYNC)) == 0) {
    mdbx_assert(env, ((flags ^ env->me_flags) & MDBX_WRITEMAP) == 0);
    if (flags & MDBX_WRITEMAP) {
      const size_t offset = (uint8_t *)container_of(head, MDBX_page, mp_meta) -
                            env->me_dxb_mmap.dxb;
      const size_t paged_offset = offset & ~(env->me_os_psize - 1);
      const size_t paged_length = mdbx_roundup2(
          env->me_psize + offset - paged_offset, env->me_os_psize);
      rc = mdbx_msync(&env->me_dxb_mmap, paged_offset, paged_length,
                      flags & MDBX_MAPASYNC);
      if (unlikely(rc != MDBX_SUCCESS))
        goto fail;
    } else {
      rc = mdbx_filesync(env->me_fd, false);
      if (rc != MDBX_SUCCESS)
        goto undo;
    }
  }

#if defined(_WIN32) || defined(_WIN64)
/* Windows is unable shrinking a mapped file */
#else
  /* LY: shrink datafile if needed */
  if (unlikely(shrink)) {
    mdbx_info("shrink to %" PRIaPGNO " pages (-%" PRIaPGNO ")",
              pending->mm_geo.now, shrink);
    rc = mdbx_mapresize(env, pending->mm_geo.now, pending->mm_geo.upper);
    if (MDBX_IS_ERROR(rc))
      goto fail;
  }
#endif /* not a Windows */

  return MDBX_SUCCESS;

fail:
  env->me_flags |= MDBX_FATAL_ERROR;
  return rc;
}

int __cold mdbx_env_get_maxkeysize(MDBX_env *env) {
  if (!env || env->me_signature != MDBX_ME_SIGNATURE || !env->me_maxkey_limit)
    return -MDBX_EINVAL;
  return env->me_maxkey_limit;
}

#define mdbx_nodemax(pagesize)                                                 \
  (((((pagesize)-PAGEHDRSZ) / MDBX_MINKEYS) & -(intptr_t)2) - sizeof(indx_t))

#define mdbx_maxkey(nodemax) ((nodemax) - (NODESIZE + sizeof(MDBX_db)))

#define mdbx_maxfree1pg(pagesize) (((pagesize)-PAGEHDRSZ) / sizeof(pgno_t) - 1)

int mdbx_get_maxkeysize(size_t pagesize) {
  if (pagesize == 0)
    pagesize = mdbx_syspagesize();

  intptr_t nodemax = mdbx_nodemax(pagesize);
  if (nodemax < 0)
    return -MDBX_EINVAL;

  intptr_t maxkey = mdbx_maxkey(nodemax);
  return (maxkey > 0 && maxkey < INT_MAX) ? (int)maxkey : -MDBX_EINVAL;
}

static void __cold mdbx_setup_pagesize(MDBX_env *env, const size_t pagesize) {
  STATIC_ASSERT(SSIZE_MAX > MAX_MAPSIZE);
  STATIC_ASSERT(MIN_PAGESIZE > sizeof(MDBX_page));
  mdbx_ensure(env, mdbx_is_power2(pagesize));
  mdbx_ensure(env, pagesize >= MIN_PAGESIZE);
  mdbx_ensure(env, pagesize <= MAX_PAGESIZE);
  env->me_psize = (unsigned)pagesize;

  STATIC_ASSERT(mdbx_maxfree1pg(MIN_PAGESIZE) > 42);
  STATIC_ASSERT(mdbx_maxfree1pg(MAX_PAGESIZE) < MDBX_PNL_DB_MAX);
  const intptr_t maxfree_1pg = (pagesize - PAGEHDRSZ) / sizeof(pgno_t) - 1;
  mdbx_ensure(env, maxfree_1pg > 42 && maxfree_1pg < MDBX_PNL_DB_MAX);
  env->me_maxfree_1pg = (unsigned)maxfree_1pg;

  STATIC_ASSERT(mdbx_nodemax(MIN_PAGESIZE) > 42);
  STATIC_ASSERT(mdbx_nodemax(MAX_PAGESIZE) < UINT16_MAX);
  const intptr_t nodemax = mdbx_nodemax(pagesize);
  mdbx_ensure(env, nodemax > 42 && nodemax < UINT16_MAX);
  env->me_nodemax = (unsigned)nodemax;

  STATIC_ASSERT(mdbx_maxkey(MIN_PAGESIZE) > 42);
  STATIC_ASSERT(mdbx_maxkey(MIN_PAGESIZE) < MIN_PAGESIZE);
  STATIC_ASSERT(mdbx_maxkey(MAX_PAGESIZE) > 42);
  STATIC_ASSERT(mdbx_maxkey(MAX_PAGESIZE) < MAX_PAGESIZE);
  const intptr_t maxkey_limit = mdbx_maxkey(env->me_nodemax);
  mdbx_ensure(env, maxkey_limit > 42 && (size_t)maxkey_limit < pagesize);
  env->me_maxkey_limit = (unsigned)maxkey_limit;

  env->me_psize2log = mdbx_log2(pagesize);
  mdbx_assert(env, pgno2bytes(env, 1) == pagesize);
  mdbx_assert(env, bytes2pgno(env, pagesize + pagesize) == 2);
}

int __cold mdbx_env_create(MDBX_env **penv) {
  MDBX_env *env = calloc(1, sizeof(MDBX_env));
  if (!env)
    return MDBX_ENOMEM;

  env->me_maxreaders = DEFAULT_READERS;
  env->me_maxdbs = env->me_numdbs = CORE_DBS;
  env->me_fd = INVALID_HANDLE_VALUE;
  env->me_lfd = INVALID_HANDLE_VALUE;
  env->me_pid = mdbx_getpid();

  int rc;
  const size_t os_psize = mdbx_syspagesize();
  if (!mdbx_is_power2(os_psize) || os_psize < MIN_PAGESIZE) {
    mdbx_error("unsuitable system pagesize %" PRIuPTR, os_psize);
    rc = MDBX_INCOMPATIBLE;
    goto bailout;
  }
  env->me_os_psize = (unsigned)os_psize;
  mdbx_setup_pagesize(env, env->me_os_psize);

  rc = mdbx_fastmutex_init(&env->me_dbi_lock);
  if (unlikely(rc != MDBX_SUCCESS))
    goto bailout;

  VALGRIND_CREATE_MEMPOOL(env, 0, 0);
  env->me_signature = MDBX_ME_SIGNATURE;
  *penv = env;
  return MDBX_SUCCESS;

bailout:
  free(env);
  *penv = nullptr;
  return rc;
}

static int __cold mdbx_env_map(MDBX_env *env, size_t usedsize) {
  int rc = mdbx_mmap(env->me_flags, &env->me_dxb_mmap, env->me_dbgeo.now,
                     env->me_dbgeo.upper);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;

#ifdef MADV_DONTFORK
  if (madvise(env->me_map, env->me_mapsize, MADV_DONTFORK))
    return errno;
#endif

#ifdef MADV_NOHUGEPAGE
  (void)madvise(env->me_map, env->me_mapsize, MADV_NOHUGEPAGE);
#endif

#if defined(MADV_DODUMP) && defined(MADV_DONTDUMP)
  const size_t meta_length = pgno2bytes(env, NUM_METAS);
  (void)madvise(env->me_map, meta_length, MADV_DODUMP);
  if (!(env->me_flags & MDBX_PAGEPERTURB))
    (void)madvise(env->me_map + meta_length, env->me_mapsize - meta_length,
                  MADV_DONTDUMP);
#endif

#ifdef MADV_REMOVE
  if (usedsize && (env->me_flags & MDBX_WRITEMAP)) {
    (void)madvise(env->me_map + usedsize, env->me_mapsize - usedsize,
                  MADV_REMOVE);
  }
#else
  (void)usedsize;
#endif

#if defined(MADV_RANDOM) && defined(MADV_WILLNEED)
  /* Turn on/off readahead. It's harmful when the DB is larger than RAM. */
  if (madvise(env->me_map, env->me_mapsize,
              (env->me_flags & MDBX_NORDAHEAD) ? MADV_RANDOM : MADV_WILLNEED))
    return errno;
#endif

#ifdef USE_VALGRIND
  env->me_valgrind_handle =
      VALGRIND_CREATE_BLOCK(env->me_map, env->me_mapsize, "mdbx");
#endif

  return MDBX_SUCCESS;
}

LIBMDBX_API int mdbx_env_set_geometry(MDBX_env *env, intptr_t size_lower,
                                      intptr_t size_now, intptr_t size_upper,
                                      intptr_t growth_step,
                                      intptr_t shrink_threshold,
                                      intptr_t pagesize) {
  if (unlikely(!env))
    return MDBX_EINVAL;

  if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
    return MDBX_EBADSIGN;

  const bool outside_txn =
      (!env->me_txn0 || env->me_txn0->mt_owner != mdbx_thread_self());

  int rc = MDBX_PROBLEM;
  if (env->me_map) {
    /* env already mapped */
    if (!env->me_lck || (env->me_flags & MDBX_RDONLY))
      return MDBX_EACCESS;

    if (outside_txn) {
      int err = mdbx_txn_lock(env);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
    }
    MDBX_meta *head = mdbx_meta_head(env);

    if (pagesize < 0)
      pagesize = env->me_psize;
    if (pagesize != (intptr_t)env->me_psize) {
      rc = MDBX_EINVAL;
      goto bailout;
    }

    if (size_lower < 0)
      size_lower = pgno2bytes(env, head->mm_geo.lower);
    if (size_now < 0)
      size_now = pgno2bytes(env, head->mm_geo.now);
    if (size_upper < 0)
      size_upper = pgno2bytes(env, head->mm_geo.upper);
    if (growth_step < 0)
      growth_step = pgno2bytes(env, head->mm_geo.grow);
    if (shrink_threshold < 0)
      shrink_threshold = pgno2bytes(env, head->mm_geo.shrink);

    const size_t usedbytes = pgno2bytes(env, head->mm_geo.next);
    if ((size_t)size_upper < usedbytes) {
      rc = MDBX_MAP_FULL;
      goto bailout;
    }
    if ((size_t)size_now < usedbytes)
      size_now = usedbytes;
#if defined(_WIN32) || defined(_WIN64)
    if ((size_t)size_now < env->me_dbgeo.now ||
        (size_t)size_upper < env->me_dbgeo.upper) {
      /* Windows is unable shrinking a mapped file */
      return ERROR_USER_MAPPED_FILE;
    }
#endif /* Windows */
  } else {
    /* env NOT yet mapped */
    if (!outside_txn) {
      rc = MDBX_PANIC;
      goto bailout;
    }

    if (pagesize < 0) {
      pagesize = env->me_os_psize;
      if (pagesize > MAX_PAGESIZE)
        pagesize = MAX_PAGESIZE;
      mdbx_assert(env, pagesize >= MIN_PAGESIZE);
    }
  }

  if (pagesize < MIN_PAGESIZE || pagesize > MAX_PAGESIZE ||
      !mdbx_is_power2(pagesize)) {
    rc = MDBX_EINVAL;
    goto bailout;
  }

  if (size_lower < 0) {
    size_lower = MIN_MAPSIZE;
    if (MIN_MAPSIZE / pagesize < MIN_PAGENO)
      size_lower = MIN_PAGENO * pagesize;
  }

  if (size_now < 0) {
    size_now = DEFAULT_MAPSIZE;
    if (size_now < size_lower)
      size_now = size_lower;
  }

  if (size_upper < 0) {
    if ((size_t)size_now >= MAX_MAPSIZE / 2)
      size_upper = MAX_MAPSIZE;
    else if (MAX_MAPSIZE != MAX_MAPSIZE32 &&
             (size_t)size_now >= MAX_MAPSIZE32 / 2)
      size_upper = MAX_MAPSIZE32;
    else {
      size_upper = size_now + size_now;
      if ((size_t)size_upper < DEFAULT_MAPSIZE * 2)
        size_upper = DEFAULT_MAPSIZE * 2;
    }
    if ((size_t)size_upper / pagesize > MAX_PAGENO)
      size_upper = pagesize * MAX_PAGENO;
  }

  if (unlikely(size_lower < MIN_MAPSIZE || size_lower > size_upper)) {
    rc = MDBX_EINVAL;
    goto bailout;
  }

  if ((uint64_t)size_lower / pagesize < MIN_PAGENO) {
    rc = MDBX_EINVAL;
    goto bailout;
  }

  if (unlikely((size_t)size_upper > MAX_MAPSIZE ||
               (uint64_t)size_upper / pagesize > MAX_PAGENO)) {
    rc = MDBX_TOO_LARGE;
    goto bailout;
  }

  size_lower = mdbx_roundup2(size_lower, env->me_os_psize);
  size_upper = mdbx_roundup2(size_upper, env->me_os_psize);
  size_now = mdbx_roundup2(size_now, env->me_os_psize);

  /* LY: подбираем значение size_upper:
   *  - кратное размеру системной страницы
   *  - без нарушения MAX_MAPSIZE или MAX_PAGENO */
  while (unlikely((size_t)size_upper > MAX_MAPSIZE ||
                  (uint64_t)size_upper / pagesize > MAX_PAGENO)) {
    if ((size_t)size_upper < env->me_os_psize + MIN_MAPSIZE ||
        (size_t)size_upper < env->me_os_psize * (MIN_PAGENO + 1)) {
      /* паранойа на случай переполнения при невероятных значениях */
      rc = MDBX_EINVAL;
      goto bailout;
    }
    size_upper -= env->me_os_psize;
    if ((size_t)size_upper > (size_t)size_lower)
      size_lower = size_upper;
  }
  mdbx_assert(env, (size_upper - size_lower) % env->me_os_psize == 0);

  if (size_now < size_lower)
    size_now = size_lower;
  if (size_now > size_upper)
    size_now = size_upper;

  if (growth_step < 0) {
    growth_step = ((size_t)(size_upper - size_lower)) / 42;
    if (growth_step > size_lower)
      growth_step = size_lower;
    if (growth_step < 65536)
      growth_step = 65536;
    if ((size_t)growth_step > MEGABYTE * 16)
      growth_step = MEGABYTE * 16;
  }
  growth_step = mdbx_roundup2(growth_step, env->me_os_psize);
  if (bytes2pgno(env, growth_step) > UINT16_MAX)
    growth_step = pgno2bytes(env, UINT16_MAX);

  if (shrink_threshold < 0) {
    shrink_threshold = growth_step + growth_step;
    if (shrink_threshold < growth_step)
      shrink_threshold = growth_step;
  }
  shrink_threshold = mdbx_roundup2(shrink_threshold, env->me_os_psize);
  if (bytes2pgno(env, shrink_threshold) > UINT16_MAX)
    shrink_threshold = pgno2bytes(env, UINT16_MAX);

  /* save user's geo-params for future open/create */
  env->me_dbgeo.lower = size_lower;
  env->me_dbgeo.now = size_now;
  env->me_dbgeo.upper = size_upper;
  env->me_dbgeo.grow = growth_step;
  env->me_dbgeo.shrink = shrink_threshold;
  rc = MDBX_SUCCESS;

  if (env->me_map) {
    /* apply new params */
    mdbx_assert(env, pagesize == (intptr_t)env->me_psize);

    MDBX_meta *head = mdbx_meta_head(env);
    MDBX_meta meta = *head;
    meta.mm_geo.lower = bytes2pgno(env, env->me_dbgeo.lower);
    meta.mm_geo.now = bytes2pgno(env, env->me_dbgeo.now);
    meta.mm_geo.upper = bytes2pgno(env, env->me_dbgeo.upper);
    meta.mm_geo.grow = (uint16_t)bytes2pgno(env, env->me_dbgeo.grow);
    meta.mm_geo.shrink = (uint16_t)bytes2pgno(env, env->me_dbgeo.shrink);

    mdbx_assert(env, env->me_dbgeo.lower >= MIN_MAPSIZE);
    mdbx_assert(env, meta.mm_geo.lower >= MIN_PAGENO);
    mdbx_assert(env, env->me_dbgeo.upper <= MAX_MAPSIZE);
    mdbx_assert(env, meta.mm_geo.upper <= MAX_PAGENO);
    mdbx_assert(env, meta.mm_geo.now >= meta.mm_geo.next);
    mdbx_assert(env, env->me_dbgeo.upper >= env->me_dbgeo.lower);
    mdbx_assert(env, meta.mm_geo.upper >= meta.mm_geo.now);
    mdbx_assert(env, meta.mm_geo.now >= meta.mm_geo.lower);
    mdbx_assert(env, meta.mm_geo.grow == bytes2pgno(env, env->me_dbgeo.grow));
    mdbx_assert(env,
                meta.mm_geo.shrink == bytes2pgno(env, env->me_dbgeo.shrink));

    if (memcmp(&meta.mm_geo, &head->mm_geo, sizeof(meta.mm_geo))) {
      if (meta.mm_geo.now != head->mm_geo.now ||
          meta.mm_geo.upper != head->mm_geo.upper) {
        rc = mdbx_mapresize(env, meta.mm_geo.now, meta.mm_geo.upper);
        if (unlikely(rc != MDBX_SUCCESS))
          goto bailout;
      }
      mdbx_meta_set_txnid(env, &meta, mdbx_meta_txnid_stable(env, head) + 1);
      rc = mdbx_sync_locked(env, env->me_flags, &meta);
    }
  } else if (pagesize != (intptr_t)env->me_psize) {
    mdbx_setup_pagesize(env, pagesize);
  }

bailout:
  if (env->me_map && outside_txn)
    mdbx_txn_unlock(env);
  return rc;
}

int __cold mdbx_env_set_mapsize(MDBX_env *env, size_t size) {
  return mdbx_env_set_geometry(env, -1, size, -1, -1, -1, -1);
}

int __cold mdbx_env_set_maxdbs(MDBX_env *env, MDBX_dbi dbs) {
  if (unlikely(dbs > MAX_DBI))
    return MDBX_EINVAL;

  if (unlikely(!env))
    return MDBX_EINVAL;

  if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(env->me_map))
    return MDBX_EPERM;

  env->me_maxdbs = dbs + CORE_DBS;
  return MDBX_SUCCESS;
}

int __cold mdbx_env_set_maxreaders(MDBX_env *env, unsigned readers) {
  if (unlikely(readers < 1 || readers > INT16_MAX))
    return MDBX_EINVAL;

  if (unlikely(!env))
    return MDBX_EINVAL;

  if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(env->me_map))
    return MDBX_EPERM;

  env->me_maxreaders = readers;
  return MDBX_SUCCESS;
}

int __cold mdbx_env_get_maxreaders(MDBX_env *env, unsigned *readers) {
  if (!env || !readers)
    return MDBX_EINVAL;

  if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
    return MDBX_EBADSIGN;

  *readers = env->me_maxreaders;
  return MDBX_SUCCESS;
}

/* Further setup required for opening an MDBX environment */
static int __cold mdbx_setup_dxb(MDBX_env *env, int lck_rc) {
  MDBX_meta meta;
  int rc = MDBX_RESULT_FALSE;
  int err = mdbx_read_header(env, &meta);
  if (unlikely(err != MDBX_SUCCESS)) {
    if (lck_rc != /* lck exclusive */ MDBX_RESULT_TRUE || err != MDBX_ENODATA ||
        (env->me_flags & MDBX_RDONLY) != 0)
      return err;

    mdbx_debug("create new database");
    rc = /* new database */ MDBX_RESULT_TRUE;

    if (!env->me_dbgeo.now) {
      /* set defaults if not configured */
      err = mdbx_env_set_mapsize(env, DEFAULT_MAPSIZE);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
    }

    void *buffer = calloc(NUM_METAS, env->me_psize);
    if (!buffer)
      return MDBX_ENOMEM;

    meta = mdbx_init_metas(env, buffer)->mp_meta;
    err = mdbx_pwrite(env->me_fd, buffer, env->me_psize * NUM_METAS, 0);
    free(buffer);
    if (unlikely(err != MDBX_SUCCESS))
      return err;

    err = mdbx_ftruncate(env->me_fd, env->me_dbgeo.now);
    if (unlikely(err != MDBX_SUCCESS))
      return err;

#ifndef NDEBUG /* just for checking */
    err = mdbx_read_header(env, &meta);
    if (unlikely(err != MDBX_SUCCESS))
      return err;
#endif
  }

  mdbx_info("header: root %" PRIaPGNO "/%" PRIaPGNO ", geo %" PRIaPGNO
            "/%" PRIaPGNO "-%" PRIaPGNO "/%" PRIaPGNO
            " +%u -%u, txn_id %" PRIaTXN ", %s",
            meta.mm_dbs[MAIN_DBI].md_root, meta.mm_dbs[FREE_DBI].md_root,
            meta.mm_geo.lower, meta.mm_geo.next, meta.mm_geo.now,
            meta.mm_geo.upper, meta.mm_geo.grow, meta.mm_geo.shrink,
            meta.mm_txnid_a, mdbx_durable_str(&meta));

  mdbx_setup_pagesize(env, meta.mm_psize);
  if ((env->me_flags & MDBX_RDONLY) /* readonly */
      || lck_rc != MDBX_RESULT_TRUE /* not exclusive */) {
    /* use present params from db */
    err = mdbx_env_set_geometry(
        env, meta.mm_geo.lower * meta.mm_psize, meta.mm_geo.now * meta.mm_psize,
        meta.mm_geo.upper * meta.mm_psize, meta.mm_geo.grow * meta.mm_psize,
        meta.mm_geo.shrink * meta.mm_psize, meta.mm_psize);
    if (unlikely(err != MDBX_SUCCESS)) {
      mdbx_error("could not use present dbsize-params from db");
      return MDBX_INCOMPATIBLE;
    }
  } else if (env->me_dbgeo.now) {
    /* silently growth to last used page */
    const size_t used_bytes = pgno2bytes(env, meta.mm_geo.next);
    if (env->me_dbgeo.lower < used_bytes)
      env->me_dbgeo.lower = used_bytes;
    if (env->me_dbgeo.now < used_bytes)
      env->me_dbgeo.now = used_bytes;
    if (env->me_dbgeo.upper < used_bytes)
      env->me_dbgeo.upper = used_bytes;

    /* apply preconfigured params, but only if substantial changes:
     *  - upper or lower limit changes
     *  - shrink theshold or growth step
     * But ignore just chagne just a 'now/current' size. */
    if (bytes_align2os_bytes(env, env->me_dbgeo.upper) !=
            pgno_align2os_bytes(env, meta.mm_geo.upper) ||
        bytes_align2os_bytes(env, env->me_dbgeo.lower) !=
            pgno_align2os_bytes(env, meta.mm_geo.lower) ||
        bytes_align2os_bytes(env, env->me_dbgeo.shrink) !=
            pgno_align2os_bytes(env, meta.mm_geo.shrink) ||
        bytes_align2os_bytes(env, env->me_dbgeo.grow) !=
            pgno_align2os_bytes(env, meta.mm_geo.grow)) {

      if (env->me_dbgeo.shrink && env->me_dbgeo.now > used_bytes)
        /* pre-shrink if enabled */
        env->me_dbgeo.now = used_bytes + env->me_dbgeo.shrink -
                            used_bytes % env->me_dbgeo.shrink;

      err = mdbx_env_set_geometry(env, env->me_dbgeo.lower, env->me_dbgeo.now,
                                  env->me_dbgeo.upper, env->me_dbgeo.grow,
                                  env->me_dbgeo.shrink, meta.mm_psize);
      if (unlikely(err != MDBX_SUCCESS)) {
        mdbx_error("could not apply preconfigured dbsize-params to db");
        return MDBX_INCOMPATIBLE;
      }

      /* update meta fields */
      meta.mm_geo.now = bytes2pgno(env, env->me_dbgeo.now);
      meta.mm_geo.lower = bytes2pgno(env, env->me_dbgeo.lower);
      meta.mm_geo.upper = bytes2pgno(env, env->me_dbgeo.upper);
      meta.mm_geo.grow = (uint16_t)bytes2pgno(env, env->me_dbgeo.grow);
      meta.mm_geo.shrink = (uint16_t)bytes2pgno(env, env->me_dbgeo.shrink);

      mdbx_info("amended: root %" PRIaPGNO "/%" PRIaPGNO ", geo %" PRIaPGNO
                "/%" PRIaPGNO "-%" PRIaPGNO "/%" PRIaPGNO
                " +%u -%u, txn_id %" PRIaTXN ", %s",
                meta.mm_dbs[MAIN_DBI].md_root, meta.mm_dbs[FREE_DBI].md_root,
                meta.mm_geo.lower, meta.mm_geo.next, meta.mm_geo.now,
                meta.mm_geo.upper, meta.mm_geo.grow, meta.mm_geo.shrink,
                meta.mm_txnid_a, mdbx_durable_str(&meta));
    }
    mdbx_ensure(env, meta.mm_geo.now >= meta.mm_geo.next);
  }

  uint64_t filesize_before_mmap;
  err = mdbx_filesize(env->me_fd, &filesize_before_mmap);
  if (unlikely(err != MDBX_SUCCESS))
    return err;

  const size_t expected_bytes =
      mdbx_roundup2(pgno2bytes(env, meta.mm_geo.now), env->me_os_psize);
  const size_t used_bytes = pgno2bytes(env, meta.mm_geo.next);
  mdbx_ensure(env, expected_bytes >= used_bytes);
  if (filesize_before_mmap != expected_bytes) {
    if (lck_rc != /* lck exclusive */ MDBX_RESULT_TRUE) {
      mdbx_info("filesize mismatch (expect %" PRIuPTR "/%" PRIaPGNO
                ", have %" PRIu64 "/%" PRIaPGNO "), "
                "assume collision in non-exclusive mode",
                expected_bytes, bytes2pgno(env, expected_bytes),
                filesize_before_mmap,
                bytes2pgno(env, (size_t)filesize_before_mmap));
    } else {
      mdbx_notice("filesize mismatch (expect %" PRIuPTR "/%" PRIaPGNO
                  ", have %" PRIu64 "/%" PRIaPGNO ")",
                  expected_bytes, bytes2pgno(env, expected_bytes),
                  filesize_before_mmap,
                  bytes2pgno(env, (size_t)filesize_before_mmap));
      if (filesize_before_mmap < used_bytes) {
        mdbx_error("last-page beyond end-of-file (last %" PRIaPGNO
                   ", have %" PRIaPGNO ")",
                   meta.mm_geo.next,
                   bytes2pgno(env, (size_t)filesize_before_mmap));
        return MDBX_CORRUPTED;
      }

      if (env->me_flags & MDBX_RDONLY) {
        mdbx_notice("ignore filesize mismatch in readonly-mode");
      } else {
        mdbx_info("resize datafile to %" PRIu64 " bytes, %" PRIaPGNO " pages",
                  expected_bytes, bytes2pgno(env, expected_bytes));
        err = mdbx_ftruncate(env->me_fd, expected_bytes);
        if (unlikely(err != MDBX_SUCCESS)) {
          mdbx_error("error %d, while resize datafile to %" PRIu64
                     " bytes, %" PRIaPGNO " pages",
                     rc, expected_bytes, bytes2pgno(env, expected_bytes));
          return err;
        }
        filesize_before_mmap = expected_bytes;
      }
    }
  }

  err = mdbx_env_map(env, (lck_rc != /* lck exclusive */ MDBX_RESULT_TRUE)
                              ? 0
                              : expected_bytes);
  if (err != MDBX_SUCCESS)
    return err;

  const unsigned meta_clash_mask = mdbx_meta_eq_mask(env);
  if (meta_clash_mask) {
    mdbx_error("meta-pages are clashed: mask 0x%d", meta_clash_mask);
    return MDBX_WANNA_RECOVERY;
  }

  while (1) {
    MDBX_meta *head = mdbx_meta_head(env);
    const txnid_t head_txnid = mdbx_meta_txnid_fluid(env, head);
    if (head_txnid == meta.mm_txnid_a)
      break;

    if (lck_rc == /* lck exclusive */ MDBX_RESULT_TRUE) {
      assert(META_IS_STEADY(&meta) && !META_IS_STEADY(head));
      if (env->me_flags & MDBX_RDONLY) {
        mdbx_error("rollback needed: (from head %" PRIaTXN
                   " to steady %" PRIaTXN "), but unable in read-only mode",
                   head_txnid, meta.mm_txnid_a);
        return MDBX_WANNA_RECOVERY /* LY: could not recovery/rollback */;
      }

      /* LY: rollback weak checkpoint */
      mdbx_trace("rollback: from %" PRIaTXN ", to %" PRIaTXN, head_txnid,
                 meta.mm_txnid_a);
      mdbx_ensure(env, head_txnid == mdbx_meta_txnid_stable(env, head));

      if (env->me_flags & MDBX_WRITEMAP) {
        head->mm_txnid_a = 0;
        head->mm_datasync_sign = MDBX_DATASIGN_WEAK;
        head->mm_txnid_b = 0;
        const size_t offset =
            (uint8_t *)container_of(head, MDBX_page, mp_meta) -
            env->me_dxb_mmap.dxb;
        const size_t paged_offset = offset & ~(env->me_os_psize - 1);
        const size_t paged_length = mdbx_roundup2(
            env->me_psize + offset - paged_offset, env->me_os_psize);
        err = mdbx_msync(&env->me_dxb_mmap, paged_offset, paged_length, false);
      } else {
        MDBX_meta rollback = *head;
        mdbx_meta_set_txnid(env, &rollback, 0);
        rollback.mm_datasync_sign = MDBX_DATASIGN_WEAK;
        err = mdbx_pwrite(env->me_fd, &rollback, sizeof(MDBX_meta),
                          (uint8_t *)head - (uint8_t *)env->me_map);
      }
      if (err)
        return err;

      mdbx_invalidate_cache(env->me_map, pgno2bytes(env, NUM_METAS));
      mdbx_ensure(env, 0 == mdbx_meta_txnid_fluid(env, head));
      mdbx_ensure(env, 0 == mdbx_meta_eq_mask(env));
      continue;
    }

    if (!env->me_lck) {
      /* LY: without-lck (read-only) mode, so it is imposible that other
       * process made weak checkpoint. */
      mdbx_error("without-lck, unable recovery/rollback");
      return MDBX_WANNA_RECOVERY;
    }

    /* LY: assume just have a collision with other running process,
     *     or someone make a weak checkpoint */
    mdbx_info("assume collision or online weak checkpoint");
    break;
  }

  const MDBX_meta *head = mdbx_meta_head(env);
  if (lck_rc == /* lck exclusive */ MDBX_RESULT_TRUE) {
    /* re-check file size after mmap */
    uint64_t filesize_after_mmap;
    err = mdbx_filesize(env->me_fd, &filesize_after_mmap);
    if (unlikely(err != MDBX_SUCCESS))
      return err;
    if (filesize_after_mmap != expected_bytes) {
      if (filesize_after_mmap != filesize_before_mmap)
        mdbx_info("datafile resized by system to %" PRIu64 " bytes",
                  filesize_after_mmap);
      if (filesize_after_mmap % env->me_os_psize ||
          filesize_after_mmap > env->me_dbgeo.upper ||
          filesize_after_mmap < used_bytes) {
        mdbx_info("unacceptable/unexpected  datafile size %" PRIu64,
                  filesize_after_mmap);
        return MDBX_PROBLEM;
      }
      if ((env->me_flags & MDBX_RDONLY) == 0) {
        meta.mm_geo.now =
            bytes2pgno(env, env->me_dbgeo.now = (size_t)filesize_after_mmap);
        mdbx_info("update meta-geo to filesize %" PRIuPTR " bytes, %" PRIaPGNO
                  " pages",
                  env->me_dbgeo.now, meta.mm_geo.now);
      }
    }

    if (memcmp(&meta.mm_geo, &head->mm_geo, sizeof(meta.mm_geo))) {
      const txnid_t txnid = mdbx_meta_txnid_stable(env, head);
      mdbx_info("updating meta.geo: "
                "from l%" PRIaPGNO "-n%" PRIaPGNO "-u%" PRIaPGNO
                "/s%u-g%u (txn#%" PRIaTXN "), "
                "to l%" PRIaPGNO "-n%" PRIaPGNO "-u%" PRIaPGNO
                "/s%u-g%u (txn#%" PRIaTXN ")",
                head->mm_geo.lower, head->mm_geo.now, head->mm_geo.upper,
                head->mm_geo.shrink, head->mm_geo.grow, txnid,
                meta.mm_geo.lower, meta.mm_geo.now, meta.mm_geo.upper,
                meta.mm_geo.shrink, meta.mm_geo.grow, txnid + 1);

      mdbx_ensure(env, mdbx_meta_eq(env, &meta, head));
      mdbx_meta_set_txnid(env, &meta, txnid + 1);
      env->me_sync_pending += env->me_psize;
      err = mdbx_sync_locked(env, env->me_flags | MDBX_SHRINK_ALLOWED, &meta);
      if (err) {
        mdbx_info("error %d, while updating meta.geo: "
                  "from l%" PRIaPGNO "-n%" PRIaPGNO "-u%" PRIaPGNO
                  "/s%u-g%u (txn#%" PRIaTXN "), "
                  "to l%" PRIaPGNO "-n%" PRIaPGNO "-u%" PRIaPGNO
                  "/s%u-g%u (txn#%" PRIaTXN ")",
                  err, head->mm_geo.lower, head->mm_geo.now, head->mm_geo.upper,
                  head->mm_geo.shrink, head->mm_geo.grow, txnid,
                  meta.mm_geo.lower, meta.mm_geo.now, meta.mm_geo.upper,
                  meta.mm_geo.shrink, meta.mm_geo.grow, txnid + 1);
        return err;
      }
    }
  }

  return rc;
}

/****************************************************************************/

/* Open and/or initialize the lock region for the environment. */
static int __cold mdbx_setup_lck(MDBX_env *env, char *lck_pathname, int mode) {
  assert(env->me_fd != INVALID_HANDLE_VALUE);
  assert(env->me_lfd == INVALID_HANDLE_VALUE);

  int err = mdbx_openfile(lck_pathname, O_RDWR | O_CREAT, mode, &env->me_lfd);
  if (err != MDBX_SUCCESS) {
    if (err != MDBX_EROFS || (env->me_flags & MDBX_RDONLY) == 0)
      return err;
    /* LY: without-lck mode (e.g. on read-only filesystem) */
    env->me_lfd = INVALID_HANDLE_VALUE;
    env->me_oldest = &env->me_oldest_stub;
    env->me_maxreaders = UINT_MAX;
    mdbx_debug("lck-setup: %s ", "lockless mode (readonly)");
    return MDBX_SUCCESS;
  }

  /* Try to get exclusive lock. If we succeed, then
   * nobody is using the lock region and we should initialize it. */
  const int rc = mdbx_lck_seize(env);
  if (MDBX_IS_ERROR(rc))
    return rc;

  mdbx_debug("lck-setup: %s ",
             (rc == MDBX_RESULT_TRUE) ? "exclusive" : "shared");

  uint64_t size;
  err = mdbx_filesize(env->me_lfd, &size);
  if (unlikely(err != MDBX_SUCCESS))
    return err;

  if (rc == MDBX_RESULT_TRUE) {
    uint64_t wanna = mdbx_roundup2(
        (env->me_maxreaders - 1) * sizeof(MDBX_reader) + sizeof(MDBX_lockinfo),
        env->me_os_psize);
#ifndef NDEBUG
    err = mdbx_ftruncate(env->me_lfd, size = 0);
    if (unlikely(err != MDBX_SUCCESS))
      return err;
#endif
    mdbx_jitter4testing(false);

    if (size != wanna) {
      err = mdbx_ftruncate(env->me_lfd, wanna);
      if (unlikely(err != MDBX_SUCCESS))
        return err;
      size = wanna;
    }
  } else if (size > SSIZE_MAX || (size & (env->me_os_psize - 1)) ||
             size < env->me_os_psize) {
    mdbx_notice("lck-file has invalid size %" PRIu64 " bytes", size);
    return MDBX_PROBLEM;
  }

  const size_t maxreaders =
      ((size_t)size - sizeof(MDBX_lockinfo)) / sizeof(MDBX_reader) + 1;
  if (maxreaders > UINT16_MAX) {
    mdbx_error("lck-size too big (up to %" PRIuPTR " readers)", maxreaders);
    return MDBX_PROBLEM;
  }
  env->me_maxreaders = (unsigned)maxreaders;

  err = mdbx_mmap(MDBX_WRITEMAP, &env->me_lck_mmap, (size_t)size, (size_t)size);
  if (unlikely(err != MDBX_SUCCESS))
    return err;

#ifdef MADV_DODUMP
  (void)madvise(env->me_lck, size, MADV_DODUMP);
#endif

#ifdef MADV_DONTFORK
  if (madvise(env->me_lck, size, MADV_DONTFORK) < 0)
    return errno;
#endif

#ifdef MADV_WILLNEED
  if (madvise(env->me_lck, size, MADV_WILLNEED) < 0)
    return errno;
#endif

#ifdef MADV_RANDOM
  if (madvise(env->me_lck, size, MADV_RANDOM) < 0)
    return errno;
#endif

  if (rc == MDBX_RESULT_TRUE) {
    /* LY: exlcusive mode, init lck */
    memset(env->me_lck, 0, (size_t)size);
    err = mdbx_lck_init(env);
    if (err)
      return err;

    env->me_lck->mti_magic_and_version = MDBX_LOCK_MAGIC;
    env->me_lck->mti_os_and_format = MDBX_LOCK_FORMAT;
  } else {
    if (env->me_lck->mti_magic_and_version != MDBX_LOCK_MAGIC) {
      mdbx_error("lock region has invalid magic/version");
      return ((env->me_lck->mti_magic_and_version >> 8) != MDBX_MAGIC)
                 ? MDBX_INVALID
                 : MDBX_VERSION_MISMATCH;
    }
    if (env->me_lck->mti_os_and_format != MDBX_LOCK_FORMAT) {
      mdbx_error("lock region has os/format 0x%" PRIx32 ", expected 0x%" PRIx32,
                 env->me_lck->mti_os_and_format, MDBX_LOCK_FORMAT);
      return MDBX_VERSION_MISMATCH;
    }
  }

  mdbx_assert(env, !MDBX_IS_ERROR(rc));
  env->me_oldest = &env->me_lck->mti_oldest;
  return rc;
}

/* Only a subset of the mdbx_env flags can be changed
 * at runtime. Changing other flags requires closing the
 * environment and re-opening it with the new flags. */
#define CHANGEABLE                                                             \
  (MDBX_NOSYNC | MDBX_NOMETASYNC | MDBX_MAPASYNC | MDBX_NOMEMINIT |            \
   MDBX_COALESCE | MDBX_PAGEPERTURB)
#define CHANGELESS                                                             \
  (MDBX_NOSUBDIR | MDBX_RDONLY | MDBX_WRITEMAP | MDBX_NOTLS | MDBX_NORDAHEAD | \
   MDBX_LIFORECLAIM)

#if VALID_FLAGS & PERSISTENT_FLAGS & (CHANGEABLE | CHANGELESS)
#error "Persistent DB flags & env flags overlap, but both go in mm_flags"
#endif

int __cold mdbx_env_open_ex(MDBX_env *env, const char *path, unsigned flags,
                            mode_t mode, int *exclusive) {
  if (unlikely(!env || !path))
    return MDBX_EINVAL;

  if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
    return MDBX_EBADSIGN;

  if (env->me_fd != INVALID_HANDLE_VALUE ||
      (flags & ~(CHANGEABLE | CHANGELESS)))
    return MDBX_EINVAL;

  size_t len_full, len = strlen(path);
  if (flags & MDBX_NOSUBDIR) {
    len_full = len + sizeof(MDBX_LOCK_SUFFIX) + len + 1;
  } else {
    len_full = len + sizeof(MDBX_LOCKNAME) + len + sizeof(MDBX_DATANAME);
  }
  char *lck_pathname = malloc(len_full);
  if (!lck_pathname)
    return MDBX_ENOMEM;

  char *dxb_pathname;
  if (flags & MDBX_NOSUBDIR) {
    dxb_pathname = lck_pathname + len + sizeof(MDBX_LOCK_SUFFIX);
    sprintf(lck_pathname, "%s" MDBX_LOCK_SUFFIX, path);
    strcpy(dxb_pathname, path);
  } else {
    dxb_pathname = lck_pathname + len + sizeof(MDBX_LOCKNAME);
    sprintf(lck_pathname, "%s" MDBX_LOCKNAME, path);
    sprintf(dxb_pathname, "%s" MDBX_DATANAME, path);
  }

  int rc = MDBX_SUCCESS;
  flags |= env->me_flags;
  if (flags & MDBX_RDONLY) {
    /* LY: silently ignore irrelevant flags when
     * we're only getting read access */
    flags &= ~(MDBX_WRITEMAP | MDBX_MAPASYNC | MDBX_NOSYNC | MDBX_NOMETASYNC |
               MDBX_COALESCE | MDBX_LIFORECLAIM | MDBX_NOMEMINIT);
  } else {
    if (!((env->me_free_pgs = mdbx_pnl_alloc(MDBX_PNL_UM_MAX)) &&
          (env->me_dirtylist = calloc(MDBX_PNL_UM_SIZE, sizeof(MDBX_ID2)))))
      rc = MDBX_ENOMEM;
  }
  env->me_flags = flags |= MDBX_ENV_ACTIVE;
  if (rc)
    goto bailout;

  env->me_path = mdbx_strdup(path);
  env->me_dbxs = calloc(env->me_maxdbs, sizeof(MDBX_dbx));
  env->me_dbflags = calloc(env->me_maxdbs, sizeof(uint16_t));
  env->me_dbiseqs = calloc(env->me_maxdbs, sizeof(unsigned));
  if (!(env->me_dbxs && env->me_path && env->me_dbflags && env->me_dbiseqs)) {
    rc = MDBX_ENOMEM;
    goto bailout;
  }
  env->me_dbxs[FREE_DBI].md_cmp = mdbx_cmp_int_ai; /* aligned MDBX_INTEGERKEY */

  int oflags;
  if (F_ISSET(flags, MDBX_RDONLY))
    oflags = O_RDONLY;
  else
    oflags = O_RDWR | O_CREAT;

  rc = mdbx_openfile(dxb_pathname, oflags, mode, &env->me_fd);
  if (rc != MDBX_SUCCESS)
    goto bailout;

  const int lck_rc = mdbx_setup_lck(env, lck_pathname, mode);
  if (MDBX_IS_ERROR(lck_rc)) {
    rc = lck_rc;
    goto bailout;
  }

  const int dxb_rc = mdbx_setup_dxb(env, lck_rc);
  if (MDBX_IS_ERROR(dxb_rc)) {
    rc = dxb_rc;
    goto bailout;
  }

  mdbx_debug("opened dbenv %p", (void *)env);
  const unsigned mode_flags =
      MDBX_WRITEMAP | MDBX_NOSYNC | MDBX_NOMETASYNC | MDBX_MAPASYNC;
  if (lck_rc == MDBX_RESULT_TRUE) {
    env->me_lck->mti_envmode = env->me_flags & (mode_flags | MDBX_RDONLY);
    if (exclusive == NULL || *exclusive < 2) {
      /* LY: downgrade lock only if exclusive access not requested.
       *     in case exclusive==1, just leave value as is. */
      rc = mdbx_lck_downgrade(env, true);
      mdbx_debug("lck-downgrade-full: rc %i ", rc);
    } else {
      rc = mdbx_lck_downgrade(env, false);
      mdbx_debug("lck-downgrade-partial: rc %i ", rc);
    }
    if (rc != MDBX_SUCCESS)
      goto bailout;
  } else {
    if (exclusive) {
      /* LY: just indicate that is not an exclusive access. */
      *exclusive = 0;
    }
    if ((env->me_flags & MDBX_RDONLY) == 0) {
      while (env->me_lck->mti_envmode == MDBX_RDONLY) {
        if (mdbx_atomic_compare_and_swap32(&env->me_lck->mti_envmode,
                                           MDBX_RDONLY,
                                           env->me_flags & mode_flags))
          break;
        /* TODO: yield/relax cpu */
      }
      if ((env->me_lck->mti_envmode ^ env->me_flags) & mode_flags) {
        mdbx_error("current mode/flags incompatible with requested");
        rc = MDBX_INCOMPATIBLE;
        goto bailout;
      }
    }
  }

  if (env->me_lck && (env->me_flags & MDBX_NOTLS) == 0) {
    rc = mdbx_rthc_alloc(&env->me_txkey, &env->me_lck->mti_readers[0],
                         &env->me_lck->mti_readers[env->me_maxreaders]);
    if (unlikely(rc != MDBX_SUCCESS))
      goto bailout;
    env->me_flags |= MDBX_ENV_TXKEY;
  }

  if ((flags & MDBX_RDONLY) == 0) {
    MDBX_txn *txn;
    int tsize = sizeof(MDBX_txn),
        size = tsize +
               env->me_maxdbs * (sizeof(MDBX_db) + sizeof(MDBX_cursor *) +
                                 sizeof(unsigned) + 1);
    if ((env->me_pbuf = calloc(1, env->me_psize)) && (txn = calloc(1, size))) {
      txn->mt_dbs = (MDBX_db *)((char *)txn + tsize);
      txn->mt_cursors = (MDBX_cursor **)(txn->mt_dbs + env->me_maxdbs);
      txn->mt_dbiseqs = (unsigned *)(txn->mt_cursors + env->me_maxdbs);
      txn->mt_dbflags = (uint8_t *)(txn->mt_dbiseqs + env->me_maxdbs);
      txn->mt_env = env;
      txn->mt_dbxs = env->me_dbxs;
      txn->mt_flags = MDBX_TXN_FINISHED;
      env->me_txn0 = txn;
    } else {
      rc = MDBX_ENOMEM;
    }
  }

#if MDBX_DEBUG
  if (rc == MDBX_SUCCESS) {
    MDBX_meta *meta = mdbx_meta_head(env);
    MDBX_db *db = &meta->mm_dbs[MAIN_DBI];

    mdbx_debug("opened database version %u, pagesize %u",
               (uint8_t)meta->mm_magic_and_version, env->me_psize);
    mdbx_debug("using meta page %" PRIaPGNO ", txn %" PRIaTXN "",
               container_of(meta, MDBX_page, mp_data)->mp_pgno,
               mdbx_meta_txnid_fluid(env, meta));
    mdbx_debug("depth: %u", db->md_depth);
    mdbx_debug("entries: %" PRIu64 "", db->md_entries);
    mdbx_debug("branch pages: %" PRIaPGNO "", db->md_branch_pages);
    mdbx_debug("leaf pages: %" PRIaPGNO "", db->md_leaf_pages);
    mdbx_debug("overflow pages: %" PRIaPGNO "", db->md_overflow_pages);
    mdbx_debug("root: %" PRIaPGNO "", db->md_root);
  }
#endif

bailout:
  if (rc)
    mdbx_env_close0(env);
  free(lck_pathname);
  return rc;
}

int __cold mdbx_env_open(MDBX_env *env, const char *path, unsigned flags,
                         mode_t mode) {
  return mdbx_env_open_ex(env, path, flags, mode, NULL);
}

/* Destroy resources from mdbx_env_open(), clear our readers & DBIs */
static void __cold mdbx_env_close0(MDBX_env *env) {
  if (!(env->me_flags & MDBX_ENV_ACTIVE))
    return;
  env->me_flags &= ~MDBX_ENV_ACTIVE;

  /* Doing this here since me_dbxs may not exist during mdbx_env_close */
  if (env->me_dbxs) {
    for (unsigned i = env->me_maxdbs; --i >= CORE_DBS;)
      free(env->me_dbxs[i].md_name.iov_base);
    free(env->me_dbxs);
  }

  free(env->me_pbuf);
  free(env->me_dbiseqs);
  free(env->me_dbflags);
  free(env->me_path);
  free(env->me_dirtylist);
  if (env->me_txn0) {
    mdbx_txl_free(env->me_txn0->mt_lifo_reclaimed);
    free(env->me_txn0);
  }
  mdbx_pnl_free(env->me_free_pgs);

  if (env->me_flags & MDBX_ENV_TXKEY) {
    mdbx_rthc_remove(env->me_txkey);
    env->me_flags &= ~MDBX_ENV_TXKEY;
  }

  if (env->me_map) {
    mdbx_munmap(&env->me_dxb_mmap);
#ifdef USE_VALGRIND
    VALGRIND_DISCARD(env->me_valgrind_handle);
    env->me_valgrind_handle = -1;
#endif
  }
  if (env->me_fd != INVALID_HANDLE_VALUE) {
    (void)mdbx_closefile(env->me_fd);
    env->me_fd = INVALID_HANDLE_VALUE;
  }

  if (env->me_lck)
    mdbx_munmap(&env->me_lck_mmap);
  env->me_pid = 0;
  env->me_oldest = nullptr;

  mdbx_lck_destroy(env);
  if (env->me_lfd != INVALID_HANDLE_VALUE) {
    (void)mdbx_closefile(env->me_lfd);
    env->me_lfd = INVALID_HANDLE_VALUE;
  }
}

int __cold mdbx_env_close_ex(MDBX_env *env, int dont_sync) {
  MDBX_page *dp;
  int rc = MDBX_SUCCESS;

  if (unlikely(!env))
    return MDBX_EINVAL;
  if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
    return MDBX_EBADSIGN;

  if (!dont_sync && !(env->me_flags & MDBX_RDONLY))
    rc = mdbx_env_sync(env, true);

  VALGRIND_DESTROY_MEMPOOL(env);
  while ((dp = env->me_dpages) != NULL) {
    ASAN_UNPOISON_MEMORY_REGION(&dp->mp_next, sizeof(dp->mp_next));
    VALGRIND_MAKE_MEM_DEFINED(&dp->mp_next, sizeof(dp->mp_next));
    env->me_dpages = dp->mp_next;
    free(dp);
  }

  mdbx_env_close0(env);
  mdbx_ensure(env, mdbx_fastmutex_destroy(&env->me_dbi_lock) == MDBX_SUCCESS);
  env->me_signature = 0;
  free(env);

  return rc;
}

void __cold mdbx_env_close(MDBX_env *env) { mdbx_env_close_ex(env, 0); }

/* Compare two items pointing at aligned unsigned int's. */
static int __hot mdbx_cmp_int_ai(const MDBX_val *a, const MDBX_val *b) {
  mdbx_assert(NULL, a->iov_len == b->iov_len);
  mdbx_assert(NULL, 0 == (uintptr_t)a->iov_base % sizeof(int) &&
                        0 == (uintptr_t)b->iov_base % sizeof(int));
  switch (a->iov_len) {
  case 4:
    return mdbx_cmp2int(*(uint32_t *)a->iov_base, *(uint32_t *)b->iov_base);
  case 8:
    return mdbx_cmp2int(*(uint64_t *)a->iov_base, *(uint64_t *)b->iov_base);
  default:
    mdbx_assert_fail(NULL, "invalid size for INTEGERKEY/INTEGERDUP", mdbx_func_,
                     __LINE__);
    return 0;
  }
}

/* Compare two items pointing at 2-byte aligned unsigned int's. */
static int __hot mdbx_cmp_int_a2(const MDBX_val *a, const MDBX_val *b) {
  mdbx_assert(NULL, a->iov_len == b->iov_len);
  mdbx_assert(NULL, 0 == (uintptr_t)a->iov_base % sizeof(uint16_t) &&
                        0 == (uintptr_t)b->iov_base % sizeof(uint16_t));
#if UNALIGNED_OK
  switch (a->iov_len) {
  case 4:
    return mdbx_cmp2int(*(uint32_t *)a->iov_base, *(uint32_t *)b->iov_base);
  case 8:
    return mdbx_cmp2int(*(uint64_t *)a->iov_base, *(uint64_t *)b->iov_base);
  default:
    mdbx_assert_fail(NULL, "invalid size for INTEGERKEY/INTEGERDUP", mdbx_func_,
                     __LINE__);
    return 0;
  }
#else
  mdbx_assert(NULL, 0 == a->iov_len % sizeof(uint16_t));
  {
    int diff;
    const uint16_t *pa, *pb, *end;

#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
    end = (const uint16_t *)a->iov_base;
    pa = (const uint16_t *)((char *)a->iov_base + a->iov_len);
    pb = (const uint16_t *)((char *)b->iov_base + a->iov_len);
    do {
      diff = *--pa - *--pb;
#else  /* __BYTE_ORDER__ */
    end = (const uint16_t *)((char *)a->iov_base + a->iov_len);
    pa = (const uint16_t *)a->iov_base;
    pb = (const uint16_t *)b->iov_base;
    do {
      diff = *pa++ - *pb++;
#endif /* __BYTE_ORDER__ */
      if (likely(diff != 0))
        break;
    } while (pa != end);
    return diff;
  }
#endif /* UNALIGNED_OK */
}

/* Compare two items pointing at unsigneds of unknown alignment.
 *
 * This is also set as MDBX_INTEGERDUP|MDBX_DUPFIXED's MDBX_dbx.md_dcmp. */
static int __hot mdbx_cmp_int_ua(const MDBX_val *a, const MDBX_val *b) {
  mdbx_assert(NULL, a->iov_len == b->iov_len);
#if UNALIGNED_OK
  switch (a->iov_len) {
  case 4:
    return mdbx_cmp2int(*(uint32_t *)a->iov_base, *(uint32_t *)b->iov_base);
  case 8:
    return mdbx_cmp2int(*(uint64_t *)a->iov_base, *(uint64_t *)b->iov_base);
  default:
    mdbx_assert_fail(NULL, "invalid size for INTEGERKEY/INTEGERDUP", mdbx_func_,
                     __LINE__);
    return 0;
  }
#else
  mdbx_assert(NULL, a->iov_len == sizeof(int) || a->iov_len == sizeof(size_t));
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
  {
    int diff;
    const uint8_t *pa, *pb;

    pa = (const uint8_t *)a->iov_base + a->iov_len;
    pb = (const uint8_t *)b->iov_base + a->iov_len;

    do {
      diff = *--pa - *--pb;
      if (likely(diff != 0))
        break;
    } while (pa != a->iov_base);
    return diff;
  }
#else /* __BYTE_ORDER__ */
  return memcmp(a->iov_base, b->iov_base, a->iov_len);
#endif /* __BYTE_ORDER__ */
#endif /* UNALIGNED_OK */
}

/* Compare two items lexically */
static int __hot mdbx_cmp_memn(const MDBX_val *a, const MDBX_val *b) {
/* LY: assumes that length of keys are NOT equal for most cases,
 * if no then branch-prediction should mitigate the problem */
#if 0
  /* LY: without branch instructions on x86,
   * but isn't best for equal length of keys */
  int diff_len = mdbx_cmp2int(a->iov_len, b->iov_len);
#else
  /* LY: best when length of keys are equal,
   * but got a branch-penalty otherwise */
  if (likely(a->iov_len == b->iov_len))
    return memcmp(a->iov_base, b->iov_base, a->iov_len);
  int diff_len = (a->iov_len < b->iov_len) ? -1 : 1;
#endif
  size_t shortest = (a->iov_len < b->iov_len) ? a->iov_len : b->iov_len;
  int diff_data = memcmp(a->iov_base, b->iov_base, shortest);
  return likely(diff_data) ? diff_data : diff_len;
}

/* Compare two items in reverse byte order */
static int __hot mdbx_cmp_memnr(const MDBX_val *a, const MDBX_val *b) {
  const uint8_t *pa, *pb, *end;

  pa = (const uint8_t *)a->iov_base + a->iov_len;
  pb = (const uint8_t *)b->iov_base + b->iov_len;
  size_t minlen = (a->iov_len < b->iov_len) ? a->iov_len : b->iov_len;
  end = pa - minlen;

  while (pa != end) {
    int diff = *--pa - *--pb;
    if (likely(diff))
      return diff;
  }
  return mdbx_cmp2int(a->iov_len, b->iov_len);
}

/* Search for key within a page, using binary search.
 * Returns the smallest entry larger or equal to the key.
 * If exactp is non-null, stores whether the found entry was an exact match
 * in *exactp (1 or 0).
 * Updates the cursor index with the index of the found entry.
 * If no entry larger or equal to the key is found, returns NULL. */
static MDBX_node *__hot mdbx_node_search(MDBX_cursor *mc, MDBX_val *key,
                                         int *exactp) {
  unsigned i = 0, nkeys;
  int low, high;
  int rc = 0;
  MDBX_page *mp = mc->mc_pg[mc->mc_top];
  MDBX_node *node = NULL;
  MDBX_val nodekey;
  MDBX_cmp_func *cmp;
  DKBUF;

  nkeys = NUMKEYS(mp);

  mdbx_debug("searching %u keys in %s %spage %" PRIaPGNO "", nkeys,
             IS_LEAF(mp) ? "leaf" : "branch", IS_SUBP(mp) ? "sub-" : "",
             mp->mp_pgno);

  low = IS_LEAF(mp) ? 0 : 1;
  high = nkeys - 1;
  cmp = mc->mc_dbx->md_cmp;

  /* Branch pages have no data, so if using integer keys,
   * alignment is guaranteed. Use faster mdbx_cmp_int_ai.
   */
  if (cmp == mdbx_cmp_int_a2 && IS_BRANCH(mp))
    cmp = mdbx_cmp_int_ai;

  if (IS_LEAF2(mp)) {
    nodekey.iov_len = mc->mc_db->md_xsize;
    node = NODEPTR(mp, 0); /* fake */
    while (low <= high) {
      i = (low + high) >> 1;
      nodekey.iov_base = LEAF2KEY(mp, i, nodekey.iov_len);
      rc = cmp(key, &nodekey);
      mdbx_debug("found leaf index %u [%s], rc = %i", i, DKEY(&nodekey), rc);
      if (rc == 0)
        break;
      if (rc > 0)
        low = i + 1;
      else
        high = i - 1;
    }
  } else {
    while (low <= high) {
      i = (low + high) >> 1;

      node = NODEPTR(mp, i);
      nodekey.iov_len = NODEKSZ(node);
      nodekey.iov_base = NODEKEY(node);

      rc = cmp(key, &nodekey);
      if (IS_LEAF(mp))
        mdbx_debug("found leaf index %u [%s], rc = %i", i, DKEY(&nodekey), rc);
      else
        mdbx_debug("found branch index %u [%s -> %" PRIaPGNO "], rc = %i", i,
                   DKEY(&nodekey), NODEPGNO(node), rc);
      if (rc == 0)
        break;
      if (rc > 0)
        low = i + 1;
      else
        high = i - 1;
    }
  }

  if (rc > 0) /* Found entry is less than the key. */
    i++;      /* Skip to get the smallest entry larger than key. */

  if (exactp)
    *exactp = (rc == 0 && nkeys > 0);
  /* store the key index */
  mdbx_cassert(mc, i <= UINT16_MAX);
  mc->mc_ki[mc->mc_top] = (indx_t)i;
  if (i >= nkeys)
    /* There is no entry larger or equal to the key. */
    return NULL;

  /* nodeptr is fake for LEAF2 */
  return IS_LEAF2(mp) ? node : NODEPTR(mp, i);
}

#if 0 /* unused for now */
static void mdbx_cursor_adjust(MDBX_cursor *mc, func) {
  MDBX_cursor *m2;

  for (m2 = mc->mc_txn->mt_cursors[mc->mc_dbi]; m2; m2 = m2->mc_next) {
    if (m2->mc_pg[m2->mc_top] == mc->mc_pg[mc->mc_top]) {
      func(mc, m2);
    }
  }
}
#endif

/* Pop a page off the top of the cursor's stack. */
static void mdbx_cursor_pop(MDBX_cursor *mc) {
  if (mc->mc_snum) {
    mdbx_debug("popped page %" PRIaPGNO " off db %d cursor %p",
               mc->mc_pg[mc->mc_top]->mp_pgno, DDBI(mc), (void *)mc);

    mc->mc_snum--;
    if (mc->mc_snum) {
      mc->mc_top--;
    } else {
      mc->mc_flags &= ~C_INITIALIZED;
    }
  }
}

/* Push a page onto the top of the cursor's stack.
 * Set MDBX_TXN_ERROR on failure. */
static int mdbx_cursor_push(MDBX_cursor *mc, MDBX_page *mp) {
  mdbx_debug("pushing page %" PRIaPGNO " on db %d cursor %p", mp->mp_pgno,
             DDBI(mc), (void *)mc);

  if (unlikely(mc->mc_snum >= CURSOR_STACK)) {
    mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
    return MDBX_CURSOR_FULL;
  }

  mdbx_cassert(mc, mc->mc_snum < UINT16_MAX);
  mc->mc_top = mc->mc_snum++;
  mc->mc_pg[mc->mc_top] = mp;
  mc->mc_ki[mc->mc_top] = 0;

  return MDBX_SUCCESS;
}

/* Find the address of the page corresponding to a given page number.
 * Set MDBX_TXN_ERROR on failure.
 *
 * [in] mc    the cursor accessing the page.
 * [in] pgno  the page number for the page to retrieve.
 * [out] ret  address of a pointer where the page's address will be
 *            stored.
 * [out] lvl  dirtylist inheritance level of found page. 1=current txn,
 *            0=mapped page.
 *
 * Returns 0 on success, non-zero on failure. */
static int mdbx_page_get(MDBX_cursor *mc, pgno_t pgno, MDBX_page **ret,
                         int *lvl) {
  MDBX_txn *txn = mc->mc_txn;
  MDBX_env *env = txn->mt_env;
  MDBX_page *p = NULL;
  int level;

  if (!(txn->mt_flags & (MDBX_TXN_RDONLY | MDBX_TXN_WRITEMAP))) {
    MDBX_txn *tx2 = txn;
    level = 1;
    do {
      MDBX_ID2L dl = tx2->mt_rw_dirtylist;
      unsigned x;
      /* Spilled pages were dirtied in this txn and flushed
       * because the dirty list got full. Bring this page
       * back in from the map (but don't unspill it here,
       * leave that unless page_touch happens again). */
      if (tx2->mt_spill_pages) {
        pgno_t pn = pgno << 1;
        x = mdbx_pnl_search(tx2->mt_spill_pages, pn);
        if (x <= tx2->mt_spill_pages[0] && tx2->mt_spill_pages[x] == pn)
          goto mapped;
      }
      if (dl[0].mid) {
        unsigned y = mdbx_mid2l_search(dl, pgno);
        if (y <= dl[0].mid && dl[y].mid == pgno) {
          p = dl[y].mptr;
          goto done;
        }
      }
      level++;
    } while ((tx2 = tx2->mt_parent) != NULL);
  }

  if (unlikely(pgno >= txn->mt_next_pgno)) {
    mdbx_debug("page %" PRIaPGNO " not found", pgno);
    txn->mt_flags |= MDBX_TXN_ERROR;
    return MDBX_PAGE_NOTFOUND;
  }
  level = 0;

mapped:
  p = pgno2page(env, pgno);
/* TODO: check p->mp_validator here */

done:
  *ret = p;
  if (lvl)
    *lvl = level;
  return MDBX_SUCCESS;
}

/* Finish mdbx_page_search() / mdbx_page_search_lowest().
 * The cursor is at the root page, set up the rest of it. */
static int mdbx_page_search_root(MDBX_cursor *mc, MDBX_val *key, int flags) {
  MDBX_page *mp = mc->mc_pg[mc->mc_top];
  int rc;
  DKBUF;

  while (IS_BRANCH(mp)) {
    MDBX_node *node;
    indx_t i;

    mdbx_debug("branch page %" PRIaPGNO " has %u keys", mp->mp_pgno,
               NUMKEYS(mp));
    /* Don't assert on branch pages in the FreeDB. We can get here
     * while in the process of rebalancing a FreeDB branch page; we must
     * let that proceed. ITS#8336 */
    mdbx_cassert(mc, !mc->mc_dbi || NUMKEYS(mp) > 1);
    mdbx_debug("found index 0 to page %" PRIaPGNO "", NODEPGNO(NODEPTR(mp, 0)));

    if (flags & (MDBX_PS_FIRST | MDBX_PS_LAST)) {
      i = 0;
      if (flags & MDBX_PS_LAST) {
        i = NUMKEYS(mp) - 1;
        /* if already init'd, see if we're already in right place */
        if (mc->mc_flags & C_INITIALIZED) {
          if (mc->mc_ki[mc->mc_top] == i) {
            mc->mc_top = mc->mc_snum++;
            mp = mc->mc_pg[mc->mc_top];
            goto ready;
          }
        }
      }
    } else {
      int exact;
      node = mdbx_node_search(mc, key, &exact);
      if (node == NULL)
        i = NUMKEYS(mp) - 1;
      else {
        i = mc->mc_ki[mc->mc_top];
        if (!exact) {
          mdbx_cassert(mc, i > 0);
          i--;
        }
      }
      mdbx_debug("following index %u for key [%s]", i, DKEY(key));
    }

    mdbx_cassert(mc, i < NUMKEYS(mp));
    node = NODEPTR(mp, i);

    if (unlikely((rc = mdbx_page_get(mc, NODEPGNO(node), &mp, NULL)) != 0))
      return rc;

    mc->mc_ki[mc->mc_top] = i;
    if (unlikely(rc = mdbx_cursor_push(mc, mp)))
      return rc;

  ready:
    if (flags & MDBX_PS_MODIFY) {
      if (unlikely((rc = mdbx_page_touch(mc)) != 0))
        return rc;
      mp = mc->mc_pg[mc->mc_top];
    }
  }

  if (unlikely(!IS_LEAF(mp))) {
    mdbx_debug("internal error, index points to a page with 0x%02x flags!?",
               mp->mp_flags);
    mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
    return MDBX_CORRUPTED;
  }

  mdbx_debug("found leaf page %" PRIaPGNO " for key [%s]", mp->mp_pgno,
             DKEY(key));
  mc->mc_flags |= C_INITIALIZED;
  mc->mc_flags &= ~C_EOF;

  return MDBX_SUCCESS;
}

/* Search for the lowest key under the current branch page.
 * This just bypasses a NUMKEYS check in the current page
 * before calling mdbx_page_search_root(), because the callers
 * are all in situations where the current page is known to
 * be underfilled. */
static int mdbx_page_search_lowest(MDBX_cursor *mc) {
  MDBX_page *mp = mc->mc_pg[mc->mc_top];
  MDBX_node *node = NODEPTR(mp, 0);
  int rc;

  if (unlikely((rc = mdbx_page_get(mc, NODEPGNO(node), &mp, NULL)) != 0))
    return rc;

  mc->mc_ki[mc->mc_top] = 0;
  if (unlikely(rc = mdbx_cursor_push(mc, mp)))
    return rc;
  return mdbx_page_search_root(mc, NULL, MDBX_PS_FIRST);
}

/* Search for the page a given key should be in.
 * Push it and its parent pages on the cursor stack.
 *
 * [in,out] mc  the cursor for this operation.
 * [in] key     the key to search for, or NULL for first/last page.
 * [in] flags   If MDBX_PS_MODIFY is set, visited pages in the DB
 *              are touched (updated with new page numbers).
 *              If MDBX_PS_FIRST or MDBX_PS_LAST is set, find first or last
 * leaf.
 *              This is used by mdbx_cursor_first() and mdbx_cursor_last().
 *              If MDBX_PS_ROOTONLY set, just fetch root node, no further
 *              lookups.
 *
 * Returns 0 on success, non-zero on failure. */
static int mdbx_page_search(MDBX_cursor *mc, MDBX_val *key, int flags) {
  int rc;
  pgno_t root;

  /* Make sure the txn is still viable, then find the root from
   * the txn's db table and set it as the root of the cursor's stack. */
  if (unlikely(mc->mc_txn->mt_flags & MDBX_TXN_BLOCKED)) {
    mdbx_debug("transaction has failed, must abort");
    return MDBX_BAD_TXN;
  }

  mdbx_cassert(mc, mc->mc_txn->mt_txnid >= mc->mc_txn->mt_env->me_oldest[0]);
  /* Make sure we're using an up-to-date root */
  if (unlikely(*mc->mc_dbflag & DB_STALE)) {
    MDBX_cursor mc2;
    if (unlikely(TXN_DBI_CHANGED(mc->mc_txn, mc->mc_dbi)))
      return MDBX_BAD_DBI;
    mdbx_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, NULL);
    rc = mdbx_page_search(&mc2, &mc->mc_dbx->md_name, 0);
    if (rc)
      return rc;
    {
      MDBX_val data;
      int exact = 0;
      MDBX_node *leaf = mdbx_node_search(&mc2, &mc->mc_dbx->md_name, &exact);
      if (!exact)
        return MDBX_NOTFOUND;
      if (unlikely((leaf->mn_flags & (F_DUPDATA | F_SUBDATA)) != F_SUBDATA))
        return MDBX_INCOMPATIBLE; /* not a named DB */
      rc = mdbx_node_read(&mc2, leaf, &data);
      if (rc)
        return rc;

      uint16_t md_flags;
      memcpy(&md_flags, ((char *)data.iov_base + offsetof(MDBX_db, md_flags)),
             sizeof(uint16_t));
      /* The txn may not know this DBI, or another process may
       * have dropped and recreated the DB with other flags. */
      if (unlikely((mc->mc_db->md_flags & PERSISTENT_FLAGS) != md_flags))
        return MDBX_INCOMPATIBLE;
      memcpy(mc->mc_db, data.iov_base, sizeof(MDBX_db));
    }
    *mc->mc_dbflag &= ~DB_STALE;
  }
  root = mc->mc_db->md_root;

  if (unlikely(root == P_INVALID)) { /* Tree is empty. */
    mdbx_debug("tree is empty");
    return MDBX_NOTFOUND;
  }

  mdbx_cassert(mc, mc->mc_txn->mt_txnid >= mc->mc_txn->mt_env->me_oldest[0]);
  mdbx_cassert(mc, root >= NUM_METAS);
  if (!mc->mc_pg[0] || mc->mc_pg[0]->mp_pgno != root)
    if (unlikely((rc = mdbx_page_get(mc, root, &mc->mc_pg[0], NULL)) != 0))
      return rc;

  mc->mc_snum = 1;
  mc->mc_top = 0;

  mdbx_debug("db %d root page %" PRIaPGNO " has flags 0x%X", DDBI(mc), root,
             mc->mc_pg[0]->mp_flags);

  if (flags & MDBX_PS_MODIFY) {
    if (unlikely(rc = mdbx_page_touch(mc)))
      return rc;
  }

  if (flags & MDBX_PS_ROOTONLY)
    return MDBX_SUCCESS;

  return mdbx_page_search_root(mc, key, flags);
}

static int mdbx_ovpage_free(MDBX_cursor *mc, MDBX_page *mp) {
  MDBX_txn *txn = mc->mc_txn;
  pgno_t pg = mp->mp_pgno;
  unsigned x = 0, ovpages = mp->mp_pages;
  MDBX_env *env = txn->mt_env;
  MDBX_PNL sl = txn->mt_spill_pages;
  pgno_t pn = pg << 1;
  int rc;

  mdbx_debug("free ov page %" PRIaPGNO " (%u)", pg, ovpages);
  /* If the page is dirty or on the spill list we just acquired it,
   * so we should give it back to our current free list, if any.
   * Otherwise put it onto the list of pages we freed in this txn.
   *
   * Won't create me_reclaimed_pglist: me_last_reclaimed must be inited along
   * with it.
   * Unsupported in nested txns: They would need to hide the page
   * range in ancestor txns' dirty and spilled lists. */
  if (env->me_reclaimed_pglist && !txn->mt_parent &&
      ((mp->mp_flags & P_DIRTY) ||
       (sl && (x = mdbx_pnl_search(sl, pn)) <= sl[0] && sl[x] == pn))) {
    unsigned i, j;
    pgno_t *mop;
    MDBX_ID2 *dl, ix, iy;
    rc = mdbx_pnl_need(&env->me_reclaimed_pglist, ovpages);
    if (unlikely(rc))
      return rc;
    if (!(mp->mp_flags & P_DIRTY)) {
      /* This page is no longer spilled */
      if (x == sl[0])
        sl[0]--;
      else
        sl[x] |= 1;
      goto release;
    }
    /* Remove from dirty list */
    dl = txn->mt_rw_dirtylist;
    x = dl[0].mid--;
    for (ix = dl[x]; ix.mptr != mp; ix = iy) {
      if (likely(x > 1)) {
        x--;
        iy = dl[x];
        dl[x] = ix;
      } else {
        mdbx_cassert(mc, x > 1);
        mdbx_error("not found page 0x%p #%" PRIaPGNO " in the dirtylist", mp,
                   mp->mp_pgno);
        j = ++(dl[0].mid);
        dl[j] = ix; /* Unsorted. OK when MDBX_TXN_ERROR. */
        txn->mt_flags |= MDBX_TXN_ERROR;
        return MDBX_PROBLEM;
      }
    }
    txn->mt_dirtyroom++;
    if (!(env->me_flags & MDBX_WRITEMAP))
      mdbx_dpage_free(env, mp);
  release:
    /* Insert in me_reclaimed_pglist */
    mop = env->me_reclaimed_pglist;
    j = mop[0] + ovpages;
    for (i = mop[0]; i && mop[i] < pg; i--)
      mop[j--] = mop[i];
    while (j > i)
      mop[j--] = pg++;
    mop[0] += ovpages;
  } else {
    rc = mdbx_pnl_append_range(&txn->mt_befree_pages, pg, ovpages);
    if (unlikely(rc))
      return rc;
  }
  mc->mc_db->md_overflow_pages -= ovpages;
  return 0;
}

/* Return the data associated with a given node.
 *
 * [in] mc      The cursor for this operation.
 * [in] leaf    The node being read.
 * [out] data   Updated to point to the node's data.
 *
 * Returns 0 on success, non-zero on failure. */
static __inline int mdbx_node_read(MDBX_cursor *mc, MDBX_node *leaf,
                                   MDBX_val *data) {
  MDBX_page *omp; /* overflow page */
  pgno_t pgno;
  int rc;

  mdbx_cassert(mc, mc->mc_txn->mt_txnid >= mc->mc_txn->mt_env->me_oldest[0]);
  if (!F_ISSET(leaf->mn_flags, F_BIGDATA)) {
    data->iov_len = NODEDSZ(leaf);
    data->iov_base = NODEDATA(leaf);
    return MDBX_SUCCESS;
  }

  /* Read overflow data. */
  data->iov_len = NODEDSZ(leaf);
  memcpy(&pgno, NODEDATA(leaf), sizeof(pgno));
  if (unlikely((rc = mdbx_page_get(mc, pgno, &omp, NULL)) != 0)) {
    mdbx_debug("read overflow page %" PRIaPGNO " failed", pgno);
    return rc;
  }
  data->iov_base = PAGEDATA(omp);

  return MDBX_SUCCESS;
}

int mdbx_get(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data) {
  MDBX_cursor mc;
  MDBX_xcursor mx;
  int exact = 0;
  DKBUF;

  mdbx_debug("===> get db %u key [%s]", dbi, DKEY(key));

  if (unlikely(!key || !data || !txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_USRVALID)))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_flags & MDBX_TXN_BLOCKED))
    return MDBX_BAD_TXN;

  mdbx_cursor_init(&mc, txn, dbi, &mx);
  return mdbx_cursor_set(&mc, key, data, MDBX_SET, &exact);
}

/* Find a sibling for a page.
 * Replaces the page at the top of the cursor's stack with the specified
 * sibling, if one exists.
 *
 * [in] mc          The cursor for this operation.
 * [in] move_right  Non-zero if the right sibling is requested,
 *                  otherwise the left sibling.
 *
 * Returns 0 on success, non-zero on failure. */
static int mdbx_cursor_sibling(MDBX_cursor *mc, int move_right) {
  int rc;
  MDBX_node *indx;
  MDBX_page *mp;

  mdbx_cassert(mc, mc->mc_txn->mt_txnid >= mc->mc_txn->mt_env->me_oldest[0]);
  if (unlikely(mc->mc_snum < 2)) {
    return MDBX_NOTFOUND; /* root has no siblings */
  }

  mdbx_cursor_pop(mc);
  mdbx_debug("parent page is page %" PRIaPGNO ", index %u",
             mc->mc_pg[mc->mc_top]->mp_pgno, mc->mc_ki[mc->mc_top]);

  if (move_right
          ? (mc->mc_ki[mc->mc_top] + 1u >= NUMKEYS(mc->mc_pg[mc->mc_top]))
          : (mc->mc_ki[mc->mc_top] == 0)) {
    mdbx_debug("no more keys left, moving to %s sibling",
               move_right ? "right" : "left");
    if (unlikely((rc = mdbx_cursor_sibling(mc, move_right)) != MDBX_SUCCESS)) {
      /* undo cursor_pop before returning */
      mc->mc_top++;
      mc->mc_snum++;
      return rc;
    }
  } else {
    if (move_right)
      mc->mc_ki[mc->mc_top]++;
    else
      mc->mc_ki[mc->mc_top]--;
    mdbx_debug("just moving to %s index key %u", move_right ? "right" : "left",
               mc->mc_ki[mc->mc_top]);
  }
  mdbx_cassert(mc, IS_BRANCH(mc->mc_pg[mc->mc_top]));

  indx = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
  if (unlikely((rc = mdbx_page_get(mc, NODEPGNO(indx), &mp, NULL)) != 0)) {
    /* mc will be inconsistent if caller does mc_snum++ as above */
    mc->mc_flags &= ~(C_INITIALIZED | C_EOF);
    return rc;
  }

  mdbx_cursor_push(mc, mp);
  if (!move_right)
    mc->mc_ki[mc->mc_top] = NUMKEYS(mp) - 1;

  return MDBX_SUCCESS;
}

/* Move the cursor to the next data item. */
static int mdbx_cursor_next(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                            MDBX_cursor_op op) {
  MDBX_page *mp;
  MDBX_node *leaf;
  int rc;

  if ((mc->mc_flags & C_DEL) && op == MDBX_NEXT_DUP)
    return MDBX_NOTFOUND;

  if (!(mc->mc_flags & C_INITIALIZED))
    return mdbx_cursor_first(mc, key, data);

  mp = mc->mc_pg[mc->mc_top];
  if (mc->mc_flags & C_EOF) {
    if (mc->mc_ki[mc->mc_top] + 1u >= NUMKEYS(mp))
      return MDBX_NOTFOUND;
    mc->mc_flags ^= C_EOF;
  }

  if (mc->mc_db->md_flags & MDBX_DUPSORT) {
    leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
    if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
      if (op == MDBX_NEXT || op == MDBX_NEXT_DUP) {
        rc =
            mdbx_cursor_next(&mc->mc_xcursor->mx_cursor, data, NULL, MDBX_NEXT);
        if (op != MDBX_NEXT || rc != MDBX_NOTFOUND) {
          if (likely(rc == MDBX_SUCCESS))
            MDBX_GET_KEY(leaf, key);
          return rc;
        }
      }
    } else {
      mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED | C_EOF);
      if (op == MDBX_NEXT_DUP)
        return MDBX_NOTFOUND;
    }
  }

  mdbx_debug("cursor_next: top page is %" PRIaPGNO " in cursor %p", mp->mp_pgno,
             (void *)mc);
  if (mc->mc_flags & C_DEL) {
    mc->mc_flags ^= C_DEL;
    goto skip;
  }

  if (mc->mc_ki[mc->mc_top] + 1u >= NUMKEYS(mp)) {
    mdbx_debug("=====> move to next sibling page");
    if (unlikely((rc = mdbx_cursor_sibling(mc, 1)) != MDBX_SUCCESS)) {
      mc->mc_flags |= C_EOF;
      return rc;
    }
    mp = mc->mc_pg[mc->mc_top];
    mdbx_debug("next page is %" PRIaPGNO ", key index %u", mp->mp_pgno,
               mc->mc_ki[mc->mc_top]);
  } else
    mc->mc_ki[mc->mc_top]++;

skip:
  mdbx_debug("==> cursor points to page %" PRIaPGNO
             " with %u keys, key index %u",
             mp->mp_pgno, NUMKEYS(mp), mc->mc_ki[mc->mc_top]);

  if (IS_LEAF2(mp)) {
    key->iov_len = mc->mc_db->md_xsize;
    key->iov_base = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->iov_len);
    return MDBX_SUCCESS;
  }

  mdbx_cassert(mc, IS_LEAF(mp));
  leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);

  if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
    mdbx_xcursor_init1(mc, leaf);
  }
  if (data) {
    if (unlikely((rc = mdbx_node_read(mc, leaf, data)) != MDBX_SUCCESS))
      return rc;

    if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
      rc = mdbx_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
  }

  MDBX_GET_KEY(leaf, key);
  return MDBX_SUCCESS;
}

/* Move the cursor to the previous data item. */
static int mdbx_cursor_prev(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                            MDBX_cursor_op op) {
  MDBX_page *mp;
  MDBX_node *leaf;
  int rc;

  if ((mc->mc_flags & C_DEL) && op == MDBX_PREV_DUP)
    return MDBX_NOTFOUND;

  if (!(mc->mc_flags & C_INITIALIZED)) {
    rc = mdbx_cursor_last(mc, key, data);
    if (unlikely(rc))
      return rc;
    mc->mc_ki[mc->mc_top]++;
  }

  mp = mc->mc_pg[mc->mc_top];
  if ((mc->mc_db->md_flags & MDBX_DUPSORT) &&
      mc->mc_ki[mc->mc_top] < NUMKEYS(mp)) {
    leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
    if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
      if (op == MDBX_PREV || op == MDBX_PREV_DUP) {
        rc =
            mdbx_cursor_prev(&mc->mc_xcursor->mx_cursor, data, NULL, MDBX_PREV);
        if (op != MDBX_PREV || rc != MDBX_NOTFOUND) {
          if (likely(rc == MDBX_SUCCESS)) {
            MDBX_GET_KEY(leaf, key);
            mc->mc_flags &= ~C_EOF;
          }
          return rc;
        }
      }
    } else {
      mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED | C_EOF);
      if (op == MDBX_PREV_DUP)
        return MDBX_NOTFOUND;
    }
  }

  mdbx_debug("cursor_prev: top page is %" PRIaPGNO " in cursor %p", mp->mp_pgno,
             (void *)mc);

  mc->mc_flags &= ~(C_EOF | C_DEL);

  if (mc->mc_ki[mc->mc_top] == 0) {
    mdbx_debug("=====> move to prev sibling page");
    if ((rc = mdbx_cursor_sibling(mc, 0)) != MDBX_SUCCESS) {
      return rc;
    }
    mp = mc->mc_pg[mc->mc_top];
    mc->mc_ki[mc->mc_top] = NUMKEYS(mp) - 1;
    mdbx_debug("prev page is %" PRIaPGNO ", key index %u", mp->mp_pgno,
               mc->mc_ki[mc->mc_top]);
  } else
    mc->mc_ki[mc->mc_top]--;

  mdbx_debug("==> cursor points to page %" PRIaPGNO
             " with %u keys, key index %u",
             mp->mp_pgno, NUMKEYS(mp), mc->mc_ki[mc->mc_top]);

  if (IS_LEAF2(mp)) {
    key->iov_len = mc->mc_db->md_xsize;
    key->iov_base = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->iov_len);
    return MDBX_SUCCESS;
  }

  mdbx_cassert(mc, IS_LEAF(mp));
  leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);

  if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
    mdbx_xcursor_init1(mc, leaf);
  }
  if (data) {
    if (unlikely((rc = mdbx_node_read(mc, leaf, data)) != MDBX_SUCCESS))
      return rc;

    if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
      rc = mdbx_cursor_last(&mc->mc_xcursor->mx_cursor, data, NULL);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
  }

  MDBX_GET_KEY(leaf, key);
  return MDBX_SUCCESS;
}

/* Set the cursor on a specific data item. */
static int mdbx_cursor_set(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                           MDBX_cursor_op op, int *exactp) {
  int rc;
  MDBX_page *mp;
  MDBX_node *leaf = NULL;
  DKBUF;

  mdbx_cassert(mc, mc->mc_txn->mt_txnid >= mc->mc_txn->mt_env->me_oldest[0]);
  if ((mc->mc_db->md_flags & MDBX_INTEGERKEY) &&
      unlikely(key->iov_len != sizeof(uint32_t) &&
               key->iov_len != sizeof(uint64_t))) {
    mdbx_cassert(mc, !"key-size is invalid for MDBX_INTEGERKEY");
    return MDBX_BAD_VALSIZE;
  }

  if (mc->mc_xcursor)
    mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED | C_EOF);

  /* See if we're already on the right page */
  if (mc->mc_flags & C_INITIALIZED) {
    MDBX_val nodekey;

    mp = mc->mc_pg[mc->mc_top];
    if (!NUMKEYS(mp)) {
      mc->mc_ki[mc->mc_top] = 0;
      return MDBX_NOTFOUND;
    }
    if (mp->mp_flags & P_LEAF2) {
      nodekey.iov_len = mc->mc_db->md_xsize;
      nodekey.iov_base = LEAF2KEY(mp, 0, nodekey.iov_len);
    } else {
      leaf = NODEPTR(mp, 0);
      MDBX_GET_KEY2(leaf, nodekey);
    }
    rc = mc->mc_dbx->md_cmp(key, &nodekey);
    if (rc == 0) {
      /* Probably happens rarely, but first node on the page
       * was the one we wanted.
       */
      mc->mc_ki[mc->mc_top] = 0;
      if (exactp)
        *exactp = 1;
      goto set1;
    }
    if (rc > 0) {
      unsigned i;
      unsigned nkeys = NUMKEYS(mp);
      if (nkeys > 1) {
        if (mp->mp_flags & P_LEAF2) {
          nodekey.iov_base = LEAF2KEY(mp, nkeys - 1, nodekey.iov_len);
        } else {
          leaf = NODEPTR(mp, nkeys - 1);
          MDBX_GET_KEY2(leaf, nodekey);
        }
        rc = mc->mc_dbx->md_cmp(key, &nodekey);
        if (rc == 0) {
          /* last node was the one we wanted */
          mdbx_cassert(mc, nkeys >= 1 && nkeys <= UINT16_MAX + 1);
          mc->mc_ki[mc->mc_top] = (indx_t)(nkeys - 1);
          if (exactp)
            *exactp = 1;
          goto set1;
        }
        if (rc < 0) {
          if (mc->mc_ki[mc->mc_top] < NUMKEYS(mp)) {
            /* This is definitely the right page, skip search_page */
            if (mp->mp_flags & P_LEAF2) {
              nodekey.iov_base =
                  LEAF2KEY(mp, mc->mc_ki[mc->mc_top], nodekey.iov_len);
            } else {
              leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
              MDBX_GET_KEY2(leaf, nodekey);
            }
            rc = mc->mc_dbx->md_cmp(key, &nodekey);
            if (rc == 0) {
              /* current node was the one we wanted */
              if (exactp)
                *exactp = 1;
              goto set1;
            }
          }
          rc = 0;
          mc->mc_flags &= ~C_EOF;
          goto set2;
        }
      }
      /* If any parents have right-sibs, search.
       * Otherwise, there's nothing further. */
      for (i = 0; i < mc->mc_top; i++)
        if (mc->mc_ki[i] < NUMKEYS(mc->mc_pg[i]) - 1)
          break;
      if (i == mc->mc_top) {
        /* There are no other pages */
        mdbx_cassert(mc, nkeys <= UINT16_MAX);
        mc->mc_ki[mc->mc_top] = (uint16_t)nkeys;
        return MDBX_NOTFOUND;
      }
    }
    if (!mc->mc_top) {
      /* There are no other pages */
      mc->mc_ki[mc->mc_top] = 0;
      if (op == MDBX_SET_RANGE && !exactp) {
        rc = 0;
        goto set1;
      } else
        return MDBX_NOTFOUND;
    }
  } else {
    mc->mc_pg[0] = 0;
  }

  rc = mdbx_page_search(mc, key, 0);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;

  mp = mc->mc_pg[mc->mc_top];
  mdbx_cassert(mc, IS_LEAF(mp));

set2:
  leaf = mdbx_node_search(mc, key, exactp);
  if (exactp != NULL && !*exactp) {
    /* MDBX_SET specified and not an exact match. */
    return MDBX_NOTFOUND;
  }

  if (leaf == NULL) {
    mdbx_debug("===> inexact leaf not found, goto sibling");
    if (unlikely((rc = mdbx_cursor_sibling(mc, 1)) != MDBX_SUCCESS)) {
      mc->mc_flags |= C_EOF;
      return rc; /* no entries matched */
    }
    mp = mc->mc_pg[mc->mc_top];
    mdbx_cassert(mc, IS_LEAF(mp));
    leaf = NODEPTR(mp, 0);
  }

set1:
  mc->mc_flags |= C_INITIALIZED;
  mc->mc_flags &= ~C_EOF;

  if (IS_LEAF2(mp)) {
    if (op == MDBX_SET_RANGE || op == MDBX_SET_KEY) {
      key->iov_len = mc->mc_db->md_xsize;
      key->iov_base = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->iov_len);
    }
    return MDBX_SUCCESS;
  }

  if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
    mdbx_xcursor_init1(mc, leaf);
  }
  if (likely(data)) {
    if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
      if (op == MDBX_SET || op == MDBX_SET_KEY || op == MDBX_SET_RANGE) {
        rc = mdbx_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
      } else {
        int ex2, *ex2p;
        if (op == MDBX_GET_BOTH) {
          ex2p = &ex2;
          ex2 = 0;
        } else {
          ex2p = NULL;
        }
        rc = mdbx_cursor_set(&mc->mc_xcursor->mx_cursor, data, NULL,
                             MDBX_SET_RANGE, ex2p);
        if (unlikely(rc != MDBX_SUCCESS))
          return rc;
      }
    } else if (op == MDBX_GET_BOTH || op == MDBX_GET_BOTH_RANGE) {
      MDBX_val olddata;
      if (unlikely((rc = mdbx_node_read(mc, leaf, &olddata)) != MDBX_SUCCESS))
        return rc;
      rc = mc->mc_dbx->md_dcmp(data, &olddata);
      if (rc) {
        if (op == MDBX_GET_BOTH || rc > 0)
          return MDBX_NOTFOUND;
        rc = 0;
      }
      *data = olddata;
    } else {
      if (mc->mc_xcursor)
        mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED | C_EOF);
      if (unlikely((rc = mdbx_node_read(mc, leaf, data)) != MDBX_SUCCESS))
        return rc;
    }
  }

  /* The key already matches in all other cases */
  if (op == MDBX_SET_RANGE || op == MDBX_SET_KEY)
    MDBX_GET_KEY(leaf, key);

  mdbx_debug("==> cursor placed on key [%s], data [%s]", DKEY(key), DVAL(data));
  return rc;
}

/* Move the cursor to the first item in the database. */
static int mdbx_cursor_first(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data) {
  int rc;
  MDBX_node *leaf;

  if (mc->mc_xcursor)
    mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED | C_EOF);

  if (!(mc->mc_flags & C_INITIALIZED) || mc->mc_top) {
    rc = mdbx_page_search(mc, NULL, MDBX_PS_FIRST);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
  }
  mdbx_cassert(mc, IS_LEAF(mc->mc_pg[mc->mc_top]));

  leaf = NODEPTR(mc->mc_pg[mc->mc_top], 0);
  mc->mc_flags |= C_INITIALIZED;
  mc->mc_flags &= ~C_EOF;

  mc->mc_ki[mc->mc_top] = 0;

  if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
    key->iov_len = mc->mc_db->md_xsize;
    key->iov_base = LEAF2KEY(mc->mc_pg[mc->mc_top], 0, key->iov_len);
    return MDBX_SUCCESS;
  }

  if (likely(data)) {
    if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
      mdbx_cassert(mc, mc->mc_xcursor != nullptr);
      mdbx_xcursor_init1(mc, leaf);
      rc = mdbx_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
      if (unlikely(rc))
        return rc;
    } else {
      if (unlikely((rc = mdbx_node_read(mc, leaf, data)) != MDBX_SUCCESS))
        return rc;
    }
  }
  MDBX_GET_KEY(leaf, key);
  return MDBX_SUCCESS;
}

/* Move the cursor to the last item in the database. */
static int mdbx_cursor_last(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data) {
  int rc;
  MDBX_node *leaf;

  if (mc->mc_xcursor)
    mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED | C_EOF);

  if (likely((mc->mc_flags & (C_EOF | C_DEL)) != C_EOF)) {
    if (!(mc->mc_flags & C_INITIALIZED) || mc->mc_top) {
      rc = mdbx_page_search(mc, NULL, MDBX_PS_LAST);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
    mdbx_cassert(mc, IS_LEAF(mc->mc_pg[mc->mc_top]));
  }

  mc->mc_ki[mc->mc_top] = NUMKEYS(mc->mc_pg[mc->mc_top]) - 1;
  mc->mc_flags |= C_INITIALIZED | C_EOF;
  leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);

  if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
    key->iov_len = mc->mc_db->md_xsize;
    key->iov_base =
        LEAF2KEY(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], key->iov_len);
    return MDBX_SUCCESS;
  }

  if (likely(data)) {
    if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
      mdbx_cassert(mc, mc->mc_xcursor != nullptr);
      mdbx_xcursor_init1(mc, leaf);
      rc = mdbx_cursor_last(&mc->mc_xcursor->mx_cursor, data, NULL);
      if (unlikely(rc))
        return rc;
    } else {
      if (unlikely((rc = mdbx_node_read(mc, leaf, data)) != MDBX_SUCCESS))
        return rc;
    }
  }

  MDBX_GET_KEY(leaf, key);
  return MDBX_SUCCESS;
}

int mdbx_cursor_get(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                    MDBX_cursor_op op) {
  int rc;
  int exact = 0;
  int (*mfunc)(MDBX_cursor * mc, MDBX_val * key, MDBX_val * data);

  if (unlikely(mc == NULL))
    return MDBX_EINVAL;

  if (unlikely(mc->mc_signature != MDBX_MC_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(mc->mc_txn->mt_flags & MDBX_TXN_BLOCKED))
    return MDBX_BAD_TXN;

  mdbx_cassert(mc, mc->mc_txn->mt_txnid >= mc->mc_txn->mt_env->me_oldest[0]);
  switch (op) {
  case MDBX_GET_CURRENT: {
    if (unlikely(!(mc->mc_flags & C_INITIALIZED)))
      return MDBX_EINVAL;
    MDBX_page *mp = mc->mc_pg[mc->mc_top];
    unsigned nkeys = NUMKEYS(mp);
    if (mc->mc_ki[mc->mc_top] >= nkeys) {
      mdbx_cassert(mc, nkeys <= UINT16_MAX);
      mc->mc_ki[mc->mc_top] = (uint16_t)nkeys;
      return MDBX_NOTFOUND;
    }
    assert(nkeys > 0);

    rc = MDBX_SUCCESS;
    if (IS_LEAF2(mp)) {
      key->iov_len = mc->mc_db->md_xsize;
      key->iov_base = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->iov_len);
    } else {
      MDBX_node *leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
      MDBX_GET_KEY(leaf, key);
      if (data) {
        if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
          if (unlikely(!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED))) {
            mdbx_xcursor_init1(mc, leaf);
            rc = mdbx_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
            if (unlikely(rc))
              return rc;
          }
          rc = mdbx_cursor_get(&mc->mc_xcursor->mx_cursor, data, NULL,
                               MDBX_GET_CURRENT);
        } else {
          rc = mdbx_node_read(mc, leaf, data);
        }
        if (unlikely(rc))
          return rc;
      }
    }
    break;
  }
  case MDBX_GET_BOTH:
  case MDBX_GET_BOTH_RANGE:
    if (unlikely(data == NULL))
      return MDBX_EINVAL;
    if (unlikely(mc->mc_xcursor == NULL))
      return MDBX_INCOMPATIBLE;
  /* FALLTHRU */
  case MDBX_SET:
  case MDBX_SET_KEY:
  case MDBX_SET_RANGE:
    if (unlikely(key == NULL))
      return MDBX_EINVAL;
    rc = mdbx_cursor_set(mc, key, data, op,
                         op == MDBX_SET_RANGE ? NULL : &exact);
    break;
  case MDBX_GET_MULTIPLE:
    if (unlikely(data == NULL || !(mc->mc_flags & C_INITIALIZED)))
      return MDBX_EINVAL;
    if (unlikely(!(mc->mc_db->md_flags & MDBX_DUPFIXED)))
      return MDBX_INCOMPATIBLE;
    rc = MDBX_SUCCESS;
    if (!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) ||
        (mc->mc_xcursor->mx_cursor.mc_flags & C_EOF))
      break;
    goto fetchm;
  case MDBX_NEXT_MULTIPLE:
    if (unlikely(data == NULL))
      return MDBX_EINVAL;
    if (unlikely(!(mc->mc_db->md_flags & MDBX_DUPFIXED)))
      return MDBX_INCOMPATIBLE;
    rc = mdbx_cursor_next(mc, key, data, MDBX_NEXT_DUP);
    if (rc == MDBX_SUCCESS) {
      if (mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) {
        MDBX_cursor *mx;
      fetchm:
        mx = &mc->mc_xcursor->mx_cursor;
        data->iov_len = NUMKEYS(mx->mc_pg[mx->mc_top]) * mx->mc_db->md_xsize;
        data->iov_base = PAGEDATA(mx->mc_pg[mx->mc_top]);
        mx->mc_ki[mx->mc_top] = NUMKEYS(mx->mc_pg[mx->mc_top]) - 1;
      } else {
        rc = MDBX_NOTFOUND;
      }
    }
    break;
  case MDBX_PREV_MULTIPLE:
    if (data == NULL)
      return MDBX_EINVAL;
    if (!(mc->mc_db->md_flags & MDBX_DUPFIXED))
      return MDBX_INCOMPATIBLE;
    rc = MDBX_SUCCESS;
    if (!(mc->mc_flags & C_INITIALIZED))
      rc = mdbx_cursor_last(mc, key, data);
    if (rc == MDBX_SUCCESS) {
      MDBX_cursor *mx = &mc->mc_xcursor->mx_cursor;
      if (mx->mc_flags & C_INITIALIZED) {
        rc = mdbx_cursor_sibling(mx, 0);
        if (rc == MDBX_SUCCESS)
          goto fetchm;
      } else {
        rc = MDBX_NOTFOUND;
      }
    }
    break;
  case MDBX_NEXT:
  case MDBX_NEXT_DUP:
  case MDBX_NEXT_NODUP:
    rc = mdbx_cursor_next(mc, key, data, op);
    break;
  case MDBX_PREV:
  case MDBX_PREV_DUP:
  case MDBX_PREV_NODUP:
    rc = mdbx_cursor_prev(mc, key, data, op);
    break;
  case MDBX_FIRST:
    rc = mdbx_cursor_first(mc, key, data);
    break;
  case MDBX_FIRST_DUP:
    mfunc = mdbx_cursor_first;
  mmove:
    if (unlikely(data == NULL || !(mc->mc_flags & C_INITIALIZED)))
      return MDBX_EINVAL;
    if (unlikely(mc->mc_xcursor == NULL))
      return MDBX_INCOMPATIBLE;
    {
      MDBX_node *leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
      if (!F_ISSET(leaf->mn_flags, F_DUPDATA)) {
        MDBX_GET_KEY(leaf, key);
        rc = mdbx_node_read(mc, leaf, data);
        break;
      }
    }
    if (unlikely(!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED)))
      return MDBX_EINVAL;
    rc = mfunc(&mc->mc_xcursor->mx_cursor, data, NULL);
    break;
  case MDBX_LAST:
    rc = mdbx_cursor_last(mc, key, data);
    break;
  case MDBX_LAST_DUP:
    mfunc = mdbx_cursor_last;
    goto mmove;
  default:
    mdbx_debug("unhandled/unimplemented cursor operation %u", op);
    return MDBX_EINVAL;
  }

  mc->mc_flags &= ~C_DEL;
  return rc;
}

/* Touch all the pages in the cursor stack. Set mc_top.
 * Makes sure all the pages are writable, before attempting a write operation.
 * [in] mc The cursor to operate on. */
static int mdbx_cursor_touch(MDBX_cursor *mc) {
  int rc = MDBX_SUCCESS;

  if (mc->mc_dbi >= CORE_DBS && !(*mc->mc_dbflag & (DB_DIRTY | DB_DUPDATA))) {
    /* Touch DB record of named DB */
    MDBX_cursor mc2;
    MDBX_xcursor mcx;
    if (TXN_DBI_CHANGED(mc->mc_txn, mc->mc_dbi))
      return MDBX_BAD_DBI;
    mdbx_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, &mcx);
    rc = mdbx_page_search(&mc2, &mc->mc_dbx->md_name, MDBX_PS_MODIFY);
    if (unlikely(rc))
      return rc;
    *mc->mc_dbflag |= DB_DIRTY;
  }
  mc->mc_top = 0;
  if (mc->mc_snum) {
    do {
      rc = mdbx_page_touch(mc);
    } while (!rc && ++(mc->mc_top) < mc->mc_snum);
    mc->mc_top = mc->mc_snum - 1;
  }
  return rc;
}

/* Do not spill pages to disk if txn is getting full, may fail instead */
#define MDBX_NOSPILL 0x8000

int mdbx_cursor_put(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                    unsigned flags) {
  MDBX_env *env;
  MDBX_page *fp, *sub_root = NULL;
  uint16_t fp_flags;
  MDBX_val xdata, *rdata, dkey, olddata;
  MDBX_db dummy;
  unsigned mcount = 0, dcount = 0, nospill;
  size_t nsize;
  int rc = MDBX_SUCCESS, rc2;
  unsigned nflags;
  DKBUF;

  if (unlikely(mc == NULL || key == NULL))
    return MDBX_EINVAL;

  if (unlikely(mc->mc_signature != MDBX_MC_SIGNATURE))
    return MDBX_EBADSIGN;

  env = mc->mc_txn->mt_env;

  /* Check this first so counter will always be zero on any early failures. */
  if (flags & MDBX_MULTIPLE) {
    if (unlikely(!F_ISSET(mc->mc_db->md_flags, MDBX_DUPFIXED)))
      return MDBX_INCOMPATIBLE;
    if (unlikely(data[1].iov_len >= INT_MAX))
      return MDBX_EINVAL;
    dcount = (unsigned)data[1].iov_len;
    data[1].iov_len = 0;
  }

  if (flags & MDBX_RESERVE) {
    if (unlikely(mc->mc_db->md_flags & (MDBX_DUPSORT | MDBX_REVERSEDUP)))
      return MDBX_INCOMPATIBLE;
    data->iov_base = nullptr;
  }

  nospill = flags & MDBX_NOSPILL;
  flags &= ~MDBX_NOSPILL;

  if (unlikely(mc->mc_txn->mt_flags & (MDBX_TXN_RDONLY | MDBX_TXN_BLOCKED)))
    return (mc->mc_txn->mt_flags & MDBX_TXN_RDONLY) ? MDBX_EACCESS
                                                    : MDBX_BAD_TXN;

  if (unlikely(key->iov_len > env->me_maxkey_limit))
    return MDBX_BAD_VALSIZE;

  if (unlikely(data->iov_len > ((mc->mc_db->md_flags & MDBX_DUPSORT)
                                    ? env->me_maxkey_limit
                                    : MDBX_MAXDATASIZE)))
    return MDBX_BAD_VALSIZE;

  if ((mc->mc_db->md_flags & MDBX_INTEGERKEY) &&
      unlikely(key->iov_len != sizeof(uint32_t) &&
               key->iov_len != sizeof(uint64_t))) {
    mdbx_cassert(mc, !"key-size is invalid for MDBX_INTEGERKEY");
    return MDBX_BAD_VALSIZE;
  }

  if ((mc->mc_db->md_flags & MDBX_INTEGERDUP) &&
      unlikely(data->iov_len != sizeof(uint32_t) &&
               data->iov_len != sizeof(uint64_t))) {
    mdbx_cassert(mc, !"data-size is invalid MDBX_INTEGERDUP");
    return MDBX_BAD_VALSIZE;
  }

  mdbx_debug("==> put db %d key [%s], size %" PRIuPTR
             ", data [%s] size %" PRIuPTR,
             DDBI(mc), DKEY(key), key ? key->iov_len : 0,
             DVAL((flags & MDBX_RESERVE) ? nullptr : data), data->iov_len);

  int dupdata_flag = 0;
  if (flags & MDBX_CURRENT) {
    /* Опция MDBX_CURRENT означает, что запрошено обновление текущей записи,
     * на которой сейчас стоит курсор. Проверяем что переданный ключ совпадает
     * со значением в текущей позиции курсора.
     * Здесь проще вызвать mdbx_cursor_get(), так как для обслуживания таблиц
     * с MDBX_DUPSORT также требуется текущий размер данных. */
    MDBX_val current_key, current_data;
    rc = mdbx_cursor_get(mc, &current_key, &current_data, MDBX_GET_CURRENT);
    if (unlikely(rc != MDBX_SUCCESS))
      return rc;
    if (mc->mc_dbx->md_cmp(key, &current_key) != 0)
      return MDBX_EKEYMISMATCH;

    if (F_ISSET(mc->mc_db->md_flags, MDBX_DUPSORT)) {
      MDBX_node *leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
      if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
        mdbx_cassert(mc,
                     mc->mc_xcursor != NULL &&
                         (mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED));
        /* Если за ключом более одного значения, либо если размер данных
         * отличается, то вместо inplace обновления требуется удаление и
         * последующая вставка. */
        if (mc->mc_xcursor->mx_db.md_entries > 1 ||
            current_data.iov_len != data->iov_len) {
          rc = mdbx_cursor_del(mc, 0);
          if (rc != MDBX_SUCCESS)
            return rc;
          flags -= MDBX_CURRENT;
        }
      }
    }
  }

  if (mc->mc_db->md_root == P_INVALID) {
    /* new database, cursor has nothing to point to */
    mc->mc_snum = 0;
    mc->mc_top = 0;
    mc->mc_flags &= ~C_INITIALIZED;
    rc = MDBX_NO_ROOT;
  } else if ((flags & MDBX_CURRENT) == 0) {
    int exact = 0;
    MDBX_val d2;
    if (flags & MDBX_APPEND) {
      MDBX_val k2;
      rc = mdbx_cursor_last(mc, &k2, &d2);
      if (rc == 0) {
        rc = mc->mc_dbx->md_cmp(key, &k2);
        if (rc > 0) {
          rc = MDBX_NOTFOUND;
          mc->mc_ki[mc->mc_top]++;
        } else {
          /* new key is <= last key */
          rc = MDBX_EKEYMISMATCH;
        }
      }
    } else {
      rc = mdbx_cursor_set(mc, key, &d2, MDBX_SET, &exact);
    }
    if ((flags & MDBX_NOOVERWRITE) && rc == 0) {
      mdbx_debug("duplicate key [%s]", DKEY(key));
      *data = d2;
      return MDBX_KEYEXIST;
    }
    if (rc && unlikely(rc != MDBX_NOTFOUND))
      return rc;
  }

  mc->mc_flags &= ~C_DEL;

  /* Cursor is positioned, check for room in the dirty list */
  if (!nospill) {
    if (flags & MDBX_MULTIPLE) {
      rdata = &xdata;
      xdata.iov_len = data->iov_len * dcount;
    } else {
      rdata = data;
    }
    if (unlikely(rc2 = mdbx_page_spill(mc, key, rdata)))
      return rc2;
  }

  if (rc == MDBX_NO_ROOT) {
    MDBX_page *np;
    /* new database, write a root leaf page */
    mdbx_debug("allocating new root leaf page");
    if (unlikely(rc2 = mdbx_page_new(mc, P_LEAF, 1, &np))) {
      return rc2;
    }
    assert(np->mp_flags & P_LEAF);
    mdbx_cursor_push(mc, np);
    mc->mc_db->md_root = np->mp_pgno;
    mc->mc_db->md_depth++;
    *mc->mc_dbflag |= DB_DIRTY;
    if ((mc->mc_db->md_flags & (MDBX_DUPSORT | MDBX_DUPFIXED)) == MDBX_DUPFIXED)
      np->mp_flags |= P_LEAF2;
    mc->mc_flags |= C_INITIALIZED;
  } else {
    /* make sure all cursor pages are writable */
    rc2 = mdbx_cursor_touch(mc);
    if (unlikely(rc2))
      return rc2;
  }

  bool insert_key, insert_data, do_sub = false;
  insert_key = insert_data = (rc != MDBX_SUCCESS);
  if (insert_key) {
    /* The key does not exist */
    mdbx_debug("inserting key at index %i", mc->mc_ki[mc->mc_top]);
    if ((mc->mc_db->md_flags & MDBX_DUPSORT) &&
        LEAFSIZE(key, data) > env->me_nodemax) {
      /* Too big for a node, insert in sub-DB.  Set up an empty
       * "old sub-page" for prep_subDB to expand to a full page. */
      fp_flags = P_LEAF | P_DIRTY;
      fp = env->me_pbuf;
      fp->mp_leaf2_ksize = (uint16_t)data->iov_len; /* used if MDBX_DUPFIXED */
      fp->mp_lower = fp->mp_upper = 0;
      olddata.iov_len = PAGEHDRSZ;
      goto prep_subDB;
    }
  } else {
    /* there's only a key anyway, so this is a no-op */
    if (IS_LEAF2(mc->mc_pg[mc->mc_top])) {
      char *ptr;
      unsigned ksize = mc->mc_db->md_xsize;
      if (key->iov_len != ksize)
        return MDBX_BAD_VALSIZE;
      ptr = LEAF2KEY(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], ksize);
      memcpy(ptr, key->iov_base, ksize);
    fix_parent:
      /* if overwriting slot 0 of leaf, need to
       * update branch key if there is a parent page */
      if (mc->mc_top && !mc->mc_ki[mc->mc_top]) {
        unsigned dtop = 1;
        mc->mc_top--;
        /* slot 0 is always an empty key, find real slot */
        while (mc->mc_top && !mc->mc_ki[mc->mc_top]) {
          mc->mc_top--;
          dtop++;
        }
        if (mc->mc_ki[mc->mc_top])
          rc2 = mdbx_update_key(mc, key);
        else
          rc2 = MDBX_SUCCESS;
        mdbx_cassert(mc, mc->mc_top + dtop < UINT16_MAX);
        mc->mc_top += (uint16_t)dtop;
        if (rc2)
          return rc2;
      }
      return MDBX_SUCCESS;
    }

  more:;
    MDBX_node *leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
    olddata.iov_len = NODEDSZ(leaf);
    olddata.iov_base = NODEDATA(leaf);

    /* DB has dups? */
    if (F_ISSET(mc->mc_db->md_flags, MDBX_DUPSORT)) {
      /* Prepare (sub-)page/sub-DB to accept the new item, if needed.
       * fp: old sub-page or a header faking it.
       * mp: new (sub-)page.  offset: growth in page size.
       * xdata: node data with new page or DB. */
      unsigned i, offset = 0;
      MDBX_page *mp = fp = xdata.iov_base = env->me_pbuf;
      mp->mp_pgno = mc->mc_pg[mc->mc_top]->mp_pgno;

      /* Was a single item before, must convert now */
      if (!F_ISSET(leaf->mn_flags, F_DUPDATA)) {

        /* does data match? */
        if (!mc->mc_dbx->md_dcmp(data, &olddata)) {
          if (unlikely(flags & (MDBX_NODUPDATA | MDBX_APPENDDUP)))
            return MDBX_KEYEXIST;
          /* overwrite it */
          goto current;
        }

        /* Just overwrite the current item */
        if (flags & MDBX_CURRENT)
          goto current;

        /* Back up original data item */
        dupdata_flag = 1;
        dkey.iov_len = olddata.iov_len;
        dkey.iov_base = memcpy(fp + 1, olddata.iov_base, olddata.iov_len);

        /* Make sub-page header for the dup items, with dummy body */
        fp->mp_flags = P_LEAF | P_DIRTY | P_SUBP;
        fp->mp_lower = 0;
        xdata.iov_len = PAGEHDRSZ + dkey.iov_len + data->iov_len;
        if (mc->mc_db->md_flags & MDBX_DUPFIXED) {
          fp->mp_flags |= P_LEAF2;
          fp->mp_leaf2_ksize = (uint16_t)data->iov_len;
          xdata.iov_len += 2 * data->iov_len; /* leave space for 2 more */
        } else {
          xdata.iov_len += 2 * (sizeof(indx_t) + NODESIZE) +
                           (dkey.iov_len & 1) + (data->iov_len & 1);
        }
        fp->mp_upper = (uint16_t)(xdata.iov_len - PAGEHDRSZ);
        olddata.iov_len = xdata.iov_len; /* pretend olddata is fp */
      } else if (leaf->mn_flags & F_SUBDATA) {
        /* Data is on sub-DB, just store it */
        flags |= F_DUPDATA | F_SUBDATA;
        goto put_sub;
      } else {
        /* Data is on sub-page */
        fp = olddata.iov_base;
        switch (flags) {
        default:
          if (!(mc->mc_db->md_flags & MDBX_DUPFIXED)) {
            offset = EVEN(NODESIZE + sizeof(indx_t) + data->iov_len);
            break;
          }
          offset = fp->mp_leaf2_ksize;
          if (SIZELEFT(fp) < offset) {
            offset *= 4; /* space for 4 more */
            break;
          }
        /* FALLTHRU: Big enough MDBX_DUPFIXED sub-page */
        case MDBX_CURRENT | MDBX_NODUPDATA:
        case MDBX_CURRENT:
          fp->mp_flags |= P_DIRTY;
          fp->mp_pgno = mp->mp_pgno;
          mc->mc_xcursor->mx_cursor.mc_pg[0] = fp;
          flags |= F_DUPDATA;
          goto put_sub;
        }
        xdata.iov_len = olddata.iov_len + offset;
      }

      fp_flags = fp->mp_flags;
      if (NODESIZE + NODEKSZ(leaf) + xdata.iov_len > env->me_nodemax) {
        /* Too big for a sub-page, convert to sub-DB */
        fp_flags &= ~P_SUBP;
      prep_subDB:
        dummy.md_xsize = 0;
        dummy.md_flags = 0;
        if (mc->mc_db->md_flags & MDBX_DUPFIXED) {
          fp_flags |= P_LEAF2;
          dummy.md_xsize = fp->mp_leaf2_ksize;
          dummy.md_flags = MDBX_DUPFIXED;
          if (mc->mc_db->md_flags & MDBX_INTEGERDUP)
            dummy.md_flags |= MDBX_INTEGERKEY;
        }
        dummy.md_depth = 1;
        dummy.md_branch_pages = 0;
        dummy.md_leaf_pages = 1;
        dummy.md_overflow_pages = 0;
        dummy.md_entries = NUMKEYS(fp);
        xdata.iov_len = sizeof(MDBX_db);
        xdata.iov_base = &dummy;
        if ((rc = mdbx_page_alloc(mc, 1, &mp, MDBX_ALLOC_ALL)))
          return rc;
        mdbx_cassert(mc, env->me_psize > olddata.iov_len);
        offset = env->me_psize - (unsigned)olddata.iov_len;
        flags |= F_DUPDATA | F_SUBDATA;
        dummy.md_root = mp->mp_pgno;
        sub_root = mp;
      }
      if (mp != fp) {
        mp->mp_flags = fp_flags | P_DIRTY;
        mp->mp_leaf2_ksize = fp->mp_leaf2_ksize;
        mp->mp_lower = fp->mp_lower;
        mdbx_cassert(mc, fp->mp_upper + offset <= UINT16_MAX);
        mp->mp_upper = (indx_t)(fp->mp_upper + offset);
        if (fp_flags & P_LEAF2) {
          memcpy(PAGEDATA(mp), PAGEDATA(fp), NUMKEYS(fp) * fp->mp_leaf2_ksize);
        } else {
          memcpy((char *)mp + mp->mp_upper + PAGEHDRSZ,
                 (char *)fp + fp->mp_upper + PAGEHDRSZ,
                 olddata.iov_len - fp->mp_upper - PAGEHDRSZ);
          for (i = 0; i < NUMKEYS(fp); i++) {
            mdbx_cassert(mc, fp->mp_ptrs[i] + offset <= UINT16_MAX);
            mp->mp_ptrs[i] = (indx_t)(fp->mp_ptrs[i] + offset);
          }
        }
      }

      rdata = &xdata;
      flags |= F_DUPDATA;
      do_sub = true;
      if (!insert_key)
        mdbx_node_del(mc, 0);
      goto new_sub;
    }
  current:
    /* MDBX passes F_SUBDATA in 'flags' to write a DB record */
    if (unlikely((leaf->mn_flags ^ flags) & F_SUBDATA))
      return MDBX_INCOMPATIBLE;
    /* overflow page overwrites need special handling */
    if (F_ISSET(leaf->mn_flags, F_BIGDATA)) {
      MDBX_page *omp;
      pgno_t pg;
      int level, ovpages, dpages = OVPAGES(env, data->iov_len);

      memcpy(&pg, olddata.iov_base, sizeof(pg));
      if (unlikely((rc2 = mdbx_page_get(mc, pg, &omp, &level)) != 0))
        return rc2;
      ovpages = omp->mp_pages;

      /* Is the ov page large enough? */
      if (ovpages >= dpages) {
        if (!(omp->mp_flags & P_DIRTY) &&
            (level || (env->me_flags & MDBX_WRITEMAP))) {
          rc = mdbx_page_unspill(mc->mc_txn, omp, &omp);
          if (unlikely(rc))
            return rc;
          level = 0; /* dirty in this txn or clean */
        }
        /* Is it dirty? */
        if (omp->mp_flags & P_DIRTY) {
          /* yes, overwrite it. Note in this case we don't
           * bother to try shrinking the page if the new data
           * is smaller than the overflow threshold. */
          if (unlikely(level > 1)) {
            /* It is writable only in a parent txn */
            MDBX_page *np = mdbx_page_malloc(mc->mc_txn, ovpages);
            MDBX_ID2 id2;
            if (unlikely(!np))
              return MDBX_ENOMEM;
            id2.mid = pg;
            id2.mptr = np;
            /* Note - this page is already counted in parent's dirtyroom */
            rc2 = mdbx_mid2l_insert(mc->mc_txn->mt_rw_dirtylist, &id2);
            mdbx_cassert(mc, rc2 == 0);

            /* Currently we make the page look as with put() in the
             * parent txn, in case the user peeks at MDBX_RESERVEd
             * or unused parts. Some users treat ovpages specially. */
            const size_t whole = pgno2bytes(env, ovpages);
            /* Skip the part where MDBX will put *data.
             * Copy end of page, adjusting alignment so
             * compiler may copy words instead of bytes. */
            const size_t off =
                (PAGEHDRSZ + data->iov_len) & -(intptr_t)sizeof(size_t);
            memcpy((size_t *)((char *)np + off), (size_t *)((char *)omp + off),
                   whole - off);
            memcpy(np, omp, PAGEHDRSZ); /* Copy header of page */
            omp = np;
          }
          SETDSZ(leaf, data->iov_len);
          if (F_ISSET(flags, MDBX_RESERVE))
            data->iov_base = PAGEDATA(omp);
          else
            memcpy(PAGEDATA(omp), data->iov_base, data->iov_len);
          return MDBX_SUCCESS;
        }
      }
      if ((rc2 = mdbx_ovpage_free(mc, omp)) != MDBX_SUCCESS)
        return rc2;
    } else if (data->iov_len == olddata.iov_len) {
      assert(EVEN(key->iov_len) == EVEN(leaf->mn_ksize));
      /* same size, just replace it. Note that we could
       * also reuse this node if the new data is smaller,
       * but instead we opt to shrink the node in that case. */
      if (F_ISSET(flags, MDBX_RESERVE))
        data->iov_base = olddata.iov_base;
      else if (!(mc->mc_flags & C_SUB))
        memcpy(olddata.iov_base, data->iov_base, data->iov_len);
      else {
        mdbx_cassert(mc, NUMKEYS(mc->mc_pg[mc->mc_top]) == 1);
        mdbx_cassert(mc, mc->mc_pg[mc->mc_top]->mp_upper ==
                             mc->mc_pg[mc->mc_top]->mp_lower);
        mdbx_cassert(mc, IS_LEAF(mc->mc_pg[mc->mc_top]) &&
                             !IS_LEAF2(mc->mc_pg[mc->mc_top]));
        mdbx_cassert(mc, NODEDSZ(leaf) == 0);
        mdbx_cassert(mc, leaf->mn_flags == 0);
        mdbx_cassert(mc, key->iov_len < UINT16_MAX);
        leaf->mn_ksize = (uint16_t)key->iov_len;
        memcpy(NODEKEY(leaf), key->iov_base, key->iov_len);
        assert((char *)NODEDATA(leaf) + NODEDSZ(leaf) <
               (char *)(mc->mc_pg[mc->mc_top]) + env->me_psize);
        goto fix_parent;
      }
      return MDBX_SUCCESS;
    }
    mdbx_node_del(mc, 0);
  }

  rdata = data;

new_sub:
  nflags = flags & NODE_ADD_FLAGS;
  nsize = IS_LEAF2(mc->mc_pg[mc->mc_top]) ? key->iov_len
                                          : mdbx_leaf_size(env, key, rdata);
  if (SIZELEFT(mc->mc_pg[mc->mc_top]) < nsize) {
    if ((flags & (F_DUPDATA | F_SUBDATA)) == F_DUPDATA)
      nflags &= ~MDBX_APPEND; /* sub-page may need room to grow */
    if (!insert_key)
      nflags |= MDBX_SPLIT_REPLACE;
    rc = mdbx_page_split(mc, key, rdata, P_INVALID, nflags);
  } else {
    /* There is room already in this leaf page. */
    rc = mdbx_node_add(mc, mc->mc_ki[mc->mc_top], key, rdata, 0, nflags);
    if (likely(rc == 0)) {
      /* Adjust other cursors pointing to mp */
      MDBX_cursor *m2, *m3;
      MDBX_dbi dbi = mc->mc_dbi;
      unsigned i = mc->mc_top;
      MDBX_page *mp = mc->mc_pg[i];

      for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2 = m2->mc_next) {
        if (mc->mc_flags & C_SUB)
          m3 = &m2->mc_xcursor->mx_cursor;
        else
          m3 = m2;
        if (m3 == mc || m3->mc_snum < mc->mc_snum || m3->mc_pg[i] != mp)
          continue;
        if (m3->mc_ki[i] >= mc->mc_ki[i] && insert_key) {
          m3->mc_ki[i]++;
        }
        if (XCURSOR_INITED(m3))
          XCURSOR_REFRESH(m3, mp, m3->mc_ki[i]);
      }
    }
  }

  if (likely(rc == MDBX_SUCCESS)) {
    /* Now store the actual data in the child DB. Note that we're
     * storing the user data in the keys field, so there are strict
     * size limits on dupdata. The actual data fields of the child
     * DB are all zero size. */
    if (do_sub) {
      int xflags;
      size_t ecount;
    put_sub:
      xdata.iov_len = 0;
      xdata.iov_base = "";
      MDBX_node *leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
      if (flags & MDBX_CURRENT) {
        xflags = (flags & MDBX_NODUPDATA)
                     ? MDBX_CURRENT | MDBX_NOOVERWRITE | MDBX_NOSPILL
                     : MDBX_CURRENT | MDBX_NOSPILL;
      } else {
        mdbx_xcursor_init1(mc, leaf);
        xflags = (flags & MDBX_NODUPDATA) ? MDBX_NOOVERWRITE | MDBX_NOSPILL
                                          : MDBX_NOSPILL;
      }
      if (sub_root)
        mc->mc_xcursor->mx_cursor.mc_pg[0] = sub_root;
      /* converted, write the original data first */
      if (dupdata_flag) {
        rc = mdbx_cursor_put(&mc->mc_xcursor->mx_cursor, &dkey, &xdata, xflags);
        if (unlikely(rc))
          goto bad_sub;
        /* we've done our job */
        dkey.iov_len = 0;
      }
      if (!(leaf->mn_flags & F_SUBDATA) || sub_root) {
        /* Adjust other cursors pointing to mp */
        MDBX_cursor *m2;
        MDBX_xcursor *mx = mc->mc_xcursor;
        unsigned i = mc->mc_top;
        MDBX_page *mp = mc->mc_pg[i];
        int nkeys = NUMKEYS(mp);

        for (m2 = mc->mc_txn->mt_cursors[mc->mc_dbi]; m2; m2 = m2->mc_next) {
          if (m2 == mc || m2->mc_snum < mc->mc_snum)
            continue;
          if (!(m2->mc_flags & C_INITIALIZED))
            continue;
          if (m2->mc_pg[i] == mp) {
            if (m2->mc_ki[i] == mc->mc_ki[i]) {
              mdbx_xcursor_init2(m2, mx, dupdata_flag);
            } else if (!insert_key && m2->mc_ki[i] < nkeys) {
              XCURSOR_REFRESH(m2, mp, m2->mc_ki[i]);
            }
          }
        }
      }
      mdbx_cassert(mc, mc->mc_xcursor->mx_db.md_entries < SIZE_MAX);
      ecount = (size_t)mc->mc_xcursor->mx_db.md_entries;
      if (flags & MDBX_APPENDDUP)
        xflags |= MDBX_APPEND;
      rc = mdbx_cursor_put(&mc->mc_xcursor->mx_cursor, data, &xdata, xflags);
      if (flags & F_SUBDATA) {
        void *db = NODEDATA(leaf);
        memcpy(db, &mc->mc_xcursor->mx_db, sizeof(MDBX_db));
      }
      insert_data = (ecount != (size_t)mc->mc_xcursor->mx_db.md_entries);
    }
    /* Increment count unless we just replaced an existing item. */
    if (insert_data)
      mc->mc_db->md_entries++;
    if (insert_key) {
      /* Invalidate txn if we created an empty sub-DB */
      if (unlikely(rc))
        goto bad_sub;
      /* If we succeeded and the key didn't exist before,
       * make sure the cursor is marked valid. */
      mc->mc_flags |= C_INITIALIZED;
    }
    if (flags & MDBX_MULTIPLE) {
      if (!rc) {
        mcount++;
        /* let caller know how many succeeded, if any */
        data[1].iov_len = mcount;
        if (mcount < dcount) {
          data[0].iov_base = (char *)data[0].iov_base + data[0].iov_len;
          insert_key = insert_data = false;
          goto more;
        }
      }
    }
    return rc;
  bad_sub:
    if (unlikely(rc == MDBX_KEYEXIST))
      mdbx_error("unexpected %s", "MDBX_KEYEXIST");
    /* should not happen, we deleted that item */
    rc = MDBX_PROBLEM;
  }
  mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
  return rc;
}

int mdbx_cursor_del(MDBX_cursor *mc, unsigned flags) {
  MDBX_node *leaf;
  MDBX_page *mp;
  int rc;

  if (unlikely(!mc))
    return MDBX_EINVAL;

  if (unlikely(mc->mc_signature != MDBX_MC_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(mc->mc_txn->mt_flags & (MDBX_TXN_RDONLY | MDBX_TXN_BLOCKED)))
    return (mc->mc_txn->mt_flags & MDBX_TXN_RDONLY) ? MDBX_EACCESS
                                                    : MDBX_BAD_TXN;

  if (unlikely(!(mc->mc_flags & C_INITIALIZED)))
    return MDBX_EINVAL;

  if (unlikely(mc->mc_ki[mc->mc_top] >= NUMKEYS(mc->mc_pg[mc->mc_top])))
    return MDBX_NOTFOUND;

  if (unlikely(!(flags & MDBX_NOSPILL) &&
               (rc = mdbx_page_spill(mc, NULL, NULL))))
    return rc;

  rc = mdbx_cursor_touch(mc);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;

  mp = mc->mc_pg[mc->mc_top];
  if (IS_LEAF2(mp))
    goto del_key;
  leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);

  if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
    if (flags & MDBX_NODUPDATA) {
      /* mdbx_cursor_del0() will subtract the final entry */
      mc->mc_db->md_entries -= mc->mc_xcursor->mx_db.md_entries - 1;
      mc->mc_xcursor->mx_cursor.mc_flags &= ~C_INITIALIZED;
    } else {
      if (!F_ISSET(leaf->mn_flags, F_SUBDATA)) {
        mc->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
      }
      rc = mdbx_cursor_del(&mc->mc_xcursor->mx_cursor, MDBX_NOSPILL);
      if (unlikely(rc))
        return rc;
      /* If sub-DB still has entries, we're done */
      if (mc->mc_xcursor->mx_db.md_entries) {
        if (leaf->mn_flags & F_SUBDATA) {
          /* update subDB info */
          void *db = NODEDATA(leaf);
          memcpy(db, &mc->mc_xcursor->mx_db, sizeof(MDBX_db));
        } else {
          MDBX_cursor *m2;
          /* shrink fake page */
          mdbx_node_shrink(mp, mc->mc_ki[mc->mc_top]);
          leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
          mc->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
          /* fix other sub-DB cursors pointed at fake pages on this page */
          for (m2 = mc->mc_txn->mt_cursors[mc->mc_dbi]; m2; m2 = m2->mc_next) {
            if (m2 == mc || m2->mc_snum < mc->mc_snum)
              continue;
            if (!(m2->mc_flags & C_INITIALIZED))
              continue;
            if (m2->mc_pg[mc->mc_top] == mp) {
              MDBX_node *n2 = leaf;
              if (m2->mc_ki[mc->mc_top] != mc->mc_ki[mc->mc_top]) {
                n2 = NODEPTR(mp, m2->mc_ki[mc->mc_top]);
                if (n2->mn_flags & F_SUBDATA)
                  continue;
              }
              m2->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(n2);
            }
          }
        }
        mc->mc_db->md_entries--;
        return rc;
      } else {
        mc->mc_xcursor->mx_cursor.mc_flags &= ~C_INITIALIZED;
      }
      /* otherwise fall thru and delete the sub-DB */
    }

    if (leaf->mn_flags & F_SUBDATA) {
      /* add all the child DB's pages to the free list */
      rc = mdbx_drop0(&mc->mc_xcursor->mx_cursor, 0);
      if (unlikely(rc))
        goto fail;
    }
  }
  /* MDBX passes F_SUBDATA in 'flags' to delete a DB record */
  else if (unlikely((leaf->mn_flags ^ flags) & F_SUBDATA)) {
    rc = MDBX_INCOMPATIBLE;
    goto fail;
  }

  /* add overflow pages to free list */
  if (F_ISSET(leaf->mn_flags, F_BIGDATA)) {
    MDBX_page *omp;
    pgno_t pg;

    memcpy(&pg, NODEDATA(leaf), sizeof(pg));
    if (unlikely((rc = mdbx_page_get(mc, pg, &omp, NULL)) ||
                 (rc = mdbx_ovpage_free(mc, omp))))
      goto fail;
  }

del_key:
  return mdbx_cursor_del0(mc);

fail:
  mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
  return rc;
}

/* Allocate and initialize new pages for a database.
 * Set MDBX_TXN_ERROR on failure.
 *
 * [in] mc a  cursor on the database being added to.
 * [in] flags flags defining what type of page is being allocated.
 * [in] num   the number of pages to allocate. This is usually 1,
 *            unless allocating overflow pages for a large record.
 * [out] mp   Address of a page, or NULL on failure.
 *
 * Returns 0 on success, non-zero on failure. */
static int mdbx_page_new(MDBX_cursor *mc, unsigned flags, unsigned num,
                         MDBX_page **mp) {
  MDBX_page *np;
  int rc;

  if (unlikely((rc = mdbx_page_alloc(mc, num, &np, MDBX_ALLOC_ALL))))
    return rc;
  mdbx_debug("allocated new page #%" PRIaPGNO ", size %u", np->mp_pgno,
             mc->mc_txn->mt_env->me_psize);
  np->mp_flags = (uint16_t)(flags | P_DIRTY);
  np->mp_lower = 0;
  np->mp_upper = (indx_t)(mc->mc_txn->mt_env->me_psize - PAGEHDRSZ);

  if (IS_BRANCH(np))
    mc->mc_db->md_branch_pages++;
  else if (IS_LEAF(np))
    mc->mc_db->md_leaf_pages++;
  else if (IS_OVERFLOW(np)) {
    mc->mc_db->md_overflow_pages += num;
    np->mp_pages = num;
  }
  *mp = np;

  return MDBX_SUCCESS;
}

/* Calculate the size of a leaf node.
 *
 * The size depends on the environment's page size; if a data item
 * is too large it will be put onto an overflow page and the node
 * size will only include the key and not the data. Sizes are always
 * rounded up to an even number of bytes, to guarantee 2-byte alignment
 * of the MDBX_node headers.
 *
 * [in] env   The environment handle.
 * [in] key   The key for the node.
 * [in] data  The data for the node.
 *
 * Returns The number of bytes needed to store the node. */
static __inline size_t mdbx_leaf_size(MDBX_env *env, MDBX_val *key,
                                      MDBX_val *data) {
  size_t sz;

  sz = LEAFSIZE(key, data);
  if (sz > env->me_nodemax) {
    /* put on overflow page */
    sz -= data->iov_len - sizeof(pgno_t);
  }

  return EVEN(sz + sizeof(indx_t));
}

/* Calculate the size of a branch node.
 *
 * The size should depend on the environment's page size but since
 * we currently don't support spilling large keys onto overflow
 * pages, it's simply the size of the MDBX_node header plus the
 * size of the key. Sizes are always rounded up to an even number
 * of bytes, to guarantee 2-byte alignment of the MDBX_node headers.
 *
 * [in] env The environment handle.
 * [in] key The key for the node.
 *
 * Returns The number of bytes needed to store the node. */
static __inline size_t mdbx_branch_size(MDBX_env *env, MDBX_val *key) {
  size_t sz;

  sz = INDXSIZE(key);
  if (unlikely(sz > env->me_nodemax)) {
    /* put on overflow page */
    /* not implemented */
    mdbx_assert_fail(env, "INDXSIZE(key) <= env->me_nodemax", __FUNCTION__,
                     __LINE__);
    sz -= key->iov_len - sizeof(pgno_t);
  }

  return sz + sizeof(indx_t);
}

/* Add a node to the page pointed to by the cursor.
 * Set MDBX_TXN_ERROR on failure.
 *
 * [in] mc    The cursor for this operation.
 * [in] indx  The index on the page where the new node should be added.
 * [in] key   The key for the new node.
 * [in] data  The data for the new node, if any.
 * [in] pgno  The page number, if adding a branch node.
 * [in] flags Flags for the node.
 *
 * Returns 0 on success, non-zero on failure. Possible errors are:
 *
 * MDBX_ENOMEM    - failed to allocate overflow pages for the node.
 * MDBX_PAGE_FULL  - there is insufficient room in the page. This error
 *                  should never happen since all callers already calculate
 *                  the page's free space before calling this function. */
static int mdbx_node_add(MDBX_cursor *mc, unsigned indx, MDBX_val *key,
                         MDBX_val *data, pgno_t pgno, unsigned flags) {
  unsigned i;
  size_t node_size = NODESIZE;
  intptr_t room;
  MDBX_node *node;
  MDBX_page *mp = mc->mc_pg[mc->mc_top];
  MDBX_page *ofp = NULL; /* overflow page */
  void *ndata;
  DKBUF;

  mdbx_cassert(mc, mp->mp_upper >= mp->mp_lower);

  mdbx_debug("add to %s %spage %" PRIaPGNO " index %i, data size %" PRIuPTR
             " key size %" PRIuPTR " [%s]",
             IS_LEAF(mp) ? "leaf" : "branch", IS_SUBP(mp) ? "sub-" : "",
             mp->mp_pgno, indx, data ? data->iov_len : 0,
             key ? key->iov_len : 0, DKEY(key));

  if (IS_LEAF2(mp)) {
    mdbx_cassert(mc, key);
    /* Move higher keys up one slot. */
    const int ksize = mc->mc_db->md_xsize;
    char *const ptr = LEAF2KEY(mp, indx, ksize);
    const int diff = NUMKEYS(mp) - indx;
    if (diff > 0)
      memmove(ptr + ksize, ptr, diff * ksize);
    /* insert new key */
    memcpy(ptr, key->iov_base, ksize);

    /* Just using these for counting */
    mdbx_cassert(mc, UINT16_MAX - mp->mp_lower >= (int)sizeof(indx_t));
    mp->mp_lower += sizeof(indx_t);
    mdbx_cassert(mc, mp->mp_upper >= ksize - sizeof(indx_t));
    mp->mp_upper -= (indx_t)(ksize - sizeof(indx_t));
    return MDBX_SUCCESS;
  }

  room = (intptr_t)SIZELEFT(mp) - (intptr_t)sizeof(indx_t);
  if (key != NULL)
    node_size += key->iov_len;
  if (IS_LEAF(mp)) {
    mdbx_cassert(mc, key && data);
    if (unlikely(F_ISSET(flags, F_BIGDATA))) {
      /* Data already on overflow page. */
      node_size += sizeof(pgno_t);
    } else if (unlikely(node_size + data->iov_len >
                        mc->mc_txn->mt_env->me_nodemax)) {
      pgno_t ovpages = OVPAGES(mc->mc_txn->mt_env, data->iov_len);
      int rc;
      /* Put data on overflow page. */
      mdbx_debug("data size is %" PRIuPTR ", node would be %" PRIuPTR
                 ", put data on overflow page",
                 data->iov_len, node_size + data->iov_len);
      node_size = EVEN(node_size + sizeof(pgno_t));
      if ((intptr_t)node_size > room)
        goto full;
      if ((rc = mdbx_page_new(mc, P_OVERFLOW, ovpages, &ofp)))
        return rc;
      mdbx_debug("allocated overflow page %" PRIaPGNO "", ofp->mp_pgno);
      flags |= F_BIGDATA;
      goto update;
    } else {
      node_size += data->iov_len;
    }
  }
  node_size = EVEN(node_size);
  if (unlikely((intptr_t)node_size > room))
    goto full;

update:
  /* Move higher pointers up one slot. */
  for (i = NUMKEYS(mp); i > indx; i--)
    mp->mp_ptrs[i] = mp->mp_ptrs[i - 1];

  /* Adjust free space offsets. */
  size_t ofs = mp->mp_upper - node_size;
  mdbx_cassert(mc, ofs >= mp->mp_lower + sizeof(indx_t));
  mdbx_cassert(mc, ofs <= UINT16_MAX);
  mp->mp_ptrs[indx] = (uint16_t)ofs;
  mp->mp_upper = (uint16_t)ofs;
  mp->mp_lower += sizeof(indx_t);

  /* Write the node data. */
  node = NODEPTR(mp, indx);
  node->mn_ksize = (key == NULL) ? 0 : (uint16_t)key->iov_len;
  node->mn_flags = (uint16_t)flags;
  if (IS_LEAF(mp))
    SETDSZ(node, data->iov_len);
  else
    SETPGNO(node, pgno);

  if (key)
    memcpy(NODEKEY(node), key->iov_base, key->iov_len);

  if (IS_LEAF(mp)) {
    ndata = NODEDATA(node);
    if (unlikely(ofp == NULL)) {
      if (unlikely(F_ISSET(flags, F_BIGDATA)))
        memcpy(ndata, data->iov_base, sizeof(pgno_t));
      else if (F_ISSET(flags, MDBX_RESERVE))
        data->iov_base = ndata;
      else if (likely(ndata != data->iov_base))
        memcpy(ndata, data->iov_base, data->iov_len);
    } else {
      memcpy(ndata, &ofp->mp_pgno, sizeof(pgno_t));
      ndata = PAGEDATA(ofp);
      if (F_ISSET(flags, MDBX_RESERVE))
        data->iov_base = ndata;
      else if (likely(ndata != data->iov_base))
        memcpy(ndata, data->iov_base, data->iov_len);
    }
  }

  return MDBX_SUCCESS;

full:
  mdbx_debug("not enough room in page %" PRIaPGNO ", got %u ptrs", mp->mp_pgno,
             NUMKEYS(mp));
  mdbx_debug("upper-lower = %u - %u = %" PRIiPTR "", mp->mp_upper, mp->mp_lower,
             room);
  mdbx_debug("node size = %" PRIuPTR "", node_size);
  mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
  return MDBX_PAGE_FULL;
}

/* Delete the specified node from a page.
 * [in] mc Cursor pointing to the node to delete.
 * [in] ksize The size of a node. Only used if the page is
 * part of a MDBX_DUPFIXED database. */
static void mdbx_node_del(MDBX_cursor *mc, size_t ksize) {
  MDBX_page *mp = mc->mc_pg[mc->mc_top];
  indx_t indx = mc->mc_ki[mc->mc_top];
  indx_t i, j, numkeys, ptr;
  MDBX_node *node;
  char *base;

  mdbx_debug("delete node %u on %s page %" PRIaPGNO "", indx,
             IS_LEAF(mp) ? "leaf" : "branch", mp->mp_pgno);
  numkeys = NUMKEYS(mp);
  mdbx_cassert(mc, indx < numkeys);

  if (IS_LEAF2(mp)) {
    mdbx_cassert(mc, ksize >= sizeof(indx_t));
    unsigned diff = numkeys - 1 - indx;
    base = LEAF2KEY(mp, indx, ksize);
    if (diff)
      memmove(base, base + ksize, diff * ksize);
    mdbx_cassert(mc, mp->mp_lower >= sizeof(indx_t));
    mp->mp_lower -= sizeof(indx_t);
    mdbx_cassert(mc,
                 (size_t)UINT16_MAX - mp->mp_upper >= ksize - sizeof(indx_t));
    mp->mp_upper += (indx_t)(ksize - sizeof(indx_t));
    return;
  }

  node = NODEPTR(mp, indx);
  size_t sz = NODESIZE + node->mn_ksize;
  if (IS_LEAF(mp)) {
    if (F_ISSET(node->mn_flags, F_BIGDATA))
      sz += sizeof(pgno_t);
    else
      sz += NODEDSZ(node);
  }
  sz = EVEN(sz);

  ptr = mp->mp_ptrs[indx];
  for (i = j = 0; i < numkeys; i++) {
    if (i != indx) {
      mp->mp_ptrs[j] = mp->mp_ptrs[i];
      if (mp->mp_ptrs[i] < ptr) {
        mdbx_cassert(mc, (size_t)UINT16_MAX - mp->mp_ptrs[j] >= sz);
        mp->mp_ptrs[j] += (indx_t)sz;
      }
      j++;
    }
  }

  base = (char *)mp + mp->mp_upper + PAGEHDRSZ;
  memmove(base + sz, base, ptr - mp->mp_upper);

  mdbx_cassert(mc, mp->mp_lower >= sizeof(indx_t));
  mp->mp_lower -= sizeof(indx_t);
  mdbx_cassert(mc, (size_t)UINT16_MAX - mp->mp_upper >= sz);
  mp->mp_upper += (indx_t)sz;
}

/* Compact the main page after deleting a node on a subpage.
 * [in] mp The main page to operate on.
 * [in] indx The index of the subpage on the main page. */
static void mdbx_node_shrink(MDBX_page *mp, unsigned indx) {
  MDBX_node *node;
  MDBX_page *sp, *xp;
  char *base;
  size_t nsize, delta, len, ptr;
  int i;

  node = NODEPTR(mp, indx);
  sp = (MDBX_page *)NODEDATA(node);
  delta = SIZELEFT(sp);
  nsize = NODEDSZ(node) - delta;

  /* Prepare to shift upward, set len = length(subpage part to shift) */
  if (IS_LEAF2(sp)) {
    len = nsize;
    if (nsize & 1)
      return; /* do not make the node uneven-sized */
  } else {
    xp = (MDBX_page *)((char *)sp + delta); /* destination subpage */
    for (i = NUMKEYS(sp); --i >= 0;) {
      assert(sp->mp_ptrs[i] >= delta);
      xp->mp_ptrs[i] = (indx_t)(sp->mp_ptrs[i] - delta);
    }
    len = PAGEHDRSZ;
  }
  sp->mp_upper = sp->mp_lower;
  sp->mp_pgno = mp->mp_pgno;
  SETDSZ(node, nsize);

  /* Shift <lower nodes...initial part of subpage> upward */
  base = (char *)mp + mp->mp_upper + PAGEHDRSZ;
  memmove(base + delta, base, (char *)sp + len - base);

  ptr = mp->mp_ptrs[indx];
  for (i = NUMKEYS(mp); --i >= 0;) {
    if (mp->mp_ptrs[i] <= ptr) {
      assert((size_t)UINT16_MAX - mp->mp_ptrs[i] >= delta);
      mp->mp_ptrs[i] += (indx_t)delta;
    }
  }
  assert((size_t)UINT16_MAX - mp->mp_upper >= delta);
  mp->mp_upper += (indx_t)delta;
}

/* Initial setup of a sorted-dups cursor.
 *
 * Sorted duplicates are implemented as a sub-database for the given key.
 * The duplicate data items are actually keys of the sub-database.
 * Operations on the duplicate data items are performed using a sub-cursor
 * initialized when the sub-database is first accessed. This function does
 * the preliminary setup of the sub-cursor, filling in the fields that
 * depend only on the parent DB.
 *
 * [in] mc The main cursor whose sorted-dups cursor is to be initialized. */
static void mdbx_xcursor_init0(MDBX_cursor *mc) {
  MDBX_xcursor *mx = mc->mc_xcursor;

  mx->mx_cursor.mc_xcursor = NULL;
  mx->mx_cursor.mc_txn = mc->mc_txn;
  mx->mx_cursor.mc_db = &mx->mx_db;
  mx->mx_cursor.mc_dbx = &mx->mx_dbx;
  mx->mx_cursor.mc_dbi = mc->mc_dbi;
  mx->mx_cursor.mc_dbflag = &mx->mx_dbflag;
  mx->mx_cursor.mc_snum = 0;
  mx->mx_cursor.mc_top = 0;
  mx->mx_cursor.mc_flags = C_SUB;
  mx->mx_dbx.md_name.iov_len = 0;
  mx->mx_dbx.md_name.iov_base = NULL;
  mx->mx_dbx.md_cmp = mc->mc_dbx->md_dcmp;
  mx->mx_dbx.md_dcmp = NULL;
}

/* Final setup of a sorted-dups cursor.
 * Sets up the fields that depend on the data from the main cursor.
 * [in] mc The main cursor whose sorted-dups cursor is to be initialized.
 * [in] node The data containing the MDBX_db record for the sorted-dup database.
 */
static void mdbx_xcursor_init1(MDBX_cursor *mc, MDBX_node *node) {
  MDBX_xcursor *mx = mc->mc_xcursor;

  mdbx_cassert(mc, mc->mc_txn->mt_txnid >= mc->mc_txn->mt_env->me_oldest[0]);
  if (node->mn_flags & F_SUBDATA) {
    memcpy(&mx->mx_db, NODEDATA(node), sizeof(MDBX_db));
    mx->mx_cursor.mc_pg[0] = 0;
    mx->mx_cursor.mc_snum = 0;
    mx->mx_cursor.mc_top = 0;
    mx->mx_cursor.mc_flags = C_SUB;
  } else {
    MDBX_page *fp = NODEDATA(node);
    mx->mx_db.md_xsize = 0;
    mx->mx_db.md_flags = 0;
    mx->mx_db.md_depth = 1;
    mx->mx_db.md_branch_pages = 0;
    mx->mx_db.md_leaf_pages = 1;
    mx->mx_db.md_overflow_pages = 0;
    mx->mx_db.md_entries = NUMKEYS(fp);
    mx->mx_db.md_root = fp->mp_pgno;
    mx->mx_cursor.mc_snum = 1;
    mx->mx_cursor.mc_top = 0;
    mx->mx_cursor.mc_flags = C_INITIALIZED | C_SUB;
    mx->mx_cursor.mc_pg[0] = fp;
    mx->mx_cursor.mc_ki[0] = 0;
    if (mc->mc_db->md_flags & MDBX_DUPFIXED) {
      mx->mx_db.md_flags = MDBX_DUPFIXED;
      mx->mx_db.md_xsize = fp->mp_leaf2_ksize;
      if (mc->mc_db->md_flags & MDBX_INTEGERDUP)
        mx->mx_db.md_flags |= MDBX_INTEGERKEY;
    }
  }
  mdbx_debug("Sub-db -%u root page %" PRIaPGNO "", mx->mx_cursor.mc_dbi,
             mx->mx_db.md_root);
  mx->mx_dbflag = DB_VALID | DB_USRVALID | DB_DUPDATA;
  /* FIXME: #if UINT_MAX < SIZE_MAX
          if (mx->mx_dbx.md_cmp == mdbx_cmp_int && mx->mx_db.md_pad ==
  sizeof(size_t))
                  mx->mx_dbx.md_cmp = mdbx_cmp_clong;
  #endif */
}

/* Fixup a sorted-dups cursor due to underlying update.
 * Sets up some fields that depend on the data from the main cursor.
 * Almost the same as init1, but skips initialization steps if the
 * xcursor had already been used.
 * [in] mc The main cursor whose sorted-dups cursor is to be fixed up.
 * [in] src_mx The xcursor of an up-to-date cursor.
 * [in] new_dupdata True if converting from a non-F_DUPDATA item. */
static void mdbx_xcursor_init2(MDBX_cursor *mc, MDBX_xcursor *src_mx,
                               int new_dupdata) {
  MDBX_xcursor *mx = mc->mc_xcursor;

  mdbx_cassert(mc, mc->mc_txn->mt_txnid >= mc->mc_txn->mt_env->me_oldest[0]);
  if (new_dupdata) {
    mx->mx_cursor.mc_snum = 1;
    mx->mx_cursor.mc_top = 0;
    mx->mx_cursor.mc_flags |= C_INITIALIZED;
    mx->mx_cursor.mc_ki[0] = 0;
    mx->mx_dbflag = DB_VALID | DB_USRVALID | DB_DUPDATA;
    mx->mx_dbx.md_cmp = src_mx->mx_dbx.md_cmp;
  } else if (!(mx->mx_cursor.mc_flags & C_INITIALIZED)) {
    return;
  }
  mx->mx_db = src_mx->mx_db;
  mx->mx_cursor.mc_pg[0] = src_mx->mx_cursor.mc_pg[0];
  mdbx_debug("Sub-db -%u root page %" PRIaPGNO "", mx->mx_cursor.mc_dbi,
             mx->mx_db.md_root);
}

/* Initialize a cursor for a given transaction and database. */
static void mdbx_cursor_init(MDBX_cursor *mc, MDBX_txn *txn, MDBX_dbi dbi,
                             MDBX_xcursor *mx) {
  mc->mc_signature = MDBX_MC_SIGNATURE;
  mc->mc_next = NULL;
  mc->mc_backup = NULL;
  mc->mc_dbi = dbi;
  mc->mc_txn = txn;
  mc->mc_db = &txn->mt_dbs[dbi];
  mc->mc_dbx = &txn->mt_dbxs[dbi];
  mc->mc_dbflag = &txn->mt_dbflags[dbi];
  mc->mc_snum = 0;
  mc->mc_top = 0;
  mc->mc_pg[0] = 0;
  mc->mc_flags = 0;
  mc->mc_ki[0] = 0;
  mc->mc_xcursor = NULL;
  if (txn->mt_dbs[dbi].md_flags & MDBX_DUPSORT) {
    mdbx_tassert(txn, mx != NULL);
    mx->mx_cursor.mc_signature = MDBX_MC_SIGNATURE;
    mc->mc_xcursor = mx;
    mdbx_xcursor_init0(mc);
  }
  mdbx_cassert(mc, mc->mc_txn->mt_txnid >= mc->mc_txn->mt_env->me_oldest[0]);
  if (unlikely(*mc->mc_dbflag & DB_STALE)) {
    mdbx_page_search(mc, NULL, MDBX_PS_ROOTONLY);
  }
}

int mdbx_cursor_open(MDBX_txn *txn, MDBX_dbi dbi, MDBX_cursor **ret) {
  MDBX_cursor *mc;
  size_t size = sizeof(MDBX_cursor);

  if (unlikely(!ret || !txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_VALID)))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_flags & MDBX_TXN_BLOCKED))
    return MDBX_BAD_TXN;

  if (unlikely(dbi == FREE_DBI && !F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY)))
    return MDBX_EINVAL;

  if (txn->mt_dbs[dbi].md_flags & MDBX_DUPSORT)
    size += sizeof(MDBX_xcursor);

  if (likely((mc = malloc(size)) != NULL)) {
    mdbx_cursor_init(mc, txn, dbi, (MDBX_xcursor *)(mc + 1));
    if (txn->mt_cursors) {
      mc->mc_next = txn->mt_cursors[dbi];
      txn->mt_cursors[dbi] = mc;
      mc->mc_flags |= C_UNTRACK;
    }
  } else {
    return MDBX_ENOMEM;
  }

  *ret = mc;

  return MDBX_SUCCESS;
}

int mdbx_cursor_renew(MDBX_txn *txn, MDBX_cursor *mc) {
  if (unlikely(!mc || !txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(mc->mc_signature != MDBX_MC_SIGNATURE &&
               mc->mc_signature != MDBX_MC_READY4CLOSE))
    return MDBX_EINVAL;

  if (unlikely(!TXN_DBI_EXIST(txn, mc->mc_dbi, DB_VALID)))
    return MDBX_EINVAL;

  if (unlikely(mc->mc_backup))
    return MDBX_EINVAL;

  if (unlikely((mc->mc_flags & C_UNTRACK) || txn->mt_cursors)) {
    MDBX_cursor **prev = &mc->mc_txn->mt_cursors[mc->mc_dbi];
    while (*prev && *prev != mc)
      prev = &(*prev)->mc_next;
    if (*prev == mc)
      *prev = mc->mc_next;
    mc->mc_signature = MDBX_MC_READY4CLOSE;
  }

  if (unlikely(txn->mt_flags & MDBX_TXN_BLOCKED))
    return MDBX_BAD_TXN;

  mdbx_cursor_init(mc, txn, mc->mc_dbi, mc->mc_xcursor);
  return MDBX_SUCCESS;
}

/* Return the count of duplicate data items for the current key */
int mdbx_cursor_count(MDBX_cursor *mc, size_t *countp) {
  if (unlikely(mc == NULL || countp == NULL))
    return MDBX_EINVAL;

  if (unlikely(mc->mc_signature != MDBX_MC_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(mc->mc_txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(mc->mc_txn->mt_flags & MDBX_TXN_BLOCKED))
    return MDBX_BAD_TXN;

  if (unlikely(!(mc->mc_flags & C_INITIALIZED)))
    return MDBX_EINVAL;

  if (!mc->mc_snum) {
    *countp = 0;
    return MDBX_NOTFOUND;
  }

  MDBX_page *mp = mc->mc_pg[mc->mc_top];
  if ((mc->mc_flags & C_EOF) && mc->mc_ki[mc->mc_top] >= NUMKEYS(mp)) {
    *countp = 0;
    return MDBX_NOTFOUND;
  }

  *countp = 1;
  if (mc->mc_xcursor != NULL) {
    MDBX_node *leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
    if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
      mdbx_cassert(mc, mc->mc_xcursor && (mc->mc_xcursor->mx_cursor.mc_flags &
                                          C_INITIALIZED));
      *countp = unlikely(mc->mc_xcursor->mx_db.md_entries > SIZE_MAX)
                    ? SIZE_MAX
                    : (size_t)mc->mc_xcursor->mx_db.md_entries;
    }
  }
  return MDBX_SUCCESS;
}

void mdbx_cursor_close(MDBX_cursor *mc) {
  if (mc) {
    mdbx_ensure(NULL, mc->mc_signature == MDBX_MC_SIGNATURE ||
                          mc->mc_signature == MDBX_MC_READY4CLOSE);
    if (!mc->mc_backup) {
      /* Remove from txn, if tracked.
       * A read-only txn (!C_UNTRACK) may have been freed already,
       * so do not peek inside it.  Only write txns track cursors. */
      if ((mc->mc_flags & C_UNTRACK) && mc->mc_txn->mt_cursors) {
        MDBX_cursor **prev = &mc->mc_txn->mt_cursors[mc->mc_dbi];
        while (*prev && *prev != mc)
          prev = &(*prev)->mc_next;
        if (*prev == mc)
          *prev = mc->mc_next;
      }
      mc->mc_signature = 0;
      free(mc);
    } else {
      /* cursor closed before nested txn ends */
      mdbx_cassert(mc, mc->mc_signature == MDBX_MC_SIGNATURE);
      mc->mc_signature = MDBX_MC_WAIT4EOT;
    }
  }
}

MDBX_txn *mdbx_cursor_txn(MDBX_cursor *mc) {
  if (unlikely(!mc || mc->mc_signature != MDBX_MC_SIGNATURE))
    return NULL;
  return mc->mc_txn;
}

MDBX_dbi mdbx_cursor_dbi(MDBX_cursor *mc) {
  if (unlikely(!mc || mc->mc_signature != MDBX_MC_SIGNATURE))
    return UINT_MAX;
  return mc->mc_dbi;
}

/* Replace the key for a branch node with a new key.
 * Set MDBX_TXN_ERROR on failure.
 * [in] mc Cursor pointing to the node to operate on.
 * [in] key The new key to use.
 * Returns 0 on success, non-zero on failure. */
static int mdbx_update_key(MDBX_cursor *mc, MDBX_val *key) {
  MDBX_page *mp;
  MDBX_node *node;
  char *base;
  size_t len;
  int delta, ksize, oksize;
  indx_t ptr, i, numkeys, indx;
  DKBUF;

  indx = mc->mc_ki[mc->mc_top];
  mp = mc->mc_pg[mc->mc_top];
  node = NODEPTR(mp, indx);
  ptr = mp->mp_ptrs[indx];
  if (MDBX_DEBUG) {
    MDBX_val k2;
    char kbuf2[DKBUF_MAXKEYSIZE * 2 + 1];
    k2.iov_base = NODEKEY(node);
    k2.iov_len = node->mn_ksize;
    mdbx_debug("update key %u (ofs %u) [%s] to [%s] on page %" PRIaPGNO "",
               indx, ptr, mdbx_dkey(&k2, kbuf2, sizeof(kbuf2)), DKEY(key),
               mp->mp_pgno);
  }

  /* Sizes must be 2-byte aligned. */
  ksize = EVEN(key->iov_len);
  oksize = EVEN(node->mn_ksize);
  delta = ksize - oksize;

  /* Shift node contents if EVEN(key length) changed. */
  if (delta) {
    if (delta > 0 && SIZELEFT(mp) < delta) {
      pgno_t pgno;
      /* not enough space left, do a delete and split */
      mdbx_debug("Not enough room, delta = %d, splitting...", delta);
      pgno = NODEPGNO(node);
      mdbx_node_del(mc, 0);
      return mdbx_page_split(mc, key, NULL, pgno, MDBX_SPLIT_REPLACE);
    }

    numkeys = NUMKEYS(mp);
    for (i = 0; i < numkeys; i++) {
      if (mp->mp_ptrs[i] <= ptr) {
        mdbx_cassert(mc, mp->mp_ptrs[i] >= delta);
        mp->mp_ptrs[i] -= (indx_t)delta;
      }
    }

    base = (char *)mp + mp->mp_upper + PAGEHDRSZ;
    len = ptr - mp->mp_upper + NODESIZE;
    memmove(base - delta, base, len);
    mdbx_cassert(mc, mp->mp_upper >= delta);
    mp->mp_upper -= (indx_t)delta;

    node = NODEPTR(mp, indx);
  }

  /* But even if no shift was needed, update ksize */
  if (node->mn_ksize != key->iov_len)
    node->mn_ksize = (uint16_t)key->iov_len;

  if (key->iov_len)
    memcpy(NODEKEY(node), key->iov_base, key->iov_len);

  return MDBX_SUCCESS;
}

static void mdbx_cursor_copy(const MDBX_cursor *csrc, MDBX_cursor *cdst);

/* Perform act while tracking temporary cursor mn */
#define WITH_CURSOR_TRACKING(mn, act)                                          \
  do {                                                                         \
    MDBX_cursor mc_dummy, *tracked,                                            \
        **tp = &(mn).mc_txn->mt_cursors[mn.mc_dbi];                            \
    if ((mn).mc_flags & C_SUB) {                                               \
      mc_dummy.mc_flags = C_INITIALIZED;                                       \
      mc_dummy.mc_xcursor = (MDBX_xcursor *)&(mn);                             \
      tracked = &mc_dummy;                                                     \
    } else {                                                                   \
      tracked = &(mn);                                                         \
    }                                                                          \
    tracked->mc_next = *tp;                                                    \
    *tp = tracked;                                                             \
    { act; }                                                                   \
    *tp = tracked->mc_next;                                                    \
  } while (0)

/* Move a node from csrc to cdst. */
static int mdbx_node_move(MDBX_cursor *csrc, MDBX_cursor *cdst, int fromleft) {
  MDBX_node *srcnode;
  MDBX_val key, data;
  pgno_t srcpg;
  MDBX_cursor mn;
  int rc;
  unsigned flags;

  DKBUF;

  /* Mark src and dst as dirty. */
  if (unlikely((rc = mdbx_page_touch(csrc)) || (rc = mdbx_page_touch(cdst))))
    return rc;

  if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
    key.iov_len = csrc->mc_db->md_xsize;
    key.iov_base = LEAF2KEY(csrc->mc_pg[csrc->mc_top],
                            csrc->mc_ki[csrc->mc_top], key.iov_len);
    data.iov_len = 0;
    data.iov_base = NULL;
    srcpg = 0;
    flags = 0;
  } else {
    srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], csrc->mc_ki[csrc->mc_top]);
    mdbx_cassert(csrc, !((size_t)srcnode & 1));
    srcpg = NODEPGNO(srcnode);
    flags = srcnode->mn_flags;
    if (csrc->mc_ki[csrc->mc_top] == 0 &&
        IS_BRANCH(csrc->mc_pg[csrc->mc_top])) {
      unsigned snum = csrc->mc_snum;
      MDBX_node *s2;
      /* must find the lowest key below src */
      rc = mdbx_page_search_lowest(csrc);
      if (unlikely(rc))
        return rc;
      if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
        key.iov_len = csrc->mc_db->md_xsize;
        key.iov_base = LEAF2KEY(csrc->mc_pg[csrc->mc_top], 0, key.iov_len);
      } else {
        s2 = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);
        key.iov_len = NODEKSZ(s2);
        key.iov_base = NODEKEY(s2);
      }
      mdbx_cassert(csrc, snum >= 1 && snum <= UINT16_MAX);
      csrc->mc_snum = (uint16_t)snum--;
      csrc->mc_top = (uint16_t)snum;
    } else {
      key.iov_len = NODEKSZ(srcnode);
      key.iov_base = NODEKEY(srcnode);
    }
    data.iov_len = NODEDSZ(srcnode);
    data.iov_base = NODEDATA(srcnode);
  }
  mn.mc_xcursor = NULL;
  if (IS_BRANCH(cdst->mc_pg[cdst->mc_top]) && cdst->mc_ki[cdst->mc_top] == 0) {
    unsigned snum = cdst->mc_snum;
    MDBX_node *s2;
    MDBX_val bkey;
    /* must find the lowest key below dst */
    mdbx_cursor_copy(cdst, &mn);
    rc = mdbx_page_search_lowest(&mn);
    if (unlikely(rc))
      return rc;
    if (IS_LEAF2(mn.mc_pg[mn.mc_top])) {
      bkey.iov_len = mn.mc_db->md_xsize;
      bkey.iov_base = LEAF2KEY(mn.mc_pg[mn.mc_top], 0, bkey.iov_len);
    } else {
      s2 = NODEPTR(mn.mc_pg[mn.mc_top], 0);
      bkey.iov_len = NODEKSZ(s2);
      bkey.iov_base = NODEKEY(s2);
    }
    mdbx_cassert(csrc, snum >= 1 && snum <= UINT16_MAX);
    mn.mc_snum = (uint16_t)snum--;
    mn.mc_top = (uint16_t)snum;
    mn.mc_ki[snum] = 0;
    rc = mdbx_update_key(&mn, &bkey);
    if (unlikely(rc))
      return rc;
  }

  mdbx_debug("moving %s node %u [%s] on page %" PRIaPGNO
             " to node %u on page %" PRIaPGNO "",
             IS_LEAF(csrc->mc_pg[csrc->mc_top]) ? "leaf" : "branch",
             csrc->mc_ki[csrc->mc_top], DKEY(&key),
             csrc->mc_pg[csrc->mc_top]->mp_pgno, cdst->mc_ki[cdst->mc_top],
             cdst->mc_pg[cdst->mc_top]->mp_pgno);

  /* Add the node to the destination page. */
  rc =
      mdbx_node_add(cdst, cdst->mc_ki[cdst->mc_top], &key, &data, srcpg, flags);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;

  /* Delete the node from the source page. */
  mdbx_node_del(csrc, key.iov_len);

  {
    /* Adjust other cursors pointing to mp */
    MDBX_cursor *m2, *m3;
    MDBX_dbi dbi = csrc->mc_dbi;
    MDBX_page *mpd, *mps;

    mps = csrc->mc_pg[csrc->mc_top];
    /* If we're adding on the left, bump others up */
    if (fromleft) {
      mpd = cdst->mc_pg[csrc->mc_top];
      for (m2 = csrc->mc_txn->mt_cursors[dbi]; m2; m2 = m2->mc_next) {
        if (csrc->mc_flags & C_SUB)
          m3 = &m2->mc_xcursor->mx_cursor;
        else
          m3 = m2;
        if (!(m3->mc_flags & C_INITIALIZED) || m3->mc_top < csrc->mc_top)
          continue;
        if (m3 != cdst && m3->mc_pg[csrc->mc_top] == mpd &&
            m3->mc_ki[csrc->mc_top] >= cdst->mc_ki[csrc->mc_top]) {
          m3->mc_ki[csrc->mc_top]++;
        }
        if (m3 != csrc && m3->mc_pg[csrc->mc_top] == mps &&
            m3->mc_ki[csrc->mc_top] == csrc->mc_ki[csrc->mc_top]) {
          m3->mc_pg[csrc->mc_top] = cdst->mc_pg[cdst->mc_top];
          m3->mc_ki[csrc->mc_top] = cdst->mc_ki[cdst->mc_top];
          m3->mc_ki[csrc->mc_top - 1]++;
        }
        if (XCURSOR_INITED(m3) && IS_LEAF(mps))
          XCURSOR_REFRESH(m3, m3->mc_pg[csrc->mc_top], m3->mc_ki[csrc->mc_top]);
      }
    } else
    /* Adding on the right, bump others down */
    {
      for (m2 = csrc->mc_txn->mt_cursors[dbi]; m2; m2 = m2->mc_next) {
        if (csrc->mc_flags & C_SUB)
          m3 = &m2->mc_xcursor->mx_cursor;
        else
          m3 = m2;
        if (m3 == csrc)
          continue;
        if (!(m3->mc_flags & C_INITIALIZED) || m3->mc_top < csrc->mc_top)
          continue;
        if (m3->mc_pg[csrc->mc_top] == mps) {
          if (!m3->mc_ki[csrc->mc_top]) {
            m3->mc_pg[csrc->mc_top] = cdst->mc_pg[cdst->mc_top];
            m3->mc_ki[csrc->mc_top] = cdst->mc_ki[cdst->mc_top];
            m3->mc_ki[csrc->mc_top - 1]--;
          } else {
            m3->mc_ki[csrc->mc_top]--;
          }
          if (XCURSOR_INITED(m3) && IS_LEAF(mps))
            XCURSOR_REFRESH(m3, m3->mc_pg[csrc->mc_top],
                            m3->mc_ki[csrc->mc_top]);
        }
      }
    }
  }

  /* Update the parent separators. */
  if (csrc->mc_ki[csrc->mc_top] == 0) {
    if (csrc->mc_ki[csrc->mc_top - 1] != 0) {
      if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
        key.iov_base = LEAF2KEY(csrc->mc_pg[csrc->mc_top], 0, key.iov_len);
      } else {
        srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);
        key.iov_len = NODEKSZ(srcnode);
        key.iov_base = NODEKEY(srcnode);
      }
      mdbx_debug("update separator for source page %" PRIaPGNO " to [%s]",
                 csrc->mc_pg[csrc->mc_top]->mp_pgno, DKEY(&key));
      mdbx_cursor_copy(csrc, &mn);
      mn.mc_snum--;
      mn.mc_top--;
      /* We want mdbx_rebalance to find mn when doing fixups */
      WITH_CURSOR_TRACKING(mn, rc = mdbx_update_key(&mn, &key));
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
    if (IS_BRANCH(csrc->mc_pg[csrc->mc_top])) {
      MDBX_val nullkey;
      indx_t ix = csrc->mc_ki[csrc->mc_top];
      nullkey.iov_len = 0;
      csrc->mc_ki[csrc->mc_top] = 0;
      rc = mdbx_update_key(csrc, &nullkey);
      csrc->mc_ki[csrc->mc_top] = ix;
      mdbx_cassert(csrc, rc == MDBX_SUCCESS);
    }
  }

  if (cdst->mc_ki[cdst->mc_top] == 0) {
    if (cdst->mc_ki[cdst->mc_top - 1] != 0) {
      if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
        key.iov_base = LEAF2KEY(cdst->mc_pg[cdst->mc_top], 0, key.iov_len);
      } else {
        srcnode = NODEPTR(cdst->mc_pg[cdst->mc_top], 0);
        key.iov_len = NODEKSZ(srcnode);
        key.iov_base = NODEKEY(srcnode);
      }
      mdbx_debug("update separator for destination page %" PRIaPGNO " to [%s]",
                 cdst->mc_pg[cdst->mc_top]->mp_pgno, DKEY(&key));
      mdbx_cursor_copy(cdst, &mn);
      mn.mc_snum--;
      mn.mc_top--;
      /* We want mdbx_rebalance to find mn when doing fixups */
      WITH_CURSOR_TRACKING(mn, rc = mdbx_update_key(&mn, &key));
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
    if (IS_BRANCH(cdst->mc_pg[cdst->mc_top])) {
      MDBX_val nullkey;
      indx_t ix = cdst->mc_ki[cdst->mc_top];
      nullkey.iov_len = 0;
      cdst->mc_ki[cdst->mc_top] = 0;
      rc = mdbx_update_key(cdst, &nullkey);
      cdst->mc_ki[cdst->mc_top] = ix;
      mdbx_cassert(cdst, rc == MDBX_SUCCESS);
    }
  }

  return MDBX_SUCCESS;
}

/* Merge one page into another.
 *
 * The nodes from the page pointed to by csrc will be copied to the page
 * pointed to by cdst and then the csrc page will be freed.
 *
 * [in] csrc Cursor pointing to the source page.
 * [in] cdst Cursor pointing to the destination page.
 *
 * Returns 0 on success, non-zero on failure. */
static int mdbx_page_merge(MDBX_cursor *csrc, MDBX_cursor *cdst) {
  MDBX_page *psrc, *pdst;
  MDBX_node *srcnode;
  MDBX_val key, data;
  unsigned nkeys;
  int rc;
  unsigned i, j;

  psrc = csrc->mc_pg[csrc->mc_top];
  pdst = cdst->mc_pg[cdst->mc_top];

  mdbx_debug("merging page %" PRIaPGNO " into %" PRIaPGNO "", psrc->mp_pgno,
             pdst->mp_pgno);

  mdbx_cassert(csrc, csrc->mc_snum > 1); /* can't merge root page */
  mdbx_cassert(csrc, cdst->mc_snum > 1);

  /* Mark dst as dirty. */
  if (unlikely(rc = mdbx_page_touch(cdst)))
    return rc;

  /* get dst page again now that we've touched it. */
  pdst = cdst->mc_pg[cdst->mc_top];

  /* Move all nodes from src to dst. */
  j = nkeys = NUMKEYS(pdst);
  if (IS_LEAF2(psrc)) {
    key.iov_len = csrc->mc_db->md_xsize;
    key.iov_base = PAGEDATA(psrc);
    for (i = 0; i < NUMKEYS(psrc); i++, j++) {
      rc = mdbx_node_add(cdst, j, &key, NULL, 0, 0);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
      key.iov_base = (char *)key.iov_base + key.iov_len;
    }
  } else {
    for (i = 0; i < NUMKEYS(psrc); i++, j++) {
      srcnode = NODEPTR(psrc, i);
      if (i == 0 && IS_BRANCH(psrc)) {
        MDBX_cursor mn;
        MDBX_node *s2;
        mdbx_cursor_copy(csrc, &mn);
        mn.mc_xcursor = NULL;
        /* must find the lowest key below src */
        rc = mdbx_page_search_lowest(&mn);
        if (unlikely(rc))
          return rc;
        if (IS_LEAF2(mn.mc_pg[mn.mc_top])) {
          key.iov_len = mn.mc_db->md_xsize;
          key.iov_base = LEAF2KEY(mn.mc_pg[mn.mc_top], 0, key.iov_len);
        } else {
          s2 = NODEPTR(mn.mc_pg[mn.mc_top], 0);
          key.iov_len = NODEKSZ(s2);
          key.iov_base = NODEKEY(s2);
        }
      } else {
        key.iov_len = srcnode->mn_ksize;
        key.iov_base = NODEKEY(srcnode);
      }

      data.iov_len = NODEDSZ(srcnode);
      data.iov_base = NODEDATA(srcnode);
      rc = mdbx_node_add(cdst, j, &key, &data, NODEPGNO(srcnode),
                         srcnode->mn_flags);
      if (unlikely(rc != MDBX_SUCCESS))
        return rc;
    }
  }

  mdbx_debug("dst page %" PRIaPGNO " now has %u keys (%.1f%% filled)",
             pdst->mp_pgno, NUMKEYS(pdst),
             (float)PAGEFILL(cdst->mc_txn->mt_env, pdst) / 10);

  /* Unlink the src page from parent and add to free list. */
  csrc->mc_top--;
  mdbx_node_del(csrc, 0);
  if (csrc->mc_ki[csrc->mc_top] == 0) {
    key.iov_len = 0;
    rc = mdbx_update_key(csrc, &key);
    if (unlikely(rc)) {
      csrc->mc_top++;
      return rc;
    }
  }
  csrc->mc_top++;

  psrc = csrc->mc_pg[csrc->mc_top];
  /* If not operating on FreeDB, allow this page to be reused
   * in this txn. Otherwise just add to free list. */
  rc = mdbx_page_loose(csrc, psrc);
  if (unlikely(rc))
    return rc;
  if (IS_LEAF(psrc))
    csrc->mc_db->md_leaf_pages--;
  else
    csrc->mc_db->md_branch_pages--;
  {
    /* Adjust other cursors pointing to mp */
    MDBX_cursor *m2, *m3;
    MDBX_dbi dbi = csrc->mc_dbi;
    unsigned top = csrc->mc_top;

    for (m2 = csrc->mc_txn->mt_cursors[dbi]; m2; m2 = m2->mc_next) {
      if (csrc->mc_flags & C_SUB)
        m3 = &m2->mc_xcursor->mx_cursor;
      else
        m3 = m2;
      if (m3 == csrc)
        continue;
      if (m3->mc_snum < csrc->mc_snum)
        continue;
      if (m3->mc_pg[top] == psrc) {
        m3->mc_pg[top] = pdst;
        mdbx_cassert(m3, nkeys + m3->mc_ki[top] <= UINT16_MAX);
        m3->mc_ki[top] += (indx_t)nkeys;
        m3->mc_ki[top - 1] = cdst->mc_ki[top - 1];
      } else if (m3->mc_pg[top - 1] == csrc->mc_pg[top - 1] &&
                 m3->mc_ki[top - 1] > csrc->mc_ki[top - 1]) {
        m3->mc_ki[top - 1]--;
      }
      if (XCURSOR_INITED(m3) && IS_LEAF(psrc))
        XCURSOR_REFRESH(m3, m3->mc_pg[top], m3->mc_ki[top]);
    }
  }
  {
    unsigned snum = cdst->mc_snum;
    uint16_t depth = cdst->mc_db->md_depth;
    mdbx_cursor_pop(cdst);
    rc = mdbx_rebalance(cdst);
    /* Did the tree height change? */
    if (depth != cdst->mc_db->md_depth)
      snum += cdst->mc_db->md_depth - depth;
    mdbx_cassert(cdst, snum >= 1 && snum <= UINT16_MAX);
    cdst->mc_snum = (uint16_t)snum;
    cdst->mc_top = (uint16_t)(snum - 1);
  }
  return rc;
}

/* Copy the contents of a cursor.
 * [in] csrc The cursor to copy from.
 * [out] cdst The cursor to copy to. */
static void mdbx_cursor_copy(const MDBX_cursor *csrc, MDBX_cursor *cdst) {
  unsigned i;

  mdbx_cassert(csrc,
               csrc->mc_txn->mt_txnid >= csrc->mc_txn->mt_env->me_oldest[0]);
  cdst->mc_txn = csrc->mc_txn;
  cdst->mc_dbi = csrc->mc_dbi;
  cdst->mc_db = csrc->mc_db;
  cdst->mc_dbx = csrc->mc_dbx;
  cdst->mc_snum = csrc->mc_snum;
  cdst->mc_top = csrc->mc_top;
  cdst->mc_flags = csrc->mc_flags;

  for (i = 0; i < csrc->mc_snum; i++) {
    cdst->mc_pg[i] = csrc->mc_pg[i];
    cdst->mc_ki[i] = csrc->mc_ki[i];
  }
}

/* Rebalance the tree after a delete operation.
 * [in] mc Cursor pointing to the page where rebalancing should begin.
 * Returns 0 on success, non-zero on failure. */
static int mdbx_rebalance(MDBX_cursor *mc) {
  MDBX_node *node;
  int rc, fromleft;
  unsigned ptop, minkeys, thresh;
  MDBX_cursor mn;
  indx_t oldki;

  if (IS_BRANCH(mc->mc_pg[mc->mc_top])) {
    minkeys = 2;
    thresh = 1;
  } else {
    minkeys = 1;
    thresh = FILL_THRESHOLD;
  }
  mdbx_debug("rebalancing %s page %" PRIaPGNO " (has %u keys, %.1f%% full)",
             IS_LEAF(mc->mc_pg[mc->mc_top]) ? "leaf" : "branch",
             mc->mc_pg[mc->mc_top]->mp_pgno, NUMKEYS(mc->mc_pg[mc->mc_top]),
             (float)PAGEFILL(mc->mc_txn->mt_env, mc->mc_pg[mc->mc_top]) / 10);

  if (PAGEFILL(mc->mc_txn->mt_env, mc->mc_pg[mc->mc_top]) >= thresh &&
      NUMKEYS(mc->mc_pg[mc->mc_top]) >= minkeys) {
    mdbx_debug("no need to rebalance page %" PRIaPGNO ", above fill threshold",
               mc->mc_pg[mc->mc_top]->mp_pgno);
    return MDBX_SUCCESS;
  }

  if (mc->mc_snum < 2) {
    MDBX_page *mp = mc->mc_pg[0];
    unsigned nkeys = NUMKEYS(mp);
    if (IS_SUBP(mp)) {
      mdbx_debug("Can't rebalance a subpage, ignoring");
      return MDBX_SUCCESS;
    }
    if (nkeys == 0) {
      mdbx_debug("tree is completely empty");
      mc->mc_db->md_root = P_INVALID;
      mc->mc_db->md_depth = 0;
      mc->mc_db->md_leaf_pages = 0;
      rc = mdbx_pnl_append(&mc->mc_txn->mt_befree_pages, mp->mp_pgno);
      if (unlikely(rc))
        return rc;
      /* Adjust cursors pointing to mp */
      mc->mc_snum = 0;
      mc->mc_top = 0;
      mc->mc_flags &= ~C_INITIALIZED;
      {
        MDBX_cursor *m2, *m3;
        MDBX_dbi dbi = mc->mc_dbi;

        for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2 = m2->mc_next) {
          if (mc->mc_flags & C_SUB)
            m3 = &m2->mc_xcursor->mx_cursor;
          else
            m3 = m2;
          if (!(m3->mc_flags & C_INITIALIZED) || (m3->mc_snum < mc->mc_snum))
            continue;
          if (m3->mc_pg[0] == mp) {
            m3->mc_snum = 0;
            m3->mc_top = 0;
            m3->mc_flags &= ~C_INITIALIZED;
          }
        }
      }
    } else if (IS_BRANCH(mp) && NUMKEYS(mp) == 1) {
      int i;
      mdbx_debug("collapsing root page!");
      rc = mdbx_pnl_append(&mc->mc_txn->mt_befree_pages, mp->mp_pgno);
      if (unlikely(rc))
        return rc;
      mc->mc_db->md_root = NODEPGNO(NODEPTR(mp, 0));
      rc = mdbx_page_get(mc, mc->mc_db->md_root, &mc->mc_pg[0], NULL);
      if (unlikely(rc))
        return rc;
      mc->mc_db->md_depth--;
      mc->mc_db->md_branch_pages--;
      mc->mc_ki[0] = mc->mc_ki[1];
      for (i = 1; i < mc->mc_db->md_depth; i++) {
        mc->mc_pg[i] = mc->mc_pg[i + 1];
        mc->mc_ki[i] = mc->mc_ki[i + 1];
      }
      {
        /* Adjust other cursors pointing to mp */
        MDBX_cursor *m2, *m3;
        MDBX_dbi dbi = mc->mc_dbi;

        for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2 = m2->mc_next) {
          if (mc->mc_flags & C_SUB)
            m3 = &m2->mc_xcursor->mx_cursor;
          else
            m3 = m2;
          if (m3 == mc)
            continue;
          if (!(m3->mc_flags & C_INITIALIZED))
            continue;
          if (m3->mc_pg[0] == mp) {
            for (i = 0; i < mc->mc_db->md_depth; i++) {
              m3->mc_pg[i] = m3->mc_pg[i + 1];
              m3->mc_ki[i] = m3->mc_ki[i + 1];
            }
            m3->mc_snum--;
            m3->mc_top--;
          }
        }
      }
    } else {
      mdbx_debug("root page %" PRIaPGNO
                 " doesn't need rebalancing (flags 0x%x)",
                 mp->mp_pgno, mp->mp_flags);
    }
    return MDBX_SUCCESS;
  }

  /* The parent (branch page) must have at least 2 pointers,
   * otherwise the tree is invalid. */
  ptop = mc->mc_top - 1;
  mdbx_cassert(mc, NUMKEYS(mc->mc_pg[ptop]) > 1);

  /* Leaf page fill factor is below the threshold.
   * Try to move keys from left or right neighbor, or
   * merge with a neighbor page. */

  /* Find neighbors. */
  mdbx_cursor_copy(mc, &mn);
  mn.mc_xcursor = NULL;

  oldki = mc->mc_ki[mc->mc_top];
  if (mc->mc_ki[ptop] == 0) {
    /* We're the leftmost leaf in our parent. */
    mdbx_debug("reading right neighbor");
    mn.mc_ki[ptop]++;
    node = NODEPTR(mc->mc_pg[ptop], mn.mc_ki[ptop]);
    rc = mdbx_page_get(mc, NODEPGNO(node), &mn.mc_pg[mn.mc_top], NULL);
    if (unlikely(rc))
      return rc;
    mn.mc_ki[mn.mc_top] = 0;
    mc->mc_ki[mc->mc_top] = NUMKEYS(mc->mc_pg[mc->mc_top]);
    fromleft = 0;
  } else {
    /* There is at least one neighbor to the left. */
    mdbx_debug("reading left neighbor");
    mn.mc_ki[ptop]--;
    node = NODEPTR(mc->mc_pg[ptop], mn.mc_ki[ptop]);
    rc = mdbx_page_get(mc, NODEPGNO(node), &mn.mc_pg[mn.mc_top], NULL);
    if (unlikely(rc))
      return rc;
    mn.mc_ki[mn.mc_top] = NUMKEYS(mn.mc_pg[mn.mc_top]) - 1;
    mc->mc_ki[mc->mc_top] = 0;
    fromleft = 1;
  }

  mdbx_debug("found neighbor page %" PRIaPGNO " (%u keys, %.1f%% full)",
             mn.mc_pg[mn.mc_top]->mp_pgno, NUMKEYS(mn.mc_pg[mn.mc_top]),
             (float)PAGEFILL(mc->mc_txn->mt_env, mn.mc_pg[mn.mc_top]) / 10);

  /* If the neighbor page is above threshold and has enough keys,
   * move one key from it. Otherwise we should try to merge them.
   * (A branch page must never have less than 2 keys.) */
  if (PAGEFILL(mc->mc_txn->mt_env, mn.mc_pg[mn.mc_top]) >= thresh &&
      NUMKEYS(mn.mc_pg[mn.mc_top]) > minkeys) {
    rc = mdbx_node_move(&mn, mc, fromleft);
    if (fromleft) {
      /* if we inserted on left, bump position up */
      oldki++;
    }
  } else {
    if (!fromleft) {
      rc = mdbx_page_merge(&mn, mc);
    } else {
      oldki += NUMKEYS(mn.mc_pg[mn.mc_top]);
      mn.mc_ki[mn.mc_top] += mc->mc_ki[mn.mc_top] + 1;
      /* We want mdbx_rebalance to find mn when doing fixups */
      WITH_CURSOR_TRACKING(mn, rc = mdbx_page_merge(mc, &mn));
      mdbx_cursor_copy(&mn, mc);
    }
    mc->mc_flags &= ~C_EOF;
  }
  mc->mc_ki[mc->mc_top] = oldki;
  return rc;
}

/* Complete a delete operation started by mdbx_cursor_del(). */
static int mdbx_cursor_del0(MDBX_cursor *mc) {
  int rc;
  MDBX_page *mp;
  indx_t ki;
  unsigned nkeys;
  MDBX_cursor *m2, *m3;
  MDBX_dbi dbi = mc->mc_dbi;

  ki = mc->mc_ki[mc->mc_top];
  mp = mc->mc_pg[mc->mc_top];
  mdbx_node_del(mc, mc->mc_db->md_xsize);
  mc->mc_db->md_entries--;
  {
    /* Adjust other cursors pointing to mp */
    for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2 = m2->mc_next) {
      m3 = (mc->mc_flags & C_SUB) ? &m2->mc_xcursor->mx_cursor : m2;
      if (!(m2->mc_flags & m3->mc_flags & C_INITIALIZED))
        continue;
      if (m3 == mc || m3->mc_snum < mc->mc_snum)
        continue;
      if (m3->mc_pg[mc->mc_top] == mp) {
        if (m3->mc_ki[mc->mc_top] == ki) {
          m3->mc_flags |= C_DEL;
          if (mc->mc_db->md_flags & MDBX_DUPSORT) {
            /* Sub-cursor referred into dataset which is gone */
            m3->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED | C_EOF);
          }
          continue;
        } else if (m3->mc_ki[mc->mc_top] > ki) {
          m3->mc_ki[mc->mc_top]--;
        }
        if (XCURSOR_INITED(m3))
          XCURSOR_REFRESH(m3, m3->mc_pg[mc->mc_top], m3->mc_ki[mc->mc_top]);
      }
    }
  }
  rc = mdbx_rebalance(mc);

  if (likely(rc == MDBX_SUCCESS)) {
    /* DB is totally empty now, just bail out.
     * Other cursors adjustments were already done
     * by mdbx_rebalance and aren't needed here. */
    if (!mc->mc_snum) {
      mc->mc_flags |= C_DEL | C_EOF;
      return rc;
    }

    mp = mc->mc_pg[mc->mc_top];
    nkeys = NUMKEYS(mp);

    /* Adjust other cursors pointing to mp */
    for (m2 = mc->mc_txn->mt_cursors[dbi]; !rc && m2; m2 = m2->mc_next) {
      m3 = (mc->mc_flags & C_SUB) ? &m2->mc_xcursor->mx_cursor : m2;
      if (!(m2->mc_flags & m3->mc_flags & C_INITIALIZED))
        continue;
      if (m3->mc_snum < mc->mc_snum)
        continue;
      if (m3->mc_pg[mc->mc_top] == mp) {
        /* if m3 points past last node in page, find next sibling */
        if (m3->mc_ki[mc->mc_top] >= mc->mc_ki[mc->mc_top]) {
          if (m3->mc_ki[mc->mc_top] >= nkeys) {
            rc = mdbx_cursor_sibling(m3, 1);
            if (rc == MDBX_NOTFOUND) {
              m3->mc_flags |= C_EOF;
              rc = MDBX_SUCCESS;
              continue;
            }
          }
          if (mc->mc_db->md_flags & MDBX_DUPSORT) {
            MDBX_node *node =
                NODEPTR(m3->mc_pg[m3->mc_top], m3->mc_ki[m3->mc_top]);
            /* If this node has dupdata, it may need to be reinited
             * because its data has moved.
             * If the xcursor was not initd it must be reinited.
             * Else if node points to a subDB, nothing is needed. */
            if (node->mn_flags & F_DUPDATA) {
              if (m3->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) {
                if (!(node->mn_flags & F_SUBDATA))
                  m3->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(node);
              } else {
                mdbx_xcursor_init1(m3, node);
                m3->mc_xcursor->mx_cursor.mc_flags |= C_DEL;
              }
            }
          }
        }
      }
    }
    mc->mc_flags |= C_DEL;
  }

  if (unlikely(rc))
    mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
  return rc;
}

int mdbx_del(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data) {
  if (unlikely(!key || !txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_USRVALID)))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_flags & (MDBX_TXN_RDONLY | MDBX_TXN_BLOCKED)))
    return (txn->mt_flags & MDBX_TXN_RDONLY) ? MDBX_EACCESS : MDBX_BAD_TXN;

  return mdbx_del0(txn, dbi, key, data, 0);
}

static int mdbx_del0(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
                     unsigned flags) {
  MDBX_cursor mc;
  MDBX_xcursor mx;
  MDBX_cursor_op op;
  MDBX_val rdata;
  int rc, exact = 0;
  DKBUF;

  mdbx_debug("====> delete db %u key [%s], data [%s]", dbi, DKEY(key),
             DVAL(data));

  mdbx_cursor_init(&mc, txn, dbi, &mx);

  if (data) {
    op = MDBX_GET_BOTH;
    rdata = *data;
    data = &rdata;
  } else {
    op = MDBX_SET;
    flags |= MDBX_NODUPDATA;
  }
  rc = mdbx_cursor_set(&mc, key, data, op, &exact);
  if (likely(rc == MDBX_SUCCESS)) {
    /* let mdbx_page_split know about this cursor if needed:
     * delete will trigger a rebalance; if it needs to move
     * a node from one page to another, it will have to
     * update the parent's separator key(s). If the new sepkey
     * is larger than the current one, the parent page may
     * run out of space, triggering a split. We need this
     * cursor to be consistent until the end of the rebalance. */
    mc.mc_next = txn->mt_cursors[dbi];
    txn->mt_cursors[dbi] = &mc;
    rc = mdbx_cursor_del(&mc, flags);
    txn->mt_cursors[dbi] = mc.mc_next;
  }
  return rc;
}

/* Split a page and insert a new node.
 * Set MDBX_TXN_ERROR on failure.
 * [in,out] mc Cursor pointing to the page and desired insertion index.
 * The cursor will be updated to point to the actual page and index where
 * the node got inserted after the split.
 * [in] newkey The key for the newly inserted node.
 * [in] newdata The data for the newly inserted node.
 * [in] newpgno The page number, if the new node is a branch node.
 * [in] nflags The NODE_ADD_FLAGS for the new node.
 * Returns 0 on success, non-zero on failure. */
static int mdbx_page_split(MDBX_cursor *mc, MDBX_val *newkey, MDBX_val *newdata,
                           pgno_t newpgno, unsigned nflags) {
  unsigned flags;
  int rc = MDBX_SUCCESS, new_root = 0, did_split = 0;
  pgno_t pgno = 0;
  unsigned i, ptop;
  MDBX_env *env = mc->mc_txn->mt_env;
  MDBX_node *node;
  MDBX_val sepkey, rkey, xdata, *rdata = &xdata;
  MDBX_page *copy = NULL;
  MDBX_page *rp, *pp;
  MDBX_cursor mn;
  DKBUF;

  MDBX_page *mp = mc->mc_pg[mc->mc_top];
  unsigned newindx = mc->mc_ki[mc->mc_top];
  unsigned nkeys = NUMKEYS(mp);

  mdbx_debug("-----> splitting %s page %" PRIaPGNO
             " and adding [%s] at index %i/%i",
             IS_LEAF(mp) ? "leaf" : "branch", mp->mp_pgno, DKEY(newkey),
             mc->mc_ki[mc->mc_top], nkeys);

  /* Create a right sibling. */
  if ((rc = mdbx_page_new(mc, mp->mp_flags, 1, &rp)))
    return rc;
  rp->mp_leaf2_ksize = mp->mp_leaf2_ksize;
  mdbx_debug("new right sibling: page %" PRIaPGNO "", rp->mp_pgno);

  /* Usually when splitting the root page, the cursor
   * height is 1. But when called from mdbx_update_key,
   * the cursor height may be greater because it walks
   * up the stack while finding the branch slot to update. */
  if (mc->mc_top < 1) {
    if ((rc = mdbx_page_new(mc, P_BRANCH, 1, &pp)))
      goto done;
    /* shift current top to make room for new parent */
    for (i = mc->mc_snum; i > 0; i--) {
      mc->mc_pg[i] = mc->mc_pg[i - 1];
      mc->mc_ki[i] = mc->mc_ki[i - 1];
    }
    mc->mc_pg[0] = pp;
    mc->mc_ki[0] = 0;
    mc->mc_db->md_root = pp->mp_pgno;
    mdbx_debug("root split! new root = %" PRIaPGNO "", pp->mp_pgno);
    new_root = mc->mc_db->md_depth++;

    /* Add left (implicit) pointer. */
    if (unlikely((rc = mdbx_node_add(mc, 0, NULL, NULL, mp->mp_pgno, 0)) !=
                 MDBX_SUCCESS)) {
      /* undo the pre-push */
      mc->mc_pg[0] = mc->mc_pg[1];
      mc->mc_ki[0] = mc->mc_ki[1];
      mc->mc_db->md_root = mp->mp_pgno;
      mc->mc_db->md_depth--;
      goto done;
    }
    mc->mc_snum++;
    mc->mc_top++;
    ptop = 0;
  } else {
    ptop = mc->mc_top - 1;
    mdbx_debug("parent branch page is %" PRIaPGNO "", mc->mc_pg[ptop]->mp_pgno);
  }

  mdbx_cursor_copy(mc, &mn);
  mn.mc_xcursor = NULL;
  mn.mc_pg[mn.mc_top] = rp;
  mn.mc_ki[ptop] = mc->mc_ki[ptop] + 1;

  unsigned split_indx;
  if (nflags & MDBX_APPEND) {
    mn.mc_ki[mn.mc_top] = 0;
    sepkey = *newkey;
    split_indx = newindx;
    nkeys = 0;
  } else {
    split_indx = (nkeys + 1) / 2;

    if (IS_LEAF2(rp)) {
      char *split, *ins;
      int x;
      unsigned lsize, rsize, ksize;
      /* Move half of the keys to the right sibling */
      x = mc->mc_ki[mc->mc_top] - split_indx;
      ksize = mc->mc_db->md_xsize;
      split = LEAF2KEY(mp, split_indx, ksize);
      rsize = (nkeys - split_indx) * ksize;
      lsize = (nkeys - split_indx) * sizeof(indx_t);
      mdbx_cassert(mc, mp->mp_lower >= lsize);
      mp->mp_lower -= (indx_t)lsize;
      mdbx_cassert(mc, rp->mp_lower + lsize <= UINT16_MAX);
      rp->mp_lower += (indx_t)lsize;
      mdbx_cassert(mc, mp->mp_upper + rsize - lsize <= UINT16_MAX);
      mp->mp_upper += (indx_t)(rsize - lsize);
      mdbx_cassert(mc, rp->mp_upper >= rsize - lsize);
      rp->mp_upper -= (indx_t)(rsize - lsize);
      sepkey.iov_len = ksize;
      if (newindx == split_indx) {
        sepkey.iov_base = newkey->iov_base;
      } else {
        sepkey.iov_base = split;
      }
      if (x < 0) {
        mdbx_cassert(mc, ksize >= sizeof(indx_t));
        ins = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], ksize);
        memcpy(rp->mp_ptrs, split, rsize);
        sepkey.iov_base = rp->mp_ptrs;
        memmove(ins + ksize, ins, (split_indx - mc->mc_ki[mc->mc_top]) * ksize);
        memcpy(ins, newkey->iov_base, ksize);
        mdbx_cassert(mc, UINT16_MAX - mp->mp_lower >= (int)sizeof(indx_t));
        mp->mp_lower += sizeof(indx_t);
        mdbx_cassert(mc, mp->mp_upper >= ksize - sizeof(indx_t));
        mp->mp_upper -= (indx_t)(ksize - sizeof(indx_t));
      } else {
        if (x)
          memcpy(rp->mp_ptrs, split, x * ksize);
        ins = LEAF2KEY(rp, x, ksize);
        memcpy(ins, newkey->iov_base, ksize);
        memcpy(ins + ksize, split + x * ksize, rsize - x * ksize);
        mdbx_cassert(mc, UINT16_MAX - rp->mp_lower >= (int)sizeof(indx_t));
        rp->mp_lower += sizeof(indx_t);
        mdbx_cassert(mc, rp->mp_upper >= ksize - sizeof(indx_t));
        rp->mp_upper -= (indx_t)(ksize - sizeof(indx_t));
        mdbx_cassert(mc, x <= UINT16_MAX);
        mc->mc_ki[mc->mc_top] = (indx_t)x;
      }
    } else {
      size_t psize, nsize, k;
      /* Maximum free space in an empty page */
      unsigned pmax = env->me_psize - PAGEHDRSZ;
      if (IS_LEAF(mp))
        nsize = mdbx_leaf_size(env, newkey, newdata);
      else
        nsize = mdbx_branch_size(env, newkey);
      nsize = EVEN(nsize);

      /* grab a page to hold a temporary copy */
      copy = mdbx_page_malloc(mc->mc_txn, 1);
      if (unlikely(copy == NULL)) {
        rc = MDBX_ENOMEM;
        goto done;
      }
      copy->mp_pgno = mp->mp_pgno;
      copy->mp_flags = mp->mp_flags;
      copy->mp_lower = 0;
      mdbx_cassert(mc, env->me_psize - PAGEHDRSZ <= UINT16_MAX);
      copy->mp_upper = (indx_t)(env->me_psize - PAGEHDRSZ);

      /* prepare to insert */
      for (unsigned j = i = 0; i < nkeys; i++) {
        if (i == newindx)
          copy->mp_ptrs[j++] = 0;
        copy->mp_ptrs[j++] = mp->mp_ptrs[i];
      }

      /* When items are relatively large the split point needs
       * to be checked, because being off-by-one will make the
       * difference between success or failure in mdbx_node_add.
       *
       * It's also relevant if a page happens to be laid out
       * such that one half of its nodes are all "small" and
       * the other half of its nodes are "large." If the new
       * item is also "large" and falls on the half with
       * "large" nodes, it also may not fit.
       *
       * As a final tweak, if the new item goes on the last
       * spot on the page (and thus, onto the new page), bias
       * the split so the new page is emptier than the old page.
       * This yields better packing during sequential inserts.
       */
      int dir;
      if (nkeys < 20 || nsize > pmax / 16 || newindx >= nkeys) {
        /* Find split point */
        psize = 0;
        if (newindx <= split_indx || newindx >= nkeys) {
          i = 0;
          dir = 1;
          k = (newindx >= nkeys) ? nkeys : split_indx + 1 + IS_LEAF(mp);
        } else {
          i = nkeys;
          dir = -1;
          k = split_indx - 1;
        }
        for (; i != k; i += dir) {
          if (i == newindx) {
            psize += nsize;
            node = NULL;
          } else {
            node = (MDBX_node *)((char *)mp + copy->mp_ptrs[i] + PAGEHDRSZ);
            psize += NODESIZE + NODEKSZ(node) + sizeof(indx_t);
            if (IS_LEAF(mp)) {
              if (F_ISSET(node->mn_flags, F_BIGDATA))
                psize += sizeof(pgno_t);
              else
                psize += NODEDSZ(node);
            }
            psize = EVEN(psize);
          }
          if (psize > pmax || i == k - dir) {
            split_indx = i + (dir < 0);
            break;
          }
        }
      }
      if (split_indx == newindx) {
        sepkey.iov_len = newkey->iov_len;
        sepkey.iov_base = newkey->iov_base;
      } else {
        node =
            (MDBX_node *)((char *)mp + copy->mp_ptrs[split_indx] + PAGEHDRSZ);
        sepkey.iov_len = node->mn_ksize;
        sepkey.iov_base = NODEKEY(node);
      }
    }
  }

  mdbx_debug("separator is %d [%s]", split_indx, DKEY(&sepkey));

  /* Copy separator key to the parent. */
  if (SIZELEFT(mn.mc_pg[ptop]) < mdbx_branch_size(env, &sepkey)) {
    int snum = mc->mc_snum;
    mn.mc_snum--;
    mn.mc_top--;
    did_split = 1;
    /* We want other splits to find mn when doing fixups */
    WITH_CURSOR_TRACKING(
        mn, rc = mdbx_page_split(&mn, &sepkey, NULL, rp->mp_pgno, 0));
    if (unlikely(rc != MDBX_SUCCESS))
      goto done;

    /* root split? */
    if (mc->mc_snum > snum)
      ptop++;

    /* Right page might now have changed parent.
     * Check if left page also changed parent. */
    if (mn.mc_pg[ptop] != mc->mc_pg[ptop] &&
        mc->mc_ki[ptop] >= NUMKEYS(mc->mc_pg[ptop])) {
      for (i = 0; i < ptop; i++) {
        mc->mc_pg[i] = mn.mc_pg[i];
        mc->mc_ki[i] = mn.mc_ki[i];
      }
      mc->mc_pg[ptop] = mn.mc_pg[ptop];
      if (mn.mc_ki[ptop]) {
        mc->mc_ki[ptop] = mn.mc_ki[ptop] - 1;
      } else {
        /* find right page's left sibling */
        mc->mc_ki[ptop] = mn.mc_ki[ptop];
        rc = mdbx_cursor_sibling(mc, 0);
      }
    }
  } else {
    mn.mc_top--;
    rc = mdbx_node_add(&mn, mn.mc_ki[ptop], &sepkey, NULL, rp->mp_pgno, 0);
    mn.mc_top++;
  }
  if (unlikely(rc != MDBX_SUCCESS)) {
    if (rc == MDBX_NOTFOUND) /* improper mdbx_cursor_sibling() result */ {
      mdbx_error("unexpected %s", "MDBX_NOTFOUND");
      rc = MDBX_PROBLEM;
    }
    goto done;
  }
  if (nflags & MDBX_APPEND) {
    mc->mc_pg[mc->mc_top] = rp;
    mc->mc_ki[mc->mc_top] = 0;
    rc = mdbx_node_add(mc, 0, newkey, newdata, newpgno, nflags);
    if (rc)
      goto done;
    for (i = 0; i < mc->mc_top; i++)
      mc->mc_ki[i] = mn.mc_ki[i];
  } else if (!IS_LEAF2(mp)) {
    /* Move nodes */
    mc->mc_pg[mc->mc_top] = rp;
    i = split_indx;
    indx_t n = 0;
    do {
      if (i == newindx) {
        rkey.iov_base = newkey->iov_base;
        rkey.iov_len = newkey->iov_len;
        if (IS_LEAF(mp)) {
          rdata = newdata;
        } else
          pgno = newpgno;
        flags = nflags;
        /* Update index for the new key. */
        mc->mc_ki[mc->mc_top] = n;
      } else {
        node = (MDBX_node *)((char *)mp + copy->mp_ptrs[i] + PAGEHDRSZ);
        rkey.iov_base = NODEKEY(node);
        rkey.iov_len = node->mn_ksize;
        if (IS_LEAF(mp)) {
          xdata.iov_base = NODEDATA(node);
          xdata.iov_len = NODEDSZ(node);
          rdata = &xdata;
        } else
          pgno = NODEPGNO(node);
        flags = node->mn_flags;
      }

      if (!IS_LEAF(mp) && n == 0) {
        /* First branch index doesn't need key data. */
        rkey.iov_len = 0;
      }

      rc = mdbx_node_add(mc, n, &rkey, rdata, pgno, flags);
      if (rc)
        goto done;
      if (i == nkeys) {
        i = 0;
        n = 0;
        mc->mc_pg[mc->mc_top] = copy;
      } else {
        i++;
        n++;
      }
    } while (i != split_indx);

    nkeys = NUMKEYS(copy);
    for (i = 0; i < nkeys; i++)
      mp->mp_ptrs[i] = copy->mp_ptrs[i];
    mp->mp_lower = copy->mp_lower;
    mp->mp_upper = copy->mp_upper;
    memcpy(NODEPTR(mp, nkeys - 1), NODEPTR(copy, nkeys - 1),
           env->me_psize - copy->mp_upper - PAGEHDRSZ);

    /* reset back to original page */
    if (newindx < split_indx) {
      mc->mc_pg[mc->mc_top] = mp;
    } else {
      mc->mc_pg[mc->mc_top] = rp;
      mc->mc_ki[ptop]++;
      /* Make sure mc_ki is still valid. */
      if (mn.mc_pg[ptop] != mc->mc_pg[ptop] &&
          mc->mc_ki[ptop] >= NUMKEYS(mc->mc_pg[ptop])) {
        for (i = 0; i <= ptop; i++) {
          mc->mc_pg[i] = mn.mc_pg[i];
          mc->mc_ki[i] = mn.mc_ki[i];
        }
      }
    }
    if (nflags & MDBX_RESERVE) {
      node = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
      if (!(node->mn_flags & F_BIGDATA))
        newdata->iov_base = NODEDATA(node);
    }
  } else {
    if (newindx >= split_indx) {
      mc->mc_pg[mc->mc_top] = rp;
      mc->mc_ki[ptop]++;
      /* Make sure mc_ki is still valid. */
      if (mn.mc_pg[ptop] != mc->mc_pg[ptop] &&
          mc->mc_ki[ptop] >= NUMKEYS(mc->mc_pg[ptop])) {
        for (i = 0; i <= ptop; i++) {
          mc->mc_pg[i] = mn.mc_pg[i];
          mc->mc_ki[i] = mn.mc_ki[i];
        }
      }
    }
  }

  {
    /* Adjust other cursors pointing to mp */
    MDBX_cursor *m2, *m3;
    MDBX_dbi dbi = mc->mc_dbi;
    nkeys = NUMKEYS(mp);

    for (m2 = mc->mc_txn->mt_cursors[dbi]; m2; m2 = m2->mc_next) {
      if (mc->mc_flags & C_SUB)
        m3 = &m2->mc_xcursor->mx_cursor;
      else
        m3 = m2;
      if (m3 == mc)
        continue;
      if (!(m2->mc_flags & m3->mc_flags & C_INITIALIZED))
        continue;
      if (new_root) {
        int k;
        /* sub cursors may be on different DB */
        if (m3->mc_pg[0] != mp)
          continue;
        /* root split */
        for (k = new_root; k >= 0; k--) {
          m3->mc_ki[k + 1] = m3->mc_ki[k];
          m3->mc_pg[k + 1] = m3->mc_pg[k];
        }
        if (m3->mc_ki[0] >= nkeys) {
          m3->mc_ki[0] = 1;
        } else {
          m3->mc_ki[0] = 0;
        }
        m3->mc_pg[0] = mc->mc_pg[0];
        m3->mc_snum++;
        m3->mc_top++;
      }
      if (m3->mc_top >= mc->mc_top && m3->mc_pg[mc->mc_top] == mp) {
        if (m3->mc_ki[mc->mc_top] >= newindx && !(nflags & MDBX_SPLIT_REPLACE))
          m3->mc_ki[mc->mc_top]++;
        if (m3->mc_ki[mc->mc_top] >= nkeys) {
          m3->mc_pg[mc->mc_top] = rp;
          mdbx_cassert(mc, m3->mc_ki[mc->mc_top] >= nkeys);
          m3->mc_ki[mc->mc_top] -= (indx_t)nkeys;
          for (i = 0; i < mc->mc_top; i++) {
            m3->mc_ki[i] = mn.mc_ki[i];
            m3->mc_pg[i] = mn.mc_pg[i];
          }
        }
      } else if (!did_split && m3->mc_top >= ptop &&
                 m3->mc_pg[ptop] == mc->mc_pg[ptop] &&
                 m3->mc_ki[ptop] >= mc->mc_ki[ptop]) {
        m3->mc_ki[ptop]++;
      }
      if (XCURSOR_INITED(m3) && IS_LEAF(mp))
        XCURSOR_REFRESH(m3, m3->mc_pg[mc->mc_top], m3->mc_ki[mc->mc_top]);
    }
  }
  mdbx_debug("mp left: %d, rp left: %d", SIZELEFT(mp), SIZELEFT(rp));

done:
  if (copy) /* tmp page */
    mdbx_page_free(env, copy);
  if (unlikely(rc))
    mc->mc_txn->mt_flags |= MDBX_TXN_ERROR;
  return rc;
}

int mdbx_put(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
             unsigned flags) {
  MDBX_cursor mc;
  MDBX_xcursor mx;

  if (unlikely(!key || !data || !txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_USRVALID)))
    return MDBX_EINVAL;

  if (unlikely(flags &
               ~(MDBX_NOOVERWRITE | MDBX_NODUPDATA | MDBX_RESERVE |
                 MDBX_APPEND | MDBX_APPENDDUP | MDBX_CURRENT)))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_flags & (MDBX_TXN_RDONLY | MDBX_TXN_BLOCKED)))
    return (txn->mt_flags & MDBX_TXN_RDONLY) ? MDBX_EACCESS : MDBX_BAD_TXN;

  mdbx_cursor_init(&mc, txn, dbi, &mx);
  mc.mc_next = txn->mt_cursors[dbi];
  txn->mt_cursors[dbi] = &mc;

  int rc = MDBX_SUCCESS;
  /* LY: support for update (explicit overwrite) */
  if (flags & MDBX_CURRENT) {
    rc = mdbx_cursor_get(&mc, key, NULL, MDBX_SET);
    if (likely(rc == MDBX_SUCCESS) &&
        (txn->mt_dbs[dbi].md_flags & MDBX_DUPSORT)) {
      /* LY: allows update (explicit overwrite) only for unique keys */
      MDBX_node *leaf = NODEPTR(mc.mc_pg[mc.mc_top], mc.mc_ki[mc.mc_top]);
      if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
        mdbx_tassert(txn, XCURSOR_INITED(&mc) &&
                              mc.mc_xcursor->mx_db.md_entries > 1);
        rc = MDBX_EMULTIVAL;
      }
    }
  }

  if (likely(rc == MDBX_SUCCESS))
    rc = mdbx_cursor_put(&mc, key, data, flags);
  txn->mt_cursors[dbi] = mc.mc_next;

  return rc;
}

#ifndef MDBX_WBUF
#define MDBX_WBUF (1024 * 1024)
#endif
#define MDBX_EOF 0x10 /* mdbx_env_copyfd1() is done reading */

/* State needed for a double-buffering compacting copy. */
typedef struct mdbx_copy {
  MDBX_env *mc_env;
  MDBX_txn *mc_txn;
  mdbx_condmutex_t mc_condmutex;
  char *mc_wbuf[2];
  char *mc_over[2];
  size_t mc_wlen[2];
  size_t mc_olen[2];
  mdbx_filehandle_t mc_fd;
  volatile int mc_error;
  pgno_t mc_next_pgno;
  short mc_toggle; /* Buffer number in provider */
  short mc_new;    /* (0-2 buffers to write) | (MDBX_EOF at end) */
  /* Error code.  Never cleared if set.  Both threads can set nonzero
   * to fail the copy.  Not mutex-protected, MDBX expects atomic int. */
} mdbx_copy;

/* Dedicated writer thread for compacting copy. */
static THREAD_RESULT __cold THREAD_CALL mdbx_env_copythr(void *arg) {
  mdbx_copy *my = arg;
  char *ptr;
  int toggle = 0;
  int rc;

#if defined(F_SETNOSIGPIPE)
  /* OS X delivers SIGPIPE to the whole process, not the thread that caused it.
   * Disable SIGPIPE using platform specific fcntl. */
  int enabled = 1;
  if (fcntl(my->mc_fd, F_SETNOSIGPIPE, &enabled))
    my->mc_error = errno;
#endif

#if defined(SIGPIPE) && !defined(_WIN32) && !defined(_WIN64)
  sigset_t set;
  sigemptyset(&set);
  sigaddset(&set, SIGPIPE);
  rc = pthread_sigmask(SIG_BLOCK, &set, NULL);
  if (rc != 0)
    my->mc_error = rc;
#endif

  mdbx_condmutex_lock(&my->mc_condmutex);
  while (!my->mc_error) {
    while (!my->mc_new)
      mdbx_condmutex_wait(&my->mc_condmutex);
    if (my->mc_new == 0 + MDBX_EOF) /* 0 buffers, just EOF */
      break;
    size_t wsize = my->mc_wlen[toggle];
    ptr = my->mc_wbuf[toggle];
  again:
    if (wsize > 0 && !my->mc_error) {
      rc = mdbx_write(my->mc_fd, ptr, wsize);
      if (rc != MDBX_SUCCESS) {
#if defined(SIGPIPE) && !defined(_WIN32) && !defined(_WIN64)
        if (rc == EPIPE) {
          /* Collect the pending SIGPIPE, otherwise (at least OS X)
           * gives it to the process on thread-exit (ITS#8504). */
          int tmp;
          sigwait(&set, &tmp);
        }
#endif
        my->mc_error = rc;
      }
    }

    /* If there's an overflow page tail, write it too */
    if (my->mc_olen[toggle]) {
      wsize = my->mc_olen[toggle];
      ptr = my->mc_over[toggle];
      my->mc_olen[toggle] = 0;
      goto again;
    }
    my->mc_wlen[toggle] = 0;
    toggle ^= 1;
    /* Return the empty buffer to provider */
    my->mc_new--;
    mdbx_condmutex_signal(&my->mc_condmutex);
  }
  mdbx_condmutex_unlock(&my->mc_condmutex);
  return (THREAD_RESULT)0;
}

/* Give buffer and/or MDBX_EOF to writer thread, await unused buffer.
 *
 * [in] my control structure.
 * [in] adjust (1 to hand off 1 buffer) | (MDBX_EOF when ending). */
static int __cold mdbx_env_cthr_toggle(mdbx_copy *my, int adjust) {
  mdbx_condmutex_lock(&my->mc_condmutex);
  my->mc_new += (short)adjust;
  mdbx_condmutex_signal(&my->mc_condmutex);
  while (my->mc_new & 2) /* both buffers in use */
    mdbx_condmutex_wait(&my->mc_condmutex);
  mdbx_condmutex_unlock(&my->mc_condmutex);

  my->mc_toggle ^= (adjust & 1);
  /* Both threads reset mc_wlen, to be safe from threading errors */
  my->mc_wlen[my->mc_toggle] = 0;
  return my->mc_error;
}

/* Depth-first tree traversal for compacting copy.
 * [in] my control structure.
 * [in,out] pg database root.
 * [in] flags includes F_DUPDATA if it is a sorted-duplicate sub-DB. */
static int __cold mdbx_env_cwalk(mdbx_copy *my, pgno_t *pg, int flags) {
  MDBX_cursor mc;
  MDBX_node *ni;
  MDBX_page *mo, *mp, *leaf;
  char *buf, *ptr;
  int rc, toggle;
  unsigned i;

  /* Empty DB, nothing to do */
  if (*pg == P_INVALID)
    return MDBX_SUCCESS;

  memset(&mc, 0, sizeof(mc));
  mc.mc_snum = 1;
  mc.mc_txn = my->mc_txn;

  rc = mdbx_page_get(&mc, *pg, &mc.mc_pg[0], NULL);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;
  rc = mdbx_page_search_root(&mc, NULL, MDBX_PS_FIRST);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;

  /* Make cursor pages writable */
  buf = ptr = malloc(pgno2bytes(my->mc_env, mc.mc_snum));
  if (buf == NULL)
    return MDBX_ENOMEM;

  for (i = 0; i < mc.mc_top; i++) {
    mdbx_page_copy((MDBX_page *)ptr, mc.mc_pg[i], my->mc_env->me_psize);
    mc.mc_pg[i] = (MDBX_page *)ptr;
    ptr += my->mc_env->me_psize;
  }

  /* This is writable space for a leaf page. Usually not needed. */
  leaf = (MDBX_page *)ptr;

  toggle = my->mc_toggle;
  while (mc.mc_snum > 0) {
    unsigned n;
    mp = mc.mc_pg[mc.mc_top];
    n = NUMKEYS(mp);

    if (IS_LEAF(mp)) {
      if (!IS_LEAF2(mp) && !(flags & F_DUPDATA)) {
        for (i = 0; i < n; i++) {
          ni = NODEPTR(mp, i);
          if (ni->mn_flags & F_BIGDATA) {
            MDBX_page *omp;

            /* Need writable leaf */
            if (mp != leaf) {
              mc.mc_pg[mc.mc_top] = leaf;
              mdbx_page_copy(leaf, mp, my->mc_env->me_psize);
              mp = leaf;
              ni = NODEPTR(mp, i);
            }

            pgno_t pgno;
            memcpy(&pgno, NODEDATA(ni), sizeof(pgno));
            memcpy(NODEDATA(ni), &my->mc_next_pgno, sizeof(pgno_t));
            rc = mdbx_page_get(&mc, pgno, &omp, NULL);
            if (unlikely(rc != MDBX_SUCCESS))
              goto done;
            if (my->mc_wlen[toggle] >= MDBX_WBUF) {
              rc = mdbx_env_cthr_toggle(my, 1);
              if (unlikely(rc != MDBX_SUCCESS))
                goto done;
              toggle = my->mc_toggle;
            }
            mo = (MDBX_page *)(my->mc_wbuf[toggle] + my->mc_wlen[toggle]);
            memcpy(mo, omp, my->mc_env->me_psize);
            mo->mp_pgno = my->mc_next_pgno;
            my->mc_next_pgno += omp->mp_pages;
            my->mc_wlen[toggle] += my->mc_env->me_psize;
            if (omp->mp_pages > 1) {
              my->mc_olen[toggle] = pgno2bytes(my->mc_env, omp->mp_pages - 1);
              my->mc_over[toggle] = (char *)omp + my->mc_env->me_psize;
              rc = mdbx_env_cthr_toggle(my, 1);
              if (unlikely(rc != MDBX_SUCCESS))
                goto done;
              toggle = my->mc_toggle;
            }
          } else if (ni->mn_flags & F_SUBDATA) {
            MDBX_db db;

            /* Need writable leaf */
            if (mp != leaf) {
              mc.mc_pg[mc.mc_top] = leaf;
              mdbx_page_copy(leaf, mp, my->mc_env->me_psize);
              mp = leaf;
              ni = NODEPTR(mp, i);
            }

            memcpy(&db, NODEDATA(ni), sizeof(db));
            my->mc_toggle = (short)toggle;
            rc = mdbx_env_cwalk(my, &db.md_root, ni->mn_flags & F_DUPDATA);
            if (rc)
              goto done;
            toggle = my->mc_toggle;
            memcpy(NODEDATA(ni), &db, sizeof(db));
          }
        }
      }
    } else {
      mc.mc_ki[mc.mc_top]++;
      if (mc.mc_ki[mc.mc_top] < n) {
        pgno_t pgno;
      again:
        ni = NODEPTR(mp, mc.mc_ki[mc.mc_top]);
        pgno = NODEPGNO(ni);
        rc = mdbx_page_get(&mc, pgno, &mp, NULL);
        if (unlikely(rc != MDBX_SUCCESS))
          goto done;
        mc.mc_top++;
        mc.mc_snum++;
        mc.mc_ki[mc.mc_top] = 0;
        if (IS_BRANCH(mp)) {
          /* Whenever we advance to a sibling branch page,
           * we must proceed all the way down to its first leaf. */
          mdbx_page_copy(mc.mc_pg[mc.mc_top], mp, my->mc_env->me_psize);
          goto again;
        } else
          mc.mc_pg[mc.mc_top] = mp;
        continue;
      }
    }
    if (my->mc_wlen[toggle] >= MDBX_WBUF) {
      rc = mdbx_env_cthr_toggle(my, 1);
      if (unlikely(rc != MDBX_SUCCESS))
        goto done;
      toggle = my->mc_toggle;
    }
    mo = (MDBX_page *)(my->mc_wbuf[toggle] + my->mc_wlen[toggle]);
    mdbx_page_copy(mo, mp, my->mc_env->me_psize);
    mo->mp_pgno = my->mc_next_pgno++;
    my->mc_wlen[toggle] += my->mc_env->me_psize;
    if (mc.mc_top) {
      /* Update parent if there is one */
      ni = NODEPTR(mc.mc_pg[mc.mc_top - 1], mc.mc_ki[mc.mc_top - 1]);
      SETPGNO(ni, mo->mp_pgno);
      mdbx_cursor_pop(&mc);
    } else {
      /* Otherwise we're done */
      *pg = mo->mp_pgno;
      break;
    }
  }
done:
  free(buf);
  return rc;
}

/* Copy environment with compaction. */
static int __cold mdbx_env_compact(MDBX_env *env, mdbx_filehandle_t fd) {
  MDBX_txn *txn = NULL;
  mdbx_thread_t thr;
  mdbx_copy my;
  memset(&my, 0, sizeof(my));

  int rc = mdbx_condmutex_init(&my.mc_condmutex);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;
  rc = mdbx_memalign_alloc(env->me_os_psize, MDBX_WBUF * 2,
                           (void **)&my.mc_wbuf[0]);
  if (unlikely(rc != MDBX_SUCCESS))
    goto done;

  memset(my.mc_wbuf[0], 0, MDBX_WBUF * 2);
  my.mc_wbuf[1] = my.mc_wbuf[0] + MDBX_WBUF;
  my.mc_next_pgno = NUM_METAS;
  my.mc_env = env;
  my.mc_fd = fd;
  rc = mdbx_thread_create(&thr, mdbx_env_copythr, &my);
  if (unlikely(rc != MDBX_SUCCESS))
    goto done;

  rc = mdbx_txn_begin(env, NULL, MDBX_RDONLY, &txn);
  if (unlikely(rc != MDBX_SUCCESS))
    goto finish;

  MDBX_page *meta = mdbx_init_metas(env, my.mc_wbuf[0]);

  /* Set metapage 1 with current main DB */
  pgno_t new_root, root = txn->mt_dbs[MAIN_DBI].md_root;
  if ((new_root = root) != P_INVALID) {
    /* Count free pages + freeDB pages.  Subtract from last_pg
     * to find the new last_pg, which also becomes the new root. */
    pgno_t freecount = 0;
    MDBX_cursor mc;
    MDBX_val key, data;

    mdbx_cursor_init(&mc, txn, FREE_DBI, NULL);
    while ((rc = mdbx_cursor_get(&mc, &key, &data, MDBX_NEXT)) == 0)
      freecount += *(pgno_t *)data.iov_base;
    if (unlikely(rc != MDBX_NOTFOUND))
      goto finish;

    freecount += txn->mt_dbs[FREE_DBI].md_branch_pages +
                 txn->mt_dbs[FREE_DBI].md_leaf_pages +
                 txn->mt_dbs[FREE_DBI].md_overflow_pages;

    new_root = txn->mt_next_pgno - 1 - freecount;
    meta->mp_meta.mm_geo.next = meta->mp_meta.mm_geo.now = new_root + 1;
    meta->mp_meta.mm_dbs[MAIN_DBI] = txn->mt_dbs[MAIN_DBI];
    meta->mp_meta.mm_dbs[MAIN_DBI].md_root = new_root;
  } else {
    /* When the DB is empty, handle it specially to
     * fix any breakage like page leaks from ITS#8174. */
    meta->mp_meta.mm_dbs[MAIN_DBI].md_flags = txn->mt_dbs[MAIN_DBI].md_flags;
  }

  /* copy canary sequenses if present */
  if (txn->mt_canary.v) {
    meta->mp_meta.mm_canary = txn->mt_canary;
    meta->mp_meta.mm_canary.v = mdbx_meta_txnid_stable(env, &meta->mp_meta);
  }

  /* update signature */
  meta->mp_meta.mm_datasync_sign = mdbx_meta_sign(&meta->mp_meta);

  my.mc_wlen[0] = pgno2bytes(env, NUM_METAS);
  my.mc_txn = txn;
  rc = mdbx_env_cwalk(&my, &root, 0);
  if (rc == MDBX_SUCCESS && root != new_root) {
    mdbx_error("unexpected root %" PRIaPGNO " (%" PRIaPGNO ")", root, new_root);
    rc = MDBX_PROBLEM; /* page leak or corrupt DB */
  }

finish:
  if (rc != MDBX_SUCCESS)
    my.mc_error = rc;
  mdbx_env_cthr_toggle(&my, 1 | MDBX_EOF);
  rc = mdbx_thread_join(thr);
  mdbx_txn_abort(txn);

done:
  mdbx_memalign_free(my.mc_wbuf[0]);
  mdbx_condmutex_destroy(&my.mc_condmutex);
  return rc ? rc : my.mc_error;
}

/* Copy environment as-is. */
static int __cold mdbx_env_copy_asis(MDBX_env *env, mdbx_filehandle_t fd) {
  MDBX_txn *txn = NULL;

  /* Do the lock/unlock of the reader mutex before starting the
   * write txn.  Otherwise other read txns could block writers. */
  int rc = mdbx_txn_begin(env, NULL, MDBX_RDONLY, &txn);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;

  /* We must start the actual read txn after blocking writers */
  rc = mdbx_txn_end(txn, MDBX_END_RESET_TMP);
  if (unlikely(rc != MDBX_SUCCESS))
    goto bailout; /* FIXME: or just return? */

  /* Temporarily block writers until we snapshot the meta pages */
  rc = mdbx_txn_lock(env);
  if (unlikely(rc != MDBX_SUCCESS))
    goto bailout;

  rc = mdbx_txn_renew0(txn, MDBX_RDONLY);
  if (unlikely(rc != MDBX_SUCCESS)) {
    mdbx_txn_unlock(env);
    goto bailout;
  }

  rc = mdbx_write(fd, env->me_map, pgno2bytes(env, NUM_METAS));
  MDBX_meta *const head = mdbx_meta_head(env);
  const uint64_t size =
      mdbx_roundup2(pgno2bytes(env, head->mm_geo.now), env->me_os_psize);
  mdbx_txn_unlock(env);

  if (likely(rc == MDBX_SUCCESS))
    rc = mdbx_write(fd, env->me_map + pgno2bytes(env, NUM_METAS),
                    pgno2bytes(env, txn->mt_next_pgno - NUM_METAS));

  if (likely(rc == MDBX_SUCCESS))
    rc = mdbx_ftruncate(fd, size);

bailout:
  mdbx_txn_abort(txn);
  return rc;
}

int __cold mdbx_env_copy2fd(MDBX_env *env, mdbx_filehandle_t fd,
                            unsigned flags) {
  if (flags & MDBX_CP_COMPACT)
    return mdbx_env_compact(env, fd);

  return mdbx_env_copy_asis(env, fd);
}

int __cold mdbx_env_copy(MDBX_env *env, const char *path, unsigned flags) {
  char *lck_pathname;
  mdbx_filehandle_t newfd = INVALID_HANDLE_VALUE;

  if (env->me_flags & MDBX_NOSUBDIR) {
    lck_pathname = (char *)path;
  } else {
    size_t len = strlen(path);
    len += sizeof(MDBX_DATANAME);
    lck_pathname = malloc(len);
    if (!lck_pathname)
      return MDBX_ENOMEM;
    sprintf(lck_pathname, "%s" MDBX_DATANAME, path);
  }

  /* The destination path must exist, but the destination file must not.
   * We don't want the OS to cache the writes, since the source data is
   * already in the OS cache. */
  int rc =
      mdbx_openfile(lck_pathname, O_WRONLY | O_CREAT | O_EXCL, 0666, &newfd);
  if (rc == MDBX_SUCCESS) {
    if (env->me_psize >= env->me_os_psize) {
#ifdef F_NOCACHE /* __APPLE__ */
      (void)fcntl(newfd, F_NOCACHE, 1);
#elif defined(O_DIRECT) && defined(F_GETFL)
      /* Set O_DIRECT if the file system supports it */
      if ((rc = fcntl(newfd, F_GETFL)) != -1)
        (void)fcntl(newfd, F_SETFL, rc | O_DIRECT);
#endif
    }
    rc = mdbx_env_copy2fd(env, newfd, flags);
  }

  if (!(env->me_flags & MDBX_NOSUBDIR))
    free(lck_pathname);

  if (newfd != INVALID_HANDLE_VALUE) {
    int err = mdbx_closefile(newfd);
    if (rc == MDBX_SUCCESS && err != rc)
      rc = err;
  }

  return rc;
}

int __cold mdbx_env_set_flags(MDBX_env *env, unsigned flags, int onoff) {
  if (unlikely(flags & ~CHANGEABLE))
    return MDBX_EINVAL;

  int rc = mdbx_txn_lock(env);
  if (unlikely(rc))
    return rc;

  if (onoff)
    env->me_flags |= flags;
  else
    env->me_flags &= ~flags;

  mdbx_txn_unlock(env);
  return MDBX_SUCCESS;
}

int __cold mdbx_env_get_flags(MDBX_env *env, unsigned *arg) {
  if (unlikely(!env || !arg))
    return MDBX_EINVAL;

  *arg = env->me_flags & (CHANGEABLE | CHANGELESS);
  return MDBX_SUCCESS;
}

int __cold mdbx_env_set_userctx(MDBX_env *env, void *ctx) {
  if (unlikely(!env))
    return MDBX_EINVAL;
  env->me_userctx = ctx;
  return MDBX_SUCCESS;
}

void *__cold mdbx_env_get_userctx(MDBX_env *env) {
  return env ? env->me_userctx : NULL;
}

int __cold mdbx_env_set_assert(MDBX_env *env, MDBX_assert_func *func) {
  if (unlikely(!env))
    return MDBX_EINVAL;
#if MDBX_DEBUG
  env->me_assert_func = func;
  return MDBX_SUCCESS;
#else
  (void)func;
  return MDBX_ENOSYS;
#endif
}

int __cold mdbx_env_get_path(MDBX_env *env, const char **arg) {
  if (unlikely(!env || !arg))
    return MDBX_EINVAL;

  *arg = env->me_path;
  return MDBX_SUCCESS;
}

int __cold mdbx_env_get_fd(MDBX_env *env, mdbx_filehandle_t *arg) {
  if (unlikely(!env || !arg))
    return MDBX_EINVAL;

  *arg = env->me_fd;
  return MDBX_SUCCESS;
}

/* Common code for mdbx_dbi_stat() and mdbx_env_stat().
 * [in] env the environment to operate in.
 * [in] db the MDBX_db record containing the stats to return.
 * [out] arg the address of an MDBX_stat structure to receive the stats.
 * Returns 0, this function always succeeds. */
static int __cold mdbx_stat0(MDBX_env *env, MDBX_db *db, MDBX_stat *arg) {
  arg->ms_psize = env->me_psize;
  arg->ms_depth = db->md_depth;
  arg->ms_branch_pages = db->md_branch_pages;
  arg->ms_leaf_pages = db->md_leaf_pages;
  arg->ms_overflow_pages = db->md_overflow_pages;
  arg->ms_entries = db->md_entries;
  return MDBX_SUCCESS;
}

int __cold mdbx_env_stat(MDBX_env *env, MDBX_stat *arg, size_t bytes) {
  MDBX_meta *meta;

  if (unlikely(env == NULL || arg == NULL))
    return MDBX_EINVAL;
  if (unlikely(bytes != sizeof(MDBX_stat)))
    return MDBX_EINVAL;

  meta = mdbx_meta_head(env);
  return mdbx_stat0(env, &meta->mm_dbs[MAIN_DBI], arg);
}

int __cold mdbx_env_info(MDBX_env *env, MDBX_envinfo *arg, size_t bytes) {

  if (unlikely(env == NULL || arg == NULL))
    return MDBX_EINVAL;

  if (bytes != sizeof(MDBX_envinfo))
    return MDBX_EINVAL;

  const MDBX_meta *const meta0 = METAPAGE(env, 0);
  const MDBX_meta *const meta1 = METAPAGE(env, 1);
  const MDBX_meta *const meta2 = METAPAGE(env, 2);
  const MDBX_meta *meta;
  do {
    meta = mdbx_meta_head(env);
    arg->mi_recent_txnid = mdbx_meta_txnid_fluid(env, meta);
    arg->mi_meta0_txnid = mdbx_meta_txnid_fluid(env, meta0);
    arg->mi_meta0_sign = meta0->mm_datasync_sign;
    arg->mi_meta1_txnid = mdbx_meta_txnid_fluid(env, meta1);
    arg->mi_meta1_sign = meta1->mm_datasync_sign;
    arg->mi_meta2_txnid = mdbx_meta_txnid_fluid(env, meta2);
    arg->mi_meta2_sign = meta2->mm_datasync_sign;
    arg->mi_last_pgno = meta->mm_geo.next - 1;
    arg->mi_geo.lower = pgno2bytes(env, meta->mm_geo.lower);
    arg->mi_geo.upper = pgno2bytes(env, meta->mm_geo.upper);
    arg->mi_geo.current = pgno2bytes(env, meta->mm_geo.now);
    arg->mi_geo.shrink = pgno2bytes(env, meta->mm_geo.shrink);
    arg->mi_geo.grow = pgno2bytes(env, meta->mm_geo.grow);
    arg->mi_mapsize = env->me_mapsize;
    mdbx_compiler_barrier();
  } while (unlikely(arg->mi_meta0_txnid != mdbx_meta_txnid_fluid(env, meta0) ||
                    arg->mi_meta0_sign != meta0->mm_datasync_sign ||
                    arg->mi_meta1_txnid != mdbx_meta_txnid_fluid(env, meta1) ||
                    arg->mi_meta1_sign != meta1->mm_datasync_sign ||
                    arg->mi_meta2_txnid != mdbx_meta_txnid_fluid(env, meta2) ||
                    arg->mi_meta2_sign != meta2->mm_datasync_sign ||
                    meta != mdbx_meta_head(env) ||
                    arg->mi_recent_txnid != mdbx_meta_txnid_fluid(env, meta)));

  arg->mi_maxreaders = env->me_maxreaders;
  arg->mi_numreaders = env->me_lck ? env->me_lck->mti_numreaders : INT32_MAX;
  arg->mi_dxb_pagesize = env->me_psize;
  arg->mi_sys_pagesize = env->me_os_psize;

  arg->mi_latter_reader_txnid = 0;
  if (env->me_lck) {
    MDBX_reader *r = env->me_lck->mti_readers;
    arg->mi_latter_reader_txnid = arg->mi_recent_txnid;
    for (unsigned i = 0; i < arg->mi_numreaders; ++i) {
      if (r[i].mr_pid) {
        const txnid_t txnid = r[i].mr_txnid;
        if (arg->mi_latter_reader_txnid > txnid)
          arg->mi_latter_reader_txnid = txnid;
      }
    }
  }

  return MDBX_SUCCESS;
}

static MDBX_cmp_func *mdbx_default_keycmp(unsigned flags) {
  return (flags & MDBX_REVERSEKEY) ? mdbx_cmp_memnr : (flags & MDBX_INTEGERKEY)
                                                          ? mdbx_cmp_int_a2
                                                          : mdbx_cmp_memn;
}

static MDBX_cmp_func *mdbx_default_datacmp(unsigned flags) {
  return !(flags & MDBX_DUPSORT)
             ? 0
             : ((flags & MDBX_INTEGERDUP)
                    ? mdbx_cmp_int_ua
                    : ((flags & MDBX_REVERSEDUP) ? mdbx_cmp_memnr
                                                 : mdbx_cmp_memn));
}

static int mdbx_dbi_bind(MDBX_txn *txn, const MDBX_dbi dbi, unsigned user_flags,
                         MDBX_cmp_func *keycmp, MDBX_cmp_func *datacmp) {
  /* LY: so, accepting only three cases for the table's flags:
   * 1) user_flags and both comparators are zero
   *    = assume that a by-default mode/flags is requested for reading;
   * 2) user_flags exactly the same
   *    = assume that the target mode/flags are requested properly;
   * 3) user_flags differs, but table is empty and MDBX_CREATE is provided
   *    = assume that a properly create request with custom flags;
   */
  if ((user_flags ^ txn->mt_dbs[dbi].md_flags) & PERSISTENT_FLAGS) {
    /* flags ara differs, check other conditions */
    if (!user_flags && (!keycmp || keycmp == txn->mt_dbxs[dbi].md_cmp) &&
        (!datacmp || datacmp == txn->mt_dbxs[dbi].md_dcmp)) {
      /* no comparators were provided and flags are zero,
       * seems that is case #1 above */
      user_flags = txn->mt_dbs[dbi].md_flags;
    } else if ((user_flags & MDBX_CREATE) && txn->mt_dbs[dbi].md_entries == 0) {
      if (txn->mt_flags & MDBX_TXN_RDONLY)
        return /* FIXME: return extended info */ MDBX_EACCESS;
      /* make sure flags changes get committed */
      txn->mt_dbs[dbi].md_flags = user_flags & PERSISTENT_FLAGS;
      txn->mt_flags |= MDBX_TXN_DIRTY;
    } else {
      return /* FIXME: return extended info */ MDBX_INCOMPATIBLE;
    }
  }

  if (!txn->mt_dbxs[dbi].md_cmp || MDBX_DEBUG) {
    if (!keycmp)
      keycmp = mdbx_default_keycmp(user_flags);
    assert(!txn->mt_dbxs[dbi].md_cmp || txn->mt_dbxs[dbi].md_cmp == keycmp);
    txn->mt_dbxs[dbi].md_cmp = keycmp;
  }

  if (!txn->mt_dbxs[dbi].md_dcmp || MDBX_DEBUG) {
    if (!datacmp)
      datacmp = mdbx_default_datacmp(user_flags);
    assert(!txn->mt_dbxs[dbi].md_dcmp || txn->mt_dbxs[dbi].md_dcmp == datacmp);
    txn->mt_dbxs[dbi].md_dcmp = datacmp;
  }

  return MDBX_SUCCESS;
}

int mdbx_dbi_open_ex(MDBX_txn *txn, const char *table_name, unsigned user_flags,
                     MDBX_dbi *dbi, MDBX_cmp_func *keycmp,
                     MDBX_cmp_func *datacmp) {
  if (unlikely(!txn || !dbi || (user_flags & ~VALID_FLAGS) != 0))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(txn->mt_flags & MDBX_TXN_BLOCKED))
    return MDBX_BAD_TXN;

  /* main table? */
  if (!table_name) {
    *dbi = MAIN_DBI;
    return mdbx_dbi_bind(txn, MAIN_DBI, user_flags, keycmp, datacmp);
  }

  if (txn->mt_dbxs[MAIN_DBI].md_cmp == NULL) {
    txn->mt_dbxs[MAIN_DBI].md_cmp =
        mdbx_default_keycmp(txn->mt_dbs[MAIN_DBI].md_flags);
    txn->mt_dbxs[MAIN_DBI].md_dcmp =
        mdbx_default_datacmp(txn->mt_dbs[MAIN_DBI].md_flags);
  }

  /* Is the DB already open? */
  size_t len = strlen(table_name);
  MDBX_dbi scan, slot = txn->mt_numdbs;
  for (scan = txn->mt_numdbs; --scan >= CORE_DBS;) {
    if (!txn->mt_dbxs[scan].md_name.iov_len) {
      /* Remember this free slot */
      slot = scan;
      continue;
    }
    if (len == txn->mt_dbxs[scan].md_name.iov_len &&
        !strncmp(table_name, txn->mt_dbxs[scan].md_name.iov_base, len)) {
      *dbi = scan;
      return mdbx_dbi_bind(txn, scan, user_flags, keycmp, datacmp);
    }
  }

  /* Fail, if no free slot and max hit */
  MDBX_env *env = txn->mt_env;
  if (unlikely(slot >= env->me_maxdbs))
    return MDBX_DBS_FULL;

  /* Cannot mix named table with some main-table flags */
  if (unlikely(txn->mt_dbs[MAIN_DBI].md_flags &
               (MDBX_DUPSORT | MDBX_INTEGERKEY)))
    return (user_flags & MDBX_CREATE) ? MDBX_INCOMPATIBLE : MDBX_NOTFOUND;

  /* Find the DB info */
  int exact = 0;
  MDBX_val key, data;
  key.iov_len = len;
  key.iov_base = (void *)table_name;
  MDBX_cursor mc;
  mdbx_cursor_init(&mc, txn, MAIN_DBI, NULL);
  int rc = mdbx_cursor_set(&mc, &key, &data, MDBX_SET, &exact);
  if (unlikely(rc != MDBX_SUCCESS)) {
    if (rc != MDBX_NOTFOUND || !(user_flags & MDBX_CREATE))
      return rc;
  } else {
    /* make sure this is actually a table */
    MDBX_node *node = NODEPTR(mc.mc_pg[mc.mc_top], mc.mc_ki[mc.mc_top]);
    if (unlikely((node->mn_flags & (F_DUPDATA | F_SUBDATA)) != F_SUBDATA))
      return MDBX_INCOMPATIBLE;
  }

  /* Done here so we cannot fail after creating a new DB */
  char *namedup = mdbx_strdup(table_name);
  if (unlikely(!namedup))
    return MDBX_ENOMEM;

  int err = mdbx_fastmutex_acquire(&env->me_dbi_lock);
  if (unlikely(err != MDBX_SUCCESS)) {
    free(namedup);
    return err;
  }

  unsigned dbflag = DB_NEW | DB_VALID | DB_USRVALID;
  if (unlikely(rc)) {
    /* MDBX_NOTFOUND and MDBX_CREATE: Create new DB */
    assert(rc == MDBX_NOTFOUND);
    MDBX_db db_dummy;
    memset(&db_dummy, 0, sizeof(db_dummy));
    db_dummy.md_root = P_INVALID;
    db_dummy.md_flags = user_flags & PERSISTENT_FLAGS;
    data.iov_len = sizeof(db_dummy);
    data.iov_base = &db_dummy;
    WITH_CURSOR_TRACKING(
        mc,
        rc = mdbx_cursor_put(&mc, &key, &data, F_SUBDATA | MDBX_NOOVERWRITE));

    if (unlikely(rc != MDBX_SUCCESS))
      goto bailout;

    dbflag |= DB_DIRTY;
  }

  /* Got info, register DBI in this txn */
  txn->mt_dbxs[slot].md_name.iov_base = namedup;
  txn->mt_dbxs[slot].md_name.iov_len = len;
  txn->mt_dbxs[slot].md_cmp = nullptr;
  txn->mt_dbxs[slot].md_dcmp = nullptr;
  txn->mt_dbflags[slot] = (uint8_t)dbflag;
  txn->mt_dbiseqs[slot] = (env->me_dbiseqs[slot] += 1);

  txn->mt_dbs[slot] = *(MDBX_db *)data.iov_base;
  rc = mdbx_dbi_bind(txn, slot, user_flags, keycmp, datacmp);
  if (unlikely(rc != MDBX_SUCCESS)) {
    assert((dbflag & DB_DIRTY) == 0);
    /* cleanup slot */
    txn->mt_dbxs[slot].md_name.iov_base = NULL;
    txn->mt_dbxs[slot].md_name.iov_len = 0;
    txn->mt_dbflags[slot] = 0;
  bailout:
    free(namedup);
  } else {
    *dbi = slot;
    if (slot == txn->mt_numdbs)
      txn->mt_numdbs++;
  }

  mdbx_ensure(env, mdbx_fastmutex_release(&env->me_dbi_lock) == MDBX_SUCCESS);
  return rc;
}

int mdbx_dbi_open(MDBX_txn *txn, const char *table_name, unsigned table_flags,
                  MDBX_dbi *dbi) {
  return mdbx_dbi_open_ex(txn, table_name, table_flags, dbi, nullptr, nullptr);
}

int __cold mdbx_dbi_stat(MDBX_txn *txn, MDBX_dbi dbi, MDBX_stat *arg,
                         size_t bytes) {
  if (unlikely(!arg || !txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_VALID)))
    return MDBX_EINVAL;

  if (unlikely(bytes != sizeof(MDBX_stat)))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_flags & MDBX_TXN_BLOCKED))
    return MDBX_BAD_TXN;

  if (unlikely(txn->mt_dbflags[dbi] & DB_STALE)) {
    MDBX_cursor mc;
    MDBX_xcursor mx;
    /* Stale, must read the DB's root. cursor_init does it for us. */
    mdbx_cursor_init(&mc, txn, dbi, &mx);
  }
  return mdbx_stat0(txn->mt_env, &txn->mt_dbs[dbi], arg);
}

static int mdbx_dbi_close_locked(MDBX_env *env, MDBX_dbi dbi) {
  if (unlikely(dbi < CORE_DBS || dbi >= env->me_maxdbs))
    return MDBX_EINVAL;

  char *ptr = env->me_dbxs[dbi].md_name.iov_base;
  /* If there was no name, this was already closed */
  if (unlikely(!ptr))
    return MDBX_BAD_DBI;

  env->me_dbxs[dbi].md_name.iov_base = NULL;
  env->me_dbxs[dbi].md_name.iov_len = 0;
  env->me_dbflags[dbi] = 0;
  env->me_dbiseqs[dbi]++;
  free(ptr);
  return MDBX_SUCCESS;
}

int mdbx_dbi_close(MDBX_env *env, MDBX_dbi dbi) {
  if (unlikely(dbi < CORE_DBS || dbi >= env->me_maxdbs))
    return MDBX_EINVAL;

  int rc = mdbx_fastmutex_acquire(&env->me_dbi_lock);
  if (likely(rc == MDBX_SUCCESS)) {
    rc = mdbx_dbi_close_locked(env, dbi);
    mdbx_ensure(env, mdbx_fastmutex_release(&env->me_dbi_lock) == MDBX_SUCCESS);
  }
  return rc;
}

int mdbx_dbi_flags_ex(MDBX_txn *txn, MDBX_dbi dbi, unsigned *flags,
                      unsigned *state) {
  if (unlikely(!txn || !flags || !state))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_VALID)))
    return MDBX_EINVAL;

  *flags = txn->mt_dbs[dbi].md_flags & PERSISTENT_FLAGS;
  *state = txn->mt_dbflags[dbi] & (DB_NEW | DB_DIRTY | DB_STALE);

  return MDBX_SUCCESS;
}

int mdbx_dbi_flags(MDBX_txn *txn, MDBX_dbi dbi, unsigned *flags) {
  unsigned state;
  return mdbx_dbi_flags_ex(txn, dbi, flags, &state);
}

/* Add all the DB's pages to the free list.
 * [in] mc Cursor on the DB to free.
 * [in] subs non-Zero to check for sub-DBs in this DB.
 * Returns 0 on success, non-zero on failure. */
static int mdbx_drop0(MDBX_cursor *mc, int subs) {
  int rc;

  rc = mdbx_page_search(mc, NULL, MDBX_PS_FIRST);
  if (likely(rc == MDBX_SUCCESS)) {
    MDBX_txn *txn = mc->mc_txn;
    MDBX_node *ni;
    MDBX_cursor mx;
    unsigned i;

    /* DUPSORT sub-DBs have no ovpages/DBs. Omit scanning leaves.
     * This also avoids any P_LEAF2 pages, which have no nodes.
     * Also if the DB doesn't have sub-DBs and has no overflow
     * pages, omit scanning leaves. */
    if ((mc->mc_flags & C_SUB) || (!subs && !mc->mc_db->md_overflow_pages))
      mdbx_cursor_pop(mc);

    mdbx_cursor_copy(mc, &mx);
    while (mc->mc_snum > 0) {
      MDBX_page *mp = mc->mc_pg[mc->mc_top];
      unsigned n = NUMKEYS(mp);
      if (IS_LEAF(mp)) {
        for (i = 0; i < n; i++) {
          ni = NODEPTR(mp, i);
          if (ni->mn_flags & F_BIGDATA) {
            MDBX_page *omp;
            pgno_t pg;
            memcpy(&pg, NODEDATA(ni), sizeof(pg));
            rc = mdbx_page_get(mc, pg, &omp, NULL);
            if (unlikely(rc))
              goto done;
            mdbx_cassert(mc, IS_OVERFLOW(omp));
            rc =
                mdbx_pnl_append_range(&txn->mt_befree_pages, pg, omp->mp_pages);
            if (unlikely(rc))
              goto done;
            mc->mc_db->md_overflow_pages -= omp->mp_pages;
            if (!mc->mc_db->md_overflow_pages && !subs)
              break;
          } else if (subs && (ni->mn_flags & F_SUBDATA)) {
            mdbx_xcursor_init1(mc, ni);
            rc = mdbx_drop0(&mc->mc_xcursor->mx_cursor, 0);
            if (unlikely(rc))
              goto done;
          }
        }
        if (!subs && !mc->mc_db->md_overflow_pages)
          goto pop;
      } else {
        if (unlikely((rc = mdbx_pnl_need(&txn->mt_befree_pages, n)) != 0))
          goto done;
        for (i = 0; i < n; i++) {
          pgno_t pg;
          ni = NODEPTR(mp, i);
          pg = NODEPGNO(ni);
          /* free it */
          mdbx_pnl_xappend(txn->mt_befree_pages, pg);
        }
      }
      if (!mc->mc_top)
        break;
      mdbx_cassert(mc, i <= UINT16_MAX);
      mc->mc_ki[mc->mc_top] = (indx_t)i;
      rc = mdbx_cursor_sibling(mc, 1);
      if (rc) {
        if (unlikely(rc != MDBX_NOTFOUND))
          goto done;
      /* no more siblings, go back to beginning
       * of previous level. */
      pop:
        mdbx_cursor_pop(mc);
        mc->mc_ki[0] = 0;
        for (i = 1; i < mc->mc_snum; i++) {
          mc->mc_ki[i] = 0;
          mc->mc_pg[i] = mx.mc_pg[i];
        }
      }
    }
    /* free it */
    rc = mdbx_pnl_append(&txn->mt_befree_pages, mc->mc_db->md_root);
  done:
    if (unlikely(rc))
      txn->mt_flags |= MDBX_TXN_ERROR;
  } else if (rc == MDBX_NOTFOUND) {
    rc = MDBX_SUCCESS;
  }
  mc->mc_flags &= ~C_INITIALIZED;
  return rc;
}

int mdbx_drop(MDBX_txn *txn, MDBX_dbi dbi, int del) {
  if (unlikely(1 < (unsigned)del || !txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_USRVALID)))
    return MDBX_EINVAL;

  if (unlikely(TXN_DBI_CHANGED(txn, dbi)))
    return MDBX_BAD_DBI;

  if (unlikely(F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY)))
    return MDBX_EACCESS;

  MDBX_cursor *mc;
  int rc = mdbx_cursor_open(txn, dbi, &mc);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;

  MDBX_env *env = txn->mt_env;
  rc = mdbx_fastmutex_acquire(&env->me_dbi_lock);
  if (unlikely(rc != MDBX_SUCCESS)) {
    mdbx_cursor_close(mc);
    return rc;
  }

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_USRVALID))) {
    rc = MDBX_EINVAL;
    goto bailout;
  }

  if (unlikely(TXN_DBI_CHANGED(txn, dbi))) {
    rc = MDBX_BAD_DBI;
    goto bailout;
  }

  rc = mdbx_drop0(mc, mc->mc_db->md_flags & MDBX_DUPSORT);
  /* Invalidate the dropped DB's cursors */
  for (MDBX_cursor *m2 = txn->mt_cursors[dbi]; m2; m2 = m2->mc_next)
    m2->mc_flags &= ~(C_INITIALIZED | C_EOF);
  if (unlikely(rc))
    goto bailout;

  /* Can't delete the main DB */
  if (del && dbi >= CORE_DBS) {
    rc = mdbx_del0(txn, MAIN_DBI, &mc->mc_dbx->md_name, NULL, F_SUBDATA);
    if (likely(!rc)) {
      txn->mt_dbflags[dbi] = DB_STALE;
      mdbx_dbi_close_locked(env, dbi);
    } else {
      txn->mt_flags |= MDBX_TXN_ERROR;
    }
  } else {
    /* reset the DB record, mark it dirty */
    txn->mt_dbflags[dbi] |= DB_DIRTY;
    txn->mt_dbs[dbi].md_depth = 0;
    txn->mt_dbs[dbi].md_branch_pages = 0;
    txn->mt_dbs[dbi].md_leaf_pages = 0;
    txn->mt_dbs[dbi].md_overflow_pages = 0;
    txn->mt_dbs[dbi].md_entries = 0;
    txn->mt_dbs[dbi].md_root = P_INVALID;
    txn->mt_dbs[dbi].md_seq = 0;

    txn->mt_flags |= MDBX_TXN_DIRTY;
  }

bailout:
  mdbx_cursor_close(mc);
  mdbx_ensure(env, mdbx_fastmutex_release(&env->me_dbi_lock) == MDBX_SUCCESS);
  return rc;
}

int mdbx_set_compare(MDBX_txn *txn, MDBX_dbi dbi, MDBX_cmp_func *cmp) {
  if (unlikely(!txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_USRVALID)))
    return MDBX_EINVAL;

  txn->mt_dbxs[dbi].md_cmp = cmp;
  return MDBX_SUCCESS;
}

int mdbx_set_dupsort(MDBX_txn *txn, MDBX_dbi dbi, MDBX_cmp_func *cmp) {
  if (unlikely(!txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_USRVALID)))
    return MDBX_EINVAL;

  txn->mt_dbxs[dbi].md_dcmp = cmp;
  return MDBX_SUCCESS;
}

int __cold mdbx_reader_list(MDBX_env *env, MDBX_msg_func *func, void *ctx) {
  char buf[64];
  int rc = 0, first = 1;

  if (unlikely(!env || !func))
    return -MDBX_EINVAL;

  if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
    return MDBX_EBADSIGN;

  const MDBX_lockinfo *const lck = env->me_lck;
  const unsigned snap_nreaders = lck->mti_numreaders;
  for (unsigned i = 0; i < snap_nreaders; i++) {
    if (lck->mti_readers[i].mr_pid) {
      const txnid_t txnid = lck->mti_readers[i].mr_txnid;
      if (txnid == ~(txnid_t)0)
        snprintf(buf, sizeof(buf), "%10" PRIuPTR " %" PRIxPTR " -\n",
                 (uintptr_t)lck->mti_readers[i].mr_pid,
                 (uintptr_t)lck->mti_readers[i].mr_tid);
      else
        snprintf(buf, sizeof(buf), "%10" PRIuPTR " %" PRIxPTR " %" PRIaTXN "\n",
                 (uintptr_t)lck->mti_readers[i].mr_pid,
                 (uintptr_t)lck->mti_readers[i].mr_tid, txnid);

      if (first) {
        first = 0;
        rc = func("    pid     thread     txnid\n", ctx);
        if (rc < 0)
          break;
      }
      rc = func(buf, ctx);
      if (rc < 0)
        break;
    }
  }
  if (first)
    rc = func("(no active readers)\n", ctx);

  return rc;
}

/* Insert pid into list if not already present.
 * return -1 if already present. */
static int __cold mdbx_pid_insert(mdbx_pid_t *ids, mdbx_pid_t pid) {
  /* binary search of pid in list */
  unsigned base = 0;
  unsigned cursor = 1;
  int val = 0;
  unsigned n = ids[0];

  while (n > 0) {
    unsigned pivot = n >> 1;
    cursor = base + pivot + 1;
    val = pid - ids[cursor];

    if (val < 0) {
      n = pivot;
    } else if (val > 0) {
      base = cursor;
      n -= pivot + 1;
    } else {
      /* found, so it's a duplicate */
      return -1;
    }
  }

  if (val > 0)
    ++cursor;

  ids[0]++;
  for (n = ids[0]; n > cursor; n--)
    ids[n] = ids[n - 1];
  ids[n] = pid;
  return 0;
}

int __cold mdbx_reader_check(MDBX_env *env, int *dead) {
  if (unlikely(!env || env->me_signature != MDBX_ME_SIGNATURE))
    return MDBX_EINVAL;
  if (dead)
    *dead = 0;
  return mdbx_reader_check0(env, false, dead);
}

/* Return:
 *  MDBX_RESULT_TRUE - done and mutex recovered
 *  MDBX_SUCCESS     - done
 *  Otherwise errcode. */
int __cold mdbx_reader_check0(MDBX_env *env, int rdt_locked, int *dead) {
  assert(rdt_locked >= 0);

  if (unlikely(env->me_pid != mdbx_getpid())) {
    env->me_flags |= MDBX_FATAL_ERROR;
    return MDBX_PANIC;
  }

  MDBX_lockinfo *const lck = env->me_lck;
  const unsigned snap_nreaders = lck->mti_numreaders;
  mdbx_pid_t *pids = alloca((snap_nreaders + 1) * sizeof(mdbx_pid_t));
  pids[0] = 0;

  int rc = MDBX_SUCCESS, count = 0;
  for (unsigned i = 0; i < snap_nreaders; i++) {
    const mdbx_pid_t pid = lck->mti_readers[i].mr_pid;
    if (pid == 0)
      continue /* skip empty */;
    if (pid == env->me_pid)
      continue /* skip self */;
    if (mdbx_pid_insert(pids, pid) != 0)
      continue /* such pid already processed */;

    int err = mdbx_rpid_check(env, pid);
    if (err == MDBX_RESULT_TRUE)
      continue /* reader is live */;

    if (err != MDBX_SUCCESS) {
      rc = err;
      break /* mdbx_rpid_check() failed */;
    }

    /* stale reader found */
    if (!rdt_locked) {
      err = mdbx_rdt_lock(env);
      if (MDBX_IS_ERROR(err)) {
        rc = err;
        break;
      }

      rdt_locked = -1;
      if (err == MDBX_RESULT_TRUE) {
        /* mutex recovered, the mdbx_mutex_failed() checked all readers */
        rc = MDBX_RESULT_TRUE;
        break;
      }

      /* a other process may have clean and reused slot, recheck */
      if (lck->mti_readers[i].mr_pid != pid)
        continue;

      err = mdbx_rpid_check(env, pid);
      if (MDBX_IS_ERROR(err)) {
        rc = err;
        break;
      }

      if (err != MDBX_SUCCESS)
        continue /* the race with other process, slot reused */;
    }

    /* clean it */
    for (unsigned j = i; j < snap_nreaders; j++) {
      if (lck->mti_readers[j].mr_pid == pid) {
        mdbx_debug("clear stale reader pid %" PRIuPTR " txn %" PRIaTXN "",
                   (size_t)pid, lck->mti_readers[j].mr_txnid);
        lck->mti_readers[j].mr_pid = 0;
        lck->mti_reader_finished_flag = true;
        count++;
      }
    }
  }

  if (rdt_locked < 0)
    mdbx_rdt_unlock(env);

  if (dead)
    *dead = count;
  return rc;
}

int __cold mdbx_setup_debug(int flags, MDBX_debug_func *logger) {
  unsigned ret = mdbx_runtime_flags;
  mdbx_runtime_flags = flags;

#ifdef __linux__
  if (flags & MDBX_DBG_DUMP) {
    int core_filter_fd = open("/proc/self/coredump_filter", O_TRUNC | O_RDWR);
    if (core_filter_fd >= 0) {
      char buf[32];
      const unsigned r = pread(core_filter_fd, buf, sizeof(buf), 0);
      if (r > 0 && r < sizeof(buf)) {
        buf[r] = 0;
        unsigned long mask = strtoul(buf, NULL, 16);
        if (mask != ULONG_MAX) {
          mask |= 1 << 3 /* Dump file-backed shared mappings */;
          mask |= 1 << 6 /* Dump shared huge pages */;
          mask |= 1 << 8 /* Dump shared DAX pages */;
          unsigned w = snprintf(buf, sizeof(buf), "0x%lx\n", mask);
          if (w > 0 && w < sizeof(buf)) {
            w = pwrite(core_filter_fd, buf, w, 0);
            (void)w;
          }
        }
      }
      close(core_filter_fd);
    }
  }
#endif /* __linux__ */

  mdbx_debug_logger = logger;
  return ret;
}

static txnid_t __cold mdbx_oomkick(MDBX_env *env, const txnid_t laggard) {
  mdbx_debug("DB size maxed out");

  int retry;
  for (retry = 0; retry < INT_MAX; ++retry) {
    txnid_t oldest = mdbx_reclaiming_detent(env);
    mdbx_assert(env, oldest < env->me_txn0->mt_txnid);
    mdbx_assert(env, oldest >= laggard);
    mdbx_assert(env, oldest >= env->me_oldest[0]);
    if (oldest == laggard)
      return oldest;

    if (MDBX_IS_ERROR(mdbx_reader_check0(env, false, NULL)))
      break;

    MDBX_reader *const rtbl = env->me_lck->mti_readers;
    MDBX_reader *asleep = nullptr;
    for (int i = env->me_lck->mti_numreaders; --i >= 0;) {
      if (rtbl[i].mr_pid) {
        mdbx_jitter4testing(true);
        const txnid_t snap = rtbl[i].mr_txnid;
        if (oldest > snap && laggard <= /* ignore pending updates */ snap) {
          oldest = snap;
          asleep = &rtbl[i];
        }
      }
    }

    if (laggard < oldest || !asleep) {
      if (retry && env->me_oom_func) {
        /* LY: notify end of oom-loop */
        const txnid_t gap = oldest - laggard;
        env->me_oom_func(env, 0, 0, laggard,
                         (gap < UINT_MAX) ? (unsigned)gap : UINT_MAX, -retry);
      }
      mdbx_notice("oom-kick: update oldest %" PRIaTXN " -> %" PRIaTXN,
                  env->me_oldest[0], oldest);
      mdbx_assert(env, env->me_oldest[0] <= oldest);
      return env->me_oldest[0] = oldest;
    }

    mdbx_tid_t tid;
    mdbx_pid_t pid;
    int rc;

    if (!env->me_oom_func)
      break;

    pid = asleep->mr_pid;
    tid = asleep->mr_tid;
    if (asleep->mr_txnid != laggard || pid <= 0)
      continue;

    const txnid_t gap =
        mdbx_meta_txnid_stable(env, mdbx_meta_head(env)) - laggard;
    rc = env->me_oom_func(env, pid, tid, laggard,
                          (gap < UINT_MAX) ? (unsigned)gap : UINT_MAX, retry);
    if (rc < 0)
      break;

    if (rc) {
      asleep->mr_txnid = ~(txnid_t)0;
      env->me_lck->mti_reader_finished_flag = true;
      if (rc > 1) {
        asleep->mr_tid = 0;
        asleep->mr_pid = 0;
        mdbx_coherent_barrier();
      }
    }
  }

  if (retry && env->me_oom_func) {
    /* LY: notify end of oom-loop */
    env->me_oom_func(env, 0, 0, laggard, 0, -retry);
  }
  return mdbx_find_oldest(env->me_txn);
}

int __cold mdbx_env_set_syncbytes(MDBX_env *env, size_t bytes) {
  if (unlikely(!env))
    return MDBX_EINVAL;

  if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
    return MDBX_EBADSIGN;

  env->me_sync_threshold = bytes;
  return env->me_map ? mdbx_env_sync(env, 0) : MDBX_SUCCESS;
}

int __cold mdbx_env_set_oomfunc(MDBX_env *env, MDBX_oom_func *oomfunc) {
  if (unlikely(!env))
    return MDBX_EINVAL;

  if (unlikely(env->me_signature != MDBX_ME_SIGNATURE))
    return MDBX_EBADSIGN;

  env->me_oom_func = oomfunc;
  return MDBX_SUCCESS;
}

MDBX_oom_func *__cold mdbx_env_get_oomfunc(MDBX_env *env) {
  return likely(env && env->me_signature == MDBX_ME_SIGNATURE)
             ? env->me_oom_func
             : NULL;
}

#ifdef __SANITIZE_THREAD__
/* LY: avoid tsan-trap by me_txn, mm_last_pg and mt_next_pgno */
__attribute__((no_sanitize_thread, noinline))
#endif
int mdbx_txn_straggler(MDBX_txn *txn, int *percent)
{
  if (unlikely(!txn))
    return -MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  MDBX_env *env = txn->mt_env;
  if (unlikely((txn->mt_flags & MDBX_RDONLY) == 0)) {
    *percent =
        (int)((txn->mt_next_pgno * UINT64_C(100) + txn->mt_end_pgno / 2) /
              txn->mt_end_pgno);
    return -1;
  }

  txnid_t recent;
  MDBX_meta *meta;
  do {
    meta = mdbx_meta_head(env);
    recent = mdbx_meta_txnid_fluid(env, meta);
    if (percent) {
      const pgno_t maxpg = meta->mm_geo.now;
      *percent = (int)((meta->mm_geo.next * UINT64_C(100) + maxpg / 2) / maxpg);
    }
  } while (unlikely(recent != mdbx_meta_txnid_fluid(env, meta)));

  txnid_t lag = recent - txn->mt_ro_reader->mr_txnid;
  return (lag > INT_MAX) ? INT_MAX : (int)lag;
}

typedef struct mdbx_walk_ctx {
  MDBX_txn *mw_txn;
  void *mw_user;
  MDBX_pgvisitor_func *mw_visitor;
} mdbx_walk_ctx_t;

/* Depth-first tree traversal. */
static int __cold mdbx_env_walk(mdbx_walk_ctx_t *ctx, const char *dbi,
                                pgno_t pg, int deep) {
  MDBX_page *mp;
  int rc, i, nkeys;
  size_t header_size, unused_size, payload_size, align_bytes;
  const char *type;

  if (pg == P_INVALID)
    return MDBX_SUCCESS; /* empty db */

  MDBX_cursor mc;
  memset(&mc, 0, sizeof(mc));
  mc.mc_snum = 1;
  mc.mc_txn = ctx->mw_txn;

  rc = mdbx_page_get(&mc, pg, &mp, NULL);
  if (rc)
    return rc;
  if (pg != mp->mp_pgno)
    return MDBX_CORRUPTED;

  nkeys = NUMKEYS(mp);
  header_size = IS_LEAF2(mp) ? PAGEHDRSZ : PAGEHDRSZ + mp->mp_lower;
  unused_size = SIZELEFT(mp);
  payload_size = 0;

  /* LY: Don't use mask here, e.g bitwise
   * (P_BRANCH|P_LEAF|P_LEAF2|P_META|P_OVERFLOW|P_SUBP).
   * Pages should not me marked dirty/loose or otherwise. */
  switch (mp->mp_flags) {
  case P_BRANCH:
    type = "branch";
    if (nkeys < 1)
      return MDBX_CORRUPTED;
    break;
  case P_LEAF:
    type = "leaf";
    break;
  case P_LEAF | P_SUBP:
    type = "dupsort-subleaf";
    break;
  case P_LEAF | P_LEAF2:
    type = "dupfixed-leaf";
    break;
  case P_LEAF | P_LEAF2 | P_SUBP:
    type = "dupsort-dupfixed-subleaf";
    break;
  case P_META:
  case P_OVERFLOW:
  default:
    return MDBX_CORRUPTED;
  }

  for (align_bytes = i = 0; i < nkeys;
       align_bytes += ((payload_size + align_bytes) & 1), i++) {
    MDBX_node *node;

    if (IS_LEAF2(mp)) {
      /* LEAF2 pages have no mp_ptrs[] or node headers */
      payload_size += mp->mp_leaf2_ksize;
      continue;
    }

    node = NODEPTR(mp, i);
    payload_size += NODESIZE + node->mn_ksize;

    if (IS_BRANCH(mp)) {
      rc = mdbx_env_walk(ctx, dbi, NODEPGNO(node), deep);
      if (rc)
        return rc;
      continue;
    }

    assert(IS_LEAF(mp));
    if (node->mn_flags & F_BIGDATA) {
      MDBX_page *omp;
      pgno_t *opg;
      size_t over_header, over_payload, over_unused;

      payload_size += sizeof(pgno_t);
      opg = NODEDATA(node);
      rc = mdbx_page_get(&mc, *opg, &omp, NULL);
      if (rc)
        return rc;
      if (*opg != omp->mp_pgno)
        return MDBX_CORRUPTED;
      /* LY: Don't use mask here, e.g bitwise
       * (P_BRANCH|P_LEAF|P_LEAF2|P_META|P_OVERFLOW|P_SUBP).
       * Pages should not me marked dirty/loose or otherwise. */
      if (P_OVERFLOW != omp->mp_flags)
        return MDBX_CORRUPTED;

      over_header = PAGEHDRSZ;
      over_payload = NODEDSZ(node);
      over_unused = pgno2bytes(ctx->mw_txn->mt_env, omp->mp_pages) -
                    over_payload - over_header;

      rc = ctx->mw_visitor(*opg, omp->mp_pages, ctx->mw_user, dbi,
                           "overflow-data", 1, over_payload, over_header,
                           over_unused);
      if (rc)
        return rc;
      continue;
    }

    payload_size += NODEDSZ(node);
    if (node->mn_flags & F_SUBDATA) {
      MDBX_db *db = NODEDATA(node);
      char *name = NULL;

      if (!(node->mn_flags & F_DUPDATA)) {
        name = NODEKEY(node);
        ptrdiff_t namelen = (char *)db - name;
        name = memcpy(alloca(namelen + 1), name, namelen);
        name[namelen] = 0;
      }
      rc = mdbx_env_walk(ctx, (name && name[0]) ? name : dbi, db->md_root,
                         deep + 1);
      if (rc)
        return rc;
    }
  }

  return ctx->mw_visitor(mp->mp_pgno, 1, ctx->mw_user, dbi, type, nkeys,
                         payload_size, header_size, unused_size + align_bytes);
}

int __cold mdbx_env_pgwalk(MDBX_txn *txn, MDBX_pgvisitor_func *visitor,
                           void *user) {
  if (unlikely(!txn))
    return MDBX_BAD_TXN;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  mdbx_walk_ctx_t ctx;
  ctx.mw_txn = txn;
  ctx.mw_user = user;
  ctx.mw_visitor = visitor;

  int rc = visitor(0, NUM_METAS, user, "meta", "meta", NUM_METAS,
                   sizeof(MDBX_meta) * NUM_METAS, PAGEHDRSZ * NUM_METAS,
                   (txn->mt_env->me_psize - sizeof(MDBX_meta) - PAGEHDRSZ) *
                       NUM_METAS);
  if (!rc)
    rc = mdbx_env_walk(&ctx, "free", txn->mt_dbs[FREE_DBI].md_root, 0);
  if (!rc)
    rc = mdbx_env_walk(&ctx, "main", txn->mt_dbs[MAIN_DBI].md_root, 0);
  if (!rc)
    rc = visitor(P_INVALID, 0, user, NULL, NULL, 0, 0, 0, 0);
  return rc;
}

int mdbx_canary_put(MDBX_txn *txn, const mdbx_canary *canary) {
  if (unlikely(!txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(txn->mt_flags & MDBX_TXN_BLOCKED))
    return MDBX_BAD_TXN;

  if (unlikely(F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY)))
    return MDBX_EACCESS;

  if (likely(canary)) {
    if (txn->mt_canary.x == canary->x && txn->mt_canary.y == canary->y &&
        txn->mt_canary.z == canary->z)
      return MDBX_SUCCESS;
    txn->mt_canary.x = canary->x;
    txn->mt_canary.y = canary->y;
    txn->mt_canary.z = canary->z;
  }
  txn->mt_canary.v = txn->mt_txnid;

  if ((txn->mt_flags & MDBX_TXN_DIRTY) == 0) {
    MDBX_env *env = txn->mt_env;
    txn->mt_flags |= MDBX_TXN_DIRTY;
    env->me_sync_pending += env->me_psize;
  }

  return MDBX_SUCCESS;
}

int mdbx_canary_get(MDBX_txn *txn, mdbx_canary *canary) {
  if (unlikely(txn == NULL || canary == NULL))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  *canary = txn->mt_canary;
  return MDBX_SUCCESS;
}

int mdbx_cursor_on_first(MDBX_cursor *mc) {
  if (unlikely(mc == NULL))
    return MDBX_EINVAL;

  if (unlikely(mc->mc_signature != MDBX_MC_SIGNATURE))
    return MDBX_EBADSIGN;

  if (!(mc->mc_flags & C_INITIALIZED))
    return MDBX_RESULT_FALSE;

  for (unsigned i = 0; i < mc->mc_snum; ++i) {
    if (mc->mc_ki[i])
      return MDBX_RESULT_FALSE;
  }

  return MDBX_RESULT_TRUE;
}

int mdbx_cursor_on_last(MDBX_cursor *mc) {
  if (unlikely(mc == NULL))
    return MDBX_EINVAL;

  if (unlikely(mc->mc_signature != MDBX_MC_SIGNATURE))
    return MDBX_EBADSIGN;

  if (!(mc->mc_flags & C_INITIALIZED))
    return MDBX_RESULT_FALSE;

  for (unsigned i = 0; i < mc->mc_snum; ++i) {
    unsigned nkeys = NUMKEYS(mc->mc_pg[i]);
    if (mc->mc_ki[i] < nkeys - 1)
      return MDBX_RESULT_FALSE;
  }

  return MDBX_RESULT_TRUE;
}

int mdbx_cursor_eof(MDBX_cursor *mc) {
  if (unlikely(mc == NULL))
    return MDBX_EINVAL;

  if (unlikely(mc->mc_signature != MDBX_MC_SIGNATURE))
    return MDBX_EBADSIGN;

  if ((mc->mc_flags & C_INITIALIZED) == 0)
    return MDBX_RESULT_TRUE;

  if (mc->mc_snum == 0)
    return MDBX_RESULT_TRUE;

  if ((mc->mc_flags & C_EOF) &&
      mc->mc_ki[mc->mc_top] >= NUMKEYS(mc->mc_pg[mc->mc_top]))
    return MDBX_RESULT_TRUE;

  return MDBX_RESULT_FALSE;
}

static int mdbx_is_samedata(const MDBX_val *a, const MDBX_val *b) {
  return a->iov_len == b->iov_len &&
         memcmp(a->iov_base, b->iov_base, a->iov_len) == 0;
}

/* Позволяет обновить или удалить существующую запись с получением
 * в old_data предыдущего значения данных. При этом если new_data равен
 * нулю, то выполняется удаление, иначе обновление/вставка.
 *
 * Текущее значение может находиться в уже измененной (грязной) странице.
 * В этом случае страница будет перезаписана при обновлении, а само старое
 * значение утрачено. Поэтому исходно в old_data должен быть передан
 * дополнительный буфер для копирования старого значения.
 * Если переданный буфер слишком мал, то функция вернет -1, установив
 * old_data->iov_len в соответствующее значение.
 *
 * Для не-уникальных ключей также возможен второй сценарий использования,
 * когда посредством old_data из записей с одинаковым ключом для
 * удаления/обновления выбирается конкретная. Для выбора этого сценария
 * во flags следует одновременно указать MDBX_CURRENT и MDBX_NOOVERWRITE.
 * Именно эта комбинация выбрана, так как она лишена смысла, и этим позволяет
 * идентифицировать запрос такого сценария.
 *
 * Функция может быть замещена соответствующими операциями с курсорами
 * после двух доработок (TODO):
 *  - внешняя аллокация курсоров, в том числе на стеке (без malloc).
 *  - получения статуса страницы по адресу (знать о P_DIRTY).
 */
int mdbx_replace(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *new_data,
                 MDBX_val *old_data, unsigned flags) {
  if (unlikely(!key || !old_data || !txn || old_data == new_data))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(old_data->iov_base == NULL && old_data->iov_len))
    return MDBX_EINVAL;

  if (unlikely(new_data == NULL && !(flags & MDBX_CURRENT)))
    return MDBX_EINVAL;

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_USRVALID)))
    return MDBX_EINVAL;

  if (unlikely(flags &
               ~(MDBX_NOOVERWRITE | MDBX_NODUPDATA | MDBX_RESERVE |
                 MDBX_APPEND | MDBX_APPENDDUP | MDBX_CURRENT)))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_flags & (MDBX_TXN_RDONLY | MDBX_TXN_BLOCKED)))
    return (txn->mt_flags & MDBX_TXN_RDONLY) ? MDBX_EACCESS : MDBX_BAD_TXN;

  MDBX_cursor mc;
  MDBX_xcursor mx;
  mdbx_cursor_init(&mc, txn, dbi, &mx);
  mc.mc_next = txn->mt_cursors[dbi];
  txn->mt_cursors[dbi] = &mc;

  int rc;
  MDBX_val present_key = *key;
  if (F_ISSET(flags, MDBX_CURRENT | MDBX_NOOVERWRITE)) {
    /* в old_data значение для выбора конкретного дубликата */
    if (unlikely(!(txn->mt_dbs[dbi].md_flags & MDBX_DUPSORT))) {
      rc = MDBX_EINVAL;
      goto bailout;
    }

    /* убираем лишний бит, он был признаком запрошенного режима */
    flags -= MDBX_NOOVERWRITE;

    rc = mdbx_cursor_get(&mc, &present_key, old_data, MDBX_GET_BOTH);
    if (rc != MDBX_SUCCESS)
      goto bailout;

    if (new_data) {
      /* обновление конкретного дубликата */
      if (mdbx_is_samedata(old_data, new_data))
        /* если данные совпадают, то ничего делать не надо */
        goto bailout;
    }
  } else {
    /* в old_data буфер для сохранения предыдущего значения */
    if (unlikely(new_data && old_data->iov_base == new_data->iov_base))
      return MDBX_EINVAL;
    MDBX_val present_data;
    rc = mdbx_cursor_get(&mc, &present_key, &present_data, MDBX_SET_KEY);
    if (unlikely(rc != MDBX_SUCCESS)) {
      old_data->iov_base = NULL;
      old_data->iov_len = rc;
      if (rc != MDBX_NOTFOUND || (flags & MDBX_CURRENT))
        goto bailout;
    } else if (flags & MDBX_NOOVERWRITE) {
      rc = MDBX_KEYEXIST;
      *old_data = present_data;
      goto bailout;
    } else {
      MDBX_page *page = mc.mc_pg[mc.mc_top];
      if (txn->mt_dbs[dbi].md_flags & MDBX_DUPSORT) {
        if (flags & MDBX_CURRENT) {
          /* для не-уникальных ключей позволяем update/delete только если ключ
           * один */
          MDBX_node *leaf = NODEPTR(page, mc.mc_ki[mc.mc_top]);
          if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
            mdbx_tassert(txn, XCURSOR_INITED(&mc) &&
                                  mc.mc_xcursor->mx_db.md_entries > 1);
            if (mc.mc_xcursor->mx_db.md_entries > 1) {
              rc = MDBX_EMULTIVAL;
              goto bailout;
            }
          }
          /* если данные совпадают, то ничего делать не надо */
          if (new_data && mdbx_is_samedata(&present_data, new_data)) {
            *old_data = *new_data;
            goto bailout;
          }
          /* В оригинальной LMDB фладок MDBX_CURRENT здесь приведет
           * к замене данных без учета MDBX_DUPSORT сортировки,
           * но здесь это в любом случае допустимо, так как мы
           * проверили что для ключа есть только одно значение. */
        } else if ((flags & MDBX_NODUPDATA) &&
                   mdbx_is_samedata(&present_data, new_data)) {
          /* если данные совпадают и установлен MDBX_NODUPDATA */
          rc = MDBX_KEYEXIST;
          goto bailout;
        }
      } else {
        /* если данные совпадают, то ничего делать не надо */
        if (new_data && mdbx_is_samedata(&present_data, new_data)) {
          *old_data = *new_data;
          goto bailout;
        }
        flags |= MDBX_CURRENT;
      }

      if (page->mp_flags & P_DIRTY) {
        if (unlikely(old_data->iov_len < present_data.iov_len)) {
          old_data->iov_base = NULL;
          old_data->iov_len = present_data.iov_len;
          rc = MDBX_RESULT_TRUE;
          goto bailout;
        }
        memcpy(old_data->iov_base, present_data.iov_base, present_data.iov_len);
        old_data->iov_len = present_data.iov_len;
      } else {
        *old_data = present_data;
      }
    }
  }

  if (likely(new_data))
    rc = mdbx_cursor_put(&mc, key, new_data, flags);
  else
    rc = mdbx_cursor_del(&mc, 0);

bailout:
  txn->mt_cursors[dbi] = mc.mc_next;
  return rc;
}

int mdbx_get_ex(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
                size_t *values_count) {
  DKBUF;
  mdbx_debug("===> get db %u key [%s]", dbi, DKEY(key));

  if (unlikely(!key || !data || !txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_USRVALID)))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_flags & MDBX_TXN_BLOCKED))
    return MDBX_BAD_TXN;

  MDBX_cursor mc;
  MDBX_xcursor mx;
  mdbx_cursor_init(&mc, txn, dbi, &mx);

  int exact = 0;
  int rc = mdbx_cursor_set(&mc, key, data, MDBX_SET_KEY, &exact);
  if (unlikely(rc != MDBX_SUCCESS)) {
    if (rc == MDBX_NOTFOUND && values_count)
      *values_count = 0;
    return rc;
  }

  if (values_count) {
    *values_count = 1;
    if (mc.mc_xcursor != NULL) {
      MDBX_node *leaf = NODEPTR(mc.mc_pg[mc.mc_top], mc.mc_ki[mc.mc_top]);
      if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
        mdbx_tassert(txn, mc.mc_xcursor == &mx &&
                              (mx.mx_cursor.mc_flags & C_INITIALIZED));
        *values_count = (sizeof(*values_count) >= sizeof(mx.mx_db.md_entries) ||
                         mx.mx_db.md_entries <= SIZE_MAX)
                            ? (size_t)mx.mx_db.md_entries
                            : SIZE_MAX;
      }
    }
  }
  return MDBX_SUCCESS;
}

/* Функция сообщает находится ли указанный адрес в "грязной" странице у
 * заданной пишущей транзакции. В конечном счете это позволяет избавиться от
 * лишнего копирования данных из НЕ-грязных страниц.
 *
 * "Грязные" страницы - это те, которые уже были изменены в ходе пишущей
 * транзакции. Соответственно, какие-либо дальнейшие изменения могут привести
 * к перезаписи таких страниц. Поэтому все функции, выполняющие изменения, в
 * качестве аргументов НЕ должны получать указатели на данные в таких
 * страницах. В свою очередь "НЕ грязные" страницы перед модификацией будут
 * скопированы.
 *
 * Другими словами, данные из "грязных" страниц должны быть либо скопированы
 * перед передачей в качестве аргументов для дальнейших модификаций, либо
 * отвергнуты на стадии проверки корректности аргументов.
 *
 * Таким образом, функция позволяет как избавится от лишнего копирования,
 * так и выполнить более полную проверку аргументов.
 *
 * ВАЖНО: Передаваемый указатель должен указывать на начало данных. Только
 * так гарантируется что актуальный заголовок страницы будет физически
 * расположен в той-же странице памяти, в том числе для многостраничных
 * P_OVERFLOW страниц с длинными данными. */
int mdbx_is_dirty(const MDBX_txn *txn, const void *ptr) {
  if (unlikely(!txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(txn->mt_flags & MDBX_TXN_RDONLY))
    return MDBX_RESULT_FALSE;

  const MDBX_env *env = txn->mt_env;
  const uintptr_t mask = ~(uintptr_t)(env->me_psize - 1);
  const MDBX_page *page = (const MDBX_page *)((uintptr_t)ptr & mask);

  /* LY: Тут не всё хорошо с абсолютной достоверностью результата,
   * так как флажок P_DIRTY в LMDB может означать не совсем то,
   * что было исходно задумано, детали см в логике кода mdbx_page_touch().
   *
   * Более того, в режиме БЕЗ WRITEMAP грязные страницы выделяются через
   * malloc(), т.е. находятся вне mmap-диапазона и тогда чтобы отличить
   * действительно грязную страницу от указателя на данные пользователя
   * следует сканировать dirtylist, что накладно.
   *
   * Тем не менее, однозначно страница "не грязная" (не будет переписана
   * во время транзакции) если адрес находится внутри mmap-диапазона
   * и в заголовке страницы нет флажка P_DIRTY. */
  if (env->me_map < (uint8_t *)page) {
    const size_t usedbytes = pgno2bytes(env, txn->mt_next_pgno);
    if ((uint8_t *)page < env->me_map + usedbytes) {
      /* страница внутри диапазона, смотрим на флажки */
      return (page->mp_flags & (P_DIRTY | P_LOOSE | P_KEEP))
                 ? MDBX_RESULT_TRUE
                 : MDBX_RESULT_FALSE;
    }
    /* Гипотетически здесь возможна ситуация, когда указатель адресует что-то
     * в пределах mmap, но за границей распределенных страниц. Это тяжелая
     * ошибка, к которой не возможно прийти без каких-то больших нарушений.
     * Поэтому не проверяем этот случай кроме как assert-ом, на то что
     * страница вне mmap-диаппазона. */
    mdbx_tassert(txn, (uint8_t *)page >= env->me_map + env->me_mapsize);
  }

  /* Страница вне используемого mmap-диапазона, т.е. либо в функцию был
   * передан некорректный адрес, либо адрес в теневой странице, которая была
   * выделена посредством malloc().
   *
   * Для WRITE_MAP режима такая страница однозначно "не грязная",
   * а для режимов без WRITE_MAP следует просматривать списки dirty
   * и spilled страниц у каких-либо транзакций (в том числе дочерних).
   *
   * Поэтому для WRITE_MAP возвращаем false, а для остальных режимов
   * всегда true. Такая логика имеет ряд преимуществ:
   *  - не тратим время на просмотр списков;
   *  - результат всегда безопасен (может быть ложно-положительным,
   *    но не ложно-отрицательным);
   *  - результат не зависит от вложенности транзакций и от относительного
   *    положения переданной транзакции в этой рекурсии. */
  return (env->me_flags & MDBX_WRITEMAP) ? MDBX_RESULT_FALSE : MDBX_RESULT_TRUE;
}

int mdbx_dbi_sequence(MDBX_txn *txn, MDBX_dbi dbi, uint64_t *result,
                      uint64_t increment) {
  if (unlikely(!txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_EBADSIGN;

  if (unlikely(txn->mt_owner != mdbx_thread_self()))
    return MDBX_THREAD_MISMATCH;

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_USRVALID)))
    return MDBX_EINVAL;

  if (unlikely(TXN_DBI_CHANGED(txn, dbi)))
    return MDBX_BAD_DBI;

  MDBX_db *dbs = &txn->mt_dbs[dbi];
  if (likely(result))
    *result = dbs->md_seq;

  if (likely(increment > 0)) {
    if (unlikely(txn->mt_flags & MDBX_TXN_BLOCKED))
      return MDBX_BAD_TXN;

    if (unlikely(F_ISSET(txn->mt_flags, MDBX_TXN_RDONLY)))
      return MDBX_EACCESS;

    uint64_t new = dbs->md_seq + increment;
    if (unlikely(new < increment))
      return MDBX_RESULT_TRUE;

    assert(new > dbs->md_seq);
    dbs->md_seq = new;
    txn->mt_flags |= MDBX_TXN_DIRTY;
    txn->mt_dbflags[dbi] |= DB_DIRTY;
  }

  return MDBX_SUCCESS;
}

/*----------------------------------------------------------------------------*/
/* attribute support functions for Nexenta */

static __inline int mdbx_attr_peek(MDBX_val *data, mdbx_attr_t *attrptr) {
  if (unlikely(data->iov_len < sizeof(mdbx_attr_t)))
    return MDBX_INCOMPATIBLE;

  if (likely(attrptr != NULL))
    *attrptr = *(mdbx_attr_t *)data->iov_base;
  data->iov_len -= sizeof(mdbx_attr_t);
  data->iov_base =
      likely(data->iov_len > 0) ? ((mdbx_attr_t *)data->iov_base) + 1 : NULL;

  return MDBX_SUCCESS;
}

static __inline int mdbx_attr_poke(MDBX_val *reserved, MDBX_val *data,
                                   mdbx_attr_t attr, unsigned flags) {
  mdbx_attr_t *space = reserved->iov_base;
  if (flags & MDBX_RESERVE) {
    if (likely(data != NULL)) {
      data->iov_base = data->iov_len ? space + 1 : NULL;
    }
  } else {
    *space = attr;
    if (likely(data != NULL)) {
      memcpy(space + 1, data->iov_base, data->iov_len);
    }
  }

  return MDBX_SUCCESS;
}

int mdbx_cursor_get_attr(MDBX_cursor *mc, MDBX_val *key, MDBX_val *data,
                         mdbx_attr_t *attrptr, MDBX_cursor_op op) {
  int rc = mdbx_cursor_get(mc, key, data, op);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;

  return mdbx_attr_peek(data, attrptr);
}

int mdbx_get_attr(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
                  uint64_t *attrptr) {
  int rc = mdbx_get(txn, dbi, key, data);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;

  return mdbx_attr_peek(data, attrptr);
}

int mdbx_put_attr(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
                  mdbx_attr_t attr, unsigned flags) {
  MDBX_val reserve;
  reserve.iov_base = NULL;
  reserve.iov_len = (data ? data->iov_len : 0) + sizeof(mdbx_attr_t);

  int rc = mdbx_put(txn, dbi, key, &reserve, flags | MDBX_RESERVE);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;

  return mdbx_attr_poke(&reserve, data, attr, flags);
}

int mdbx_cursor_put_attr(MDBX_cursor *cursor, MDBX_val *key, MDBX_val *data,
                         mdbx_attr_t attr, unsigned flags) {
  MDBX_val reserve;
  reserve.iov_base = NULL;
  reserve.iov_len = (data ? data->iov_len : 0) + sizeof(mdbx_attr_t);

  int rc = mdbx_cursor_put(cursor, key, &reserve, flags | MDBX_RESERVE);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;

  return mdbx_attr_poke(&reserve, data, attr, flags);
}

int mdbx_set_attr(MDBX_txn *txn, MDBX_dbi dbi, MDBX_val *key, MDBX_val *data,
                  mdbx_attr_t attr) {
  if (unlikely(!key || !txn))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE))
    return MDBX_VERSION_MISMATCH;

  if (unlikely(!TXN_DBI_EXIST(txn, dbi, DB_USRVALID)))
    return MDBX_EINVAL;

  if (unlikely(txn->mt_flags & (MDBX_TXN_RDONLY | MDBX_TXN_BLOCKED)))
    return (txn->mt_flags & MDBX_TXN_RDONLY) ? MDBX_EACCESS : MDBX_BAD_TXN;

  MDBX_cursor mc;
  MDBX_xcursor mx;
  MDBX_val old_data;
  mdbx_cursor_init(&mc, txn, dbi, &mx);
  int rc = mdbx_cursor_set(&mc, key, &old_data, MDBX_SET, NULL);
  if (unlikely(rc != MDBX_SUCCESS)) {
    if (rc == MDBX_NOTFOUND && data) {
      mc.mc_next = txn->mt_cursors[dbi];
      txn->mt_cursors[dbi] = &mc;
      rc = mdbx_cursor_put_attr(&mc, key, data, attr, 0);
      txn->mt_cursors[dbi] = mc.mc_next;
    }
    return rc;
  }

  mdbx_attr_t old_attr = 0;
  rc = mdbx_attr_peek(&old_data, &old_attr);
  if (unlikely(rc != MDBX_SUCCESS))
    return rc;

  if (old_attr == attr && (!data || (data->iov_len == old_data.iov_len &&
                                     memcmp(data->iov_base, old_data.iov_base,
                                            old_data.iov_len) == 0)))
    return MDBX_SUCCESS;

  mc.mc_next = txn->mt_cursors[dbi];
  txn->mt_cursors[dbi] = &mc;
  rc = mdbx_cursor_put_attr(&mc, key, data ? data : &old_data, attr,
                            MDBX_CURRENT);
  txn->mt_cursors[dbi] = mc.mc_next;
  return rc;
}

//----------------------------------------------------------------------------

#ifdef __SANITIZE_ADDRESS__
LIBMDBX_API __attribute__((weak)) const char *__asan_default_options() {
  return "symbolize=1:allow_addr2line=1:"
#ifdef _DEBUG
         "debug=1:"
#endif /* _DEBUG */
         "report_globals=1:"
         "replace_str=1:replace_intrin=1:"
         "malloc_context_size=9:"
         "detect_leaks=1:"
         "check_printf=1:"
         "detect_deadlocks=1:"
#ifndef LTO_ENABLED
         "check_initialization_order=1:"
#endif
         "detect_stack_use_after_return=1:"
         "intercept_tls_get_addr=1:"
         "decorate_proc_maps=1:"
         "abort_on_error=1";
}
#endif /* __SANITIZE_ADDRESS__ */