libmdbx/mdb.c

/** @file mdb.c
 *	@brief Lightning memory-mapped database library
 *
 *	A Btree-based database management library modeled loosely on the
 *	BerkeleyDB API, but much simplified.
 */
/*
 * Copyright 2011-2016 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>.
 *
 * This code is derived from btree.c written by Martin Hedenfalk.
 *
 * 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.
 */

#ifndef MDB_DEBUG
#	define MDB_DEBUG 0
#endif

#include "./reopen.h"
#include "./barriers.h"

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/param.h>
#include <sys/uio.h>
#include <sys/mman.h>
#ifdef HAVE_SYS_FILE_H
#	include <sys/file.h>
#endif
#include <fcntl.h>

#include <errno.h>
#include <limits.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <alloca.h>
#include <pthread.h>

#if !(defined(BYTE_ORDER) || defined(__BYTE_ORDER))
#	include <netinet/in.h>
#	include <resolv.h>	/* defines BYTE_ORDER on HPUX and Solaris */
#endif

#ifndef _POSIX_SYNCHRONIZED_IO
#	define fdatasync fsync
#endif

#ifndef BYTE_ORDER
#	if (defined(_LITTLE_ENDIAN) || defined(_BIG_ENDIAN)) && !(defined(_LITTLE_ENDIAN) && defined(_BIG_ENDIAN))
		/* Solaris just defines one or the other */
#		define LITTLE_ENDIAN	1234
#		define BIG_ENDIAN	4321
#		ifdef _LITTLE_ENDIAN
#			define BYTE_ORDER	LITTLE_ENDIAN
#		else
#			define BYTE_ORDER	BIG_ENDIAN
#		endif
#	else
#		define BYTE_ORDER	__BYTE_ORDER
#	endif
#endif

#ifndef LITTLE_ENDIAN
#	define LITTLE_ENDIAN	__LITTLE_ENDIAN
#endif
#ifndef BIG_ENDIAN
#	define BIG_ENDIAN	__BIG_ENDIAN
#endif

#if defined(__i386) || defined(__x86_64) || defined(_M_IX86)
#	define MISALIGNED_OK	1
#endif

#include "./lmdb.h"
#include "./midl.h"

#if ! MDBX_MODE_ENABLED
#	define MDB_COALESCE		0
#	define MDB_LIFORECLAIM	0
#	define MDB_DBG_ASSERT	0
#	define MDB_DBG_PRINT	0
#	define MDB_DBG_TRACE	0
#	define MDB_DBG_EXTRA	0
#	define MDB_DBG_AUDIT	0
#	define MDB_DBG_EDGE		0
#endif /* ! MDBX_MODE_ENABLED */

#if (BYTE_ORDER == LITTLE_ENDIAN) == (BYTE_ORDER == BIG_ENDIAN)
#	error "Unknown or unsupported endianness (BYTE_ORDER)"
#elif (-6 & 5) || CHAR_BIT != 8 || UINT_MAX < 0xffffffff || ULONG_MAX % 0xFFFF
#	error "Two's complement, reasonably sized integer types, please"
#endif

/** @defgroup internal	LMDB Internals
 *	@{
 */
/** @defgroup compat	Compatibility Macros
 *	A bunch of macros to minimize the amount of platform-specific ifdefs
 *	needed throughout the rest of the code. When the features this library
 *	needs are similar enough to POSIX to be hidden in a one-or-two line
 *	replacement, this macro approach is used.
 *	@{
 */

	/** Features under development */
#ifndef MDB_DEVEL
#	define MDB_DEVEL 0
#endif

	/** Wrapper around __func__, which is a C99 feature */
#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
#	define mdb_func_	__func__
#elif (defined(__GNUC__) && __GNUC__ >= 2) || defined(__clang__)
#	define mdb_func_	__FUNCTION__
#else
	/* If a debug message says <mdb_unknown>(), update the #if statements above */
#	define mdb_func_	"<mdb_unknown>"
#endif

/** Some platforms define the EOWNERDEAD error code
 * even though they don't support Robust Mutexes.
 * Compile with -DMDB_USE_ROBUST=0.
 */
#ifndef MDB_USE_ROBUST
	/* Howard Chu: Android currently lacks Robust Mutex support */
#	if defined(EOWNERDEAD) && !defined(ANDROID) \
	/* LY: glibc before 2.10 has a troubles with Robust Mutex too.
	 * But more over:
	 *  - we couldn't test code with glibc < 2.12;
	 *  - we won't provide compatibility with old systems. */ \
	&& !(defined(__GLIBC__) && ((__GLIBC__ << 16)|__GLIBC_MINOR__) < 0x02000c)
#		define MDB_USE_ROBUST	1
#	else
#		define MDB_USE_ROBUST	0
#	endif
#endif /* MDB_USE_ROBUST */

/* Internal error codes, not exposed outside liblmdb */
#define	MDB_NO_ROOT		(MDB_LAST_ERRCODE + 10)

	/** Mutex for the reader table (rw = r) or write transaction (rw = w).
	 */
#define MDB_MUTEX(env, rw) \
		(&(env)->me_txns->mti_##rw##mutex)

	/** An abstraction for a file handle.
	 *	On POSIX systems file handles are small integers. On Windows
	 *	they're opaque pointers.
	 */
#define	HANDLE	int

	/**	A value for an invalid file handle.
	 *	Mainly used to initialize file variables and signify that they are
	 *	unused.
	 */
#define INVALID_HANDLE_VALUE	(-1)

	/** Get the size of a memory page for the system.
	 *	This is the basic size that the platform's memory manager uses, and is
	 *	fundamental to the use of memory-mapped files.
	 */
#define	GET_PAGESIZE(x)	((x) = sysconf(_SC_PAGE_SIZE))

/** @} */

static int mdb_mutex_lock(MDB_env *env, pthread_mutex_t *mutex);
static int mdb_mutex_failed(MDB_env *env, pthread_mutex_t *mutex, int rc);
static void mdb_mutex_unlock(MDB_env *env, pthread_mutex_t *mutex);

	/** A page number in the database.
	 *	Note that 64 bit page numbers are overkill, since pages themselves
	 *	already represent 12-13 bits of addressable memory, and the OS will
	 *	always limit applications to a maximum of 63 bits of address space.
	 *
	 *	@note In the #MDB_node structure, we only store 48 bits of this value,
	 *	which thus limits us to only 60 bits of addressable data.
	 */
typedef MDB_ID	pgno_t;

	/** A transaction ID.
	 *	See struct MDB_txn.mt_txnid for details.
	 */
typedef MDB_ID	txnid_t;

/** @defgroup debug	Debug Macros
 *	@{
 */
	/** Debuging output value of a cursor DBI: Negative in a sub-cursor. */
#define DDBI(mc) \
	(((mc)->mc_flags & C_SUB) ? -(int)(mc)->mc_dbi : (int)(mc)->mc_dbi)
/** @} */

	/**	@brief The maximum size of a database page.
	 *
	 *	It is 32k or 64k, since value-PAGEBASE must fit in
	 *	#MDB_page.%mp_upper.
	 *
	 *	LMDB will use database pages < OS pages if needed.
	 *	That causes more I/O in write transactions: The OS must
	 *	know (read) the whole page before writing a partial page.
	 *
	 *	Note that we don't currently support Huge pages. On Linux,
	 *	regular data files cannot use Huge pages, and in general
	 *	Huge pages aren't actually pageable. We rely on the OS
	 *	demand-pager to read our data and page it out when memory
	 *	pressure from other processes is high. So until OSs have
	 *	actual paging support for Huge pages, they're not viable.
	 */
#define MAX_PAGESIZE	 (PAGEBASE ? 0x10000 : 0x8000)

	/** The minimum number of keys required in a database page.
	 *	Setting this to a larger value will place a smaller bound on the
	 *	maximum size of a data item. Data items larger than this size will
	 *	be pushed into overflow pages instead of being stored directly in
	 *	the B-tree node. This value used to default to 4. With a page size
	 *	of 4096 bytes that meant that any item larger than 1024 bytes would
	 *	go into an overflow page. That also meant that on average 2-3KB of
	 *	each overflow page was wasted space. The value cannot be lower than
	 *	2 because then there would no longer be a tree structure. With this
	 *	value, items larger than 2KB will go into overflow pages, and on
	 *	average only 1KB will be wasted.
	 */
#define MDB_MINKEYS	 2

	/**	A stamp that identifies a file as an LMDB file.
	 *	There's nothing special about this value other than that it is easily
	 *	recognizable, and it will reflect any byte order mismatches.
	 */
#define MDB_MAGIC	 0xBEEFC0DE

	/**	The version number for a database's datafile format. */
#define MDB_DATA_VERSION	 ((MDB_DEVEL) ? 999 : 1)
	/**	The version number for a database's lockfile format. */
#define MDB_LOCK_VERSION	 ((MDB_DEVEL) ? 999 : 1)

	/**	@brief The max size of a key we can write, or 0 for computed max.
	 *
	 *	This macro should normally be left alone or set to 0.
	 *	Note that a database with big keys or dupsort data cannot be
	 *	reliably modified by a liblmdb which uses a smaller max.
	 *	The default is 511 for backwards compat, or 0 when #MDB_DEVEL.
	 *
	 *	Other values are allowed, for backwards compat.  However:
	 *	A value bigger than the computed max can break if you do not
	 *	know what you are doing, and liblmdb <= 0.9.10 can break when
	 *	modifying a DB with keys/dupsort data bigger than its max.
	 *
	 *	Data items in an #MDB_DUPSORT database are also limited to
	 *	this size, since they're actually keys of a sub-DB.  Keys and
	 *	#MDB_DUPSORT data items must fit on a node in a regular page.
	 */
#ifndef MDB_MAXKEYSIZE
#	define MDB_MAXKEYSIZE	 ((MDB_DEVEL) ? 0 : 511)
#endif

	/**	The maximum size of a key we can write to the environment. */
#if MDB_MAXKEYSIZE
#	define ENV_MAXKEY(env)	(MDB_MAXKEYSIZE)
#else
#	define ENV_MAXKEY(env)	((env)->me_maxkey_limit)
#endif /* MDB_MAXKEYSIZE */

	/**	@brief The maximum size of a data item.
	 *
	 *	We only store a 32 bit value for node sizes.
	 */
#define MAXDATASIZE	0xffffffffUL

	/**	Key size which fits in a #DKBUF.
	 *	@ingroup debug
	 */
#define DKBUF_MAXKEYSIZE ((MDB_MAXKEYSIZE) > 0 ? (MDB_MAXKEYSIZE) : 511)
	/**	A key buffer.
	 *	@ingroup debug
	 *	This is used for printing a hex dump of a key's contents.
	 */
#define DKBUF char kbuf[DKBUF_MAXKEYSIZE*2+1]
	/**	Display a key in hex.
	 *	@ingroup debug
	 *	Invoke a function to display a key in hex.
	 */
#define	DKEY(x)	mdb_dkey(x, kbuf)

	/** An invalid page number.
	 *	Mainly used to denote an empty tree.
	 */
#define P_INVALID	 (~(pgno_t)0)

	/** Test if the flags \b f are set in a flag word \b w. */
#define F_ISSET(w, f)	 (((w) & (f)) == (f))

	/** Round \b n up to an even number. */
#define EVEN(n)		(((n) + 1U) & -2) /* sign-extending -2 to match n+1U */

	/**	Used for offsets within a single page.
	 *	Since memory pages are typically 4 or 8KB in size, 12-13 bits,
	 *	this is plenty.
	 */
typedef uint16_t	 indx_t;

	/**	Default size of memory map.
	 *	This is certainly too small for any actual applications. Apps should always set
	 *	the size explicitly using #mdb_env_set_mapsize().
	 */
#define DEFAULT_MAPSIZE	1048576

/**	@defgroup readers	Reader Lock Table
 *	Readers don't acquire any locks for their data access. Instead, they
 *	simply record their transaction ID in the reader table. The reader
 *	mutex is needed just to find an empty slot in the reader table. The
 *	slot's address is saved in thread-specific data so that subsequent read
 *	transactions started by the same thread need no further locking to proceed.
 *
 *	If #MDB_NOTLS is set, the slot address is not saved in thread-specific data.
 *
 *	No reader table is used if the database is on a read-only filesystem, or
 *	if #MDB_NOLOCK is set.
 *
 *	Since the database uses multi-version concurrency control, readers don't
 *	actually need any locking. This table is used to keep track of which
 *	readers are using data from which old transactions, so that we'll know
 *	when a particular old transaction is no longer in use. Old transactions
 *	that have discarded any data pages can then have those pages reclaimed
 *	for use by a later write transaction.
 *
 *	The lock table is constructed such that reader slots are aligned with the
 *	processor's cache line size. Any slot is only ever used by one thread.
 *	This alignment guarantees that there will be no contention or cache
 *	thrashing as threads update their own slot info, and also eliminates
 *	any need for locking when accessing a slot.
 *
 *	A writer thread will scan every slot in the table to determine the oldest
 *	outstanding reader transaction. Any freed pages older than this will be
 *	reclaimed by the writer. The writer doesn't use any locks when scanning
 *	this table. This means that there's no guarantee that the writer will
 *	see the most up-to-date reader info, but that's not required for correct
 *	operation - all we need is to know the upper bound on the oldest reader,
 *	we don't care at all about the newest reader. So the only consequence of
 *	reading stale information here is that old pages might hang around a
 *	while longer before being reclaimed. That's actually good anyway, because
 *	the longer we delay reclaiming old pages, the more likely it is that a
 *	string of contiguous pages can be found after coalescing old pages from
 *	many old transactions together.
 *	@{
 */
	/**	Number of slots in the reader table.
	 *	This value was chosen somewhat arbitrarily. 126 readers plus a
	 *	couple mutexes fit exactly into 8KB on my development machine.
	 *	Applications should set the table size using #mdb_env_set_maxreaders().
	 */
#define DEFAULT_READERS	126

	/**	The information we store in a single slot of the reader table.
	 *	In addition to a transaction ID, we also record the process and
	 *	thread ID that owns a slot, so that we can detect stale information,
	 *	e.g. threads or processes that went away without cleaning up.
	 *	@note We currently don't check for stale records. We simply re-init
	 *	the table when we know that we're the only process opening the
	 *	lock file.
	 */
typedef struct MDB_rxbody {
	/**	Current Transaction ID when this transaction began, or (txnid_t)-1.
	 *	Multiple readers that start at the same time will probably have the
	 *	same ID here. Again, it's not important to exclude them from
	 *	anything; all we need to know is which version of the DB they
	 *	started from so we can avoid overwriting any data used in that
	 *	particular version.
	 */
	volatile txnid_t		mrb_txnid;
	/** The process ID of the process owning this reader txn. */
	volatile pid_t	mrb_pid;
	/** The thread ID of the thread owning this txn. */
	volatile pthread_t	mrb_tid;
	/** Pointer to the context for deferred cleanup reader thread. */
	struct MDB_rthc *mrb_rthc;
} MDB_rxbody;

	/** The actual reader record, with cacheline padding. */
typedef struct MDB_reader {
	union {
		MDB_rxbody mrx;
		/** shorthand for mrb_txnid */
#define	mr_txnid	mru.mrx.mrb_txnid
#define	mr_pid	mru.mrx.mrb_pid
#define	mr_tid	mru.mrx.mrb_tid
#define	mr_rthc	mru.mrx.mrb_rthc
		/** cache line alignment */
		char pad[(sizeof(MDB_rxbody)+CACHELINE_SIZE-1) & ~(CACHELINE_SIZE-1)];
	} mru;
} MDB_reader;

	/** The header for the reader table.
	 *	The table resides in a memory-mapped file. (This is a different file
	 *	than is used for the main database.)
	 *
	 *	For POSIX the actual mutexes reside in the shared memory of this
	 *	mapped file. On Windows, mutexes are named objects allocated by the
	 *	kernel; we store the mutex names in this mapped file so that other
	 *	processes can grab them. This same approach is also used on
	 *	MacOSX/Darwin (using named semaphores) since MacOSX doesn't support
	 *	process-shared POSIX mutexes. For these cases where a named object
	 *	is used, the object name is derived from a 64 bit FNV hash of the
	 *	environment pathname. As such, naming collisions are extremely
	 *	unlikely. If a collision occurs, the results are unpredictable.
	 */
typedef struct MDB_txbody {
		/** Stamp identifying this as an LMDB file. It must be set
		 *	to #MDB_MAGIC. */
	uint32_t	mtb_magic;
		/** Format of this lock file. Must be set to #MDB_LOCK_FORMAT. */
	uint32_t	mtb_format;
		/** Mutex protecting access to this table.
		 *	This is the #MDB_MUTEX(env,r) reader table lock.
		 */
	pthread_mutex_t	mtb_rmutex;
		/**	The ID of the last transaction committed to the database.
		 *	This is recorded here only for convenience; the value can always
		 *	be determined by reading the main database meta pages.
		 */
	volatile txnid_t		mtb_txnid;
		/** The number of slots that have been used in the reader table.
		 *	This always records the maximum count, it is not decremented
		 *	when readers release their slots.
		 */
	volatile unsigned	mtb_numreaders;
} MDB_txbody;

	/** The actual reader table definition. */
typedef struct MDB_txninfo {
	union {
		MDB_txbody mtb;
#define mti_magic	mt1.mtb.mtb_magic
#define mti_format	mt1.mtb.mtb_format
#define mti_rmutex	mt1.mtb.mtb_rmutex
#define mti_rmname	mt1.mtb.mtb_rmname
#define mti_txnid	mt1.mtb.mtb_txnid
#define mti_numreaders	mt1.mtb.mtb_numreaders
		char pad[(sizeof(MDB_txbody)+CACHELINE_SIZE-1) & ~(CACHELINE_SIZE-1)];
	} mt1;
	union {
		pthread_mutex_t	mt2_wmutex;
#	define mti_wmutex	mt2.mt2_wmutex
		char pad[(sizeof(pthread_mutex_t)+CACHELINE_SIZE-1) & ~(CACHELINE_SIZE-1)];
	} mt2;
	MDB_reader	mti_readers[1];
} MDB_txninfo;

	/** Lockfile format signature: version, features and field layout */
#define MDB_LOCK_FORMAT \
	((uint32_t) \
	 ((MDB_LOCK_VERSION) \
	  /* Flags which describe functionality */ \
	  + (0 /* SYSV_SEM_FLAG */ << 18) \
	  + (1 /* MDB_PIDLOCK */ << 16)))
/** @} */

/** Common header for all page types.
 * Overflow records occupy a number of contiguous pages with no
 * headers on any page after the first.
 */
typedef struct MDB_page {
#define	mp_pgno	mp_p.p_pgno
#define	mp_next	mp_p.p_next
	union {
		pgno_t		p_pgno;	/**< page number */
		struct MDB_page *p_next; /**< for in-memory list of freed pages */
	} mp_p;
	uint16_t	mp_ksize;
/**	@defgroup mdb_page	Page Flags
 *	@ingroup internal
 *	Flags for the page headers.
 *	@{
 */
#define	P_BRANCH	 0x01		/**< branch page */
#define	P_LEAF		 0x02		/**< leaf page */
#define	P_OVERFLOW	 0x04		/**< overflow page */
#define	P_META		 0x08		/**< meta page */
#define	P_DIRTY		 0x10		/**< dirty page, also set for #P_SUBP pages */
#define	P_LEAF2		 0x20		/**< for #MDB_DUPFIXED records */
#define	P_SUBP		 0x40		/**< for #MDB_DUPSORT sub-pages */
#define	P_LOOSE		 0x4000		/**< page was dirtied then freed, can be reused */
#define	P_KEEP		 0x8000		/**< leave this page alone during spill */
/** @} */
	uint16_t	mp_flags;		/**< @ref mdb_page */
#define mp_lower	mp_pb.pb.pb_lower
#define mp_upper	mp_pb.pb.pb_upper
#define mp_pages	mp_pb.pb_pages
	union {
		struct {
			indx_t		pb_lower;		/**< lower bound of free space */
			indx_t		pb_upper;		/**< upper bound of free space */
		} pb;
		uint32_t	pb_pages;	/**< number of overflow pages */
	} mp_pb;
	indx_t		mp_ptrs[1];		/**< dynamic size */
} MDB_page;

	/** Size of the page header, excluding dynamic data at the end */
#define PAGEHDRSZ	 ((unsigned) offsetof(MDB_page, mp_ptrs))

	/** Address of first usable data byte in a page, after the header */
#define PAGEDATA(p)	 ((void *)((char *)(p) + PAGEHDRSZ))

	/** ITS#7713, change PAGEBASE to handle 65536 byte pages */
#define	PAGEBASE	((MDB_DEVEL) ? PAGEHDRSZ : 0)

	/** Number of nodes on a page */
#define NUMKEYS(p)	 (((p)->mp_lower - (PAGEHDRSZ-PAGEBASE)) >> 1)

	/** The amount of space remaining in the page */
#define SIZELEFT(p)	 (indx_t)((p)->mp_upper - (p)->mp_lower)

	/** The percentage of space used in the page, in tenths of a percent. */
#define PAGEFILL(env, p) (1000L * ((env)->me_psize - PAGEHDRSZ - SIZELEFT(p)) / \
				((env)->me_psize - PAGEHDRSZ))
	/** The minimum page fill factor, in tenths of a percent.
	 *	Pages emptier than this are candidates for merging.
	 */
#define FILL_THRESHOLD	 250

	/** Test if a page is a leaf page */
#define IS_LEAF(p)	 F_ISSET((p)->mp_flags, P_LEAF)
	/** Test if a page is a LEAF2 page */
#define IS_LEAF2(p)	 F_ISSET((p)->mp_flags, P_LEAF2)
	/** Test if a page is a branch page */
#define IS_BRANCH(p)	 F_ISSET((p)->mp_flags, P_BRANCH)
	/** Test if a page is an overflow page */
#define IS_OVERFLOW(p)	 F_ISSET((p)->mp_flags, P_OVERFLOW)
	/** Test if a page is a sub page */
#define IS_SUBP(p)	 F_ISSET((p)->mp_flags, P_SUBP)

	/** The number of overflow pages needed to store the given size. */
#define OVPAGES(size, psize)	((PAGEHDRSZ-1 + (size)) / (psize) + 1)

	/** Link in #MDB_txn.%mt_loose_pgs list */
#define NEXT_LOOSE_PAGE(p)		(*(MDB_page **)((p) + 2))

	/** Header for a single key/data pair within a page.
	 * Used in pages of type #P_BRANCH and #P_LEAF without #P_LEAF2.
	 * We guarantee 2-byte alignment for 'MDB_node's.
	 */
typedef struct MDB_node {
	/** lo and hi are used for data size on leaf nodes and for
	 * child pgno on branch nodes. On 64 bit platforms, flags
	 * is also used for pgno. (Branch nodes have no flags).
	 * They are in host byte order in case that lets some
	 * accesses be optimized into a 32-bit word access.
	 */
#if BYTE_ORDER == LITTLE_ENDIAN
	unsigned short	mn_lo, mn_hi;	/**< part of data size or pgno */
#else
	unsigned short	mn_hi, mn_lo;
#endif
/** @defgroup mdb_node Node Flags
 *	@ingroup internal
 *	Flags for node headers.
 *	@{
 */
#define F_BIGDATA	 0x01			/**< data put on overflow page */
#define F_SUBDATA	 0x02			/**< data is a sub-database */
#define F_DUPDATA	 0x04			/**< data has duplicates */

/** valid flags for #mdb_node_add() */
#define	NODE_ADD_FLAGS	(F_DUPDATA|F_SUBDATA|MDB_RESERVE|MDB_APPEND)

/** @} */
	unsigned short	mn_flags;		/**< @ref mdb_node */
	unsigned short	mn_ksize;		/**< key size */
	char		mn_data[1];			/**< key and data are appended here */
} MDB_node;

	/** Size of the node header, excluding dynamic data at the end */
#define NODESIZE	 offsetof(MDB_node, mn_data)

	/** Bit position of top word in page number, for shifting mn_flags */
#define PGNO_TOPWORD ((pgno_t)-1 > 0xffffffffu ? 32 : 0)

	/** Size of a node in a branch page with a given key.
	 *	This is just the node header plus the key, there is no data.
	 */
#define INDXSIZE(k)	 (NODESIZE + ((k) == NULL ? 0 : (k)->mv_size))

	/** Size of a node in a leaf page with a given key and data.
	 *	This is node header plus key plus data size.
	 */
#define LEAFSIZE(k, d)	 (NODESIZE + (k)->mv_size + (d)->mv_size)

	/** Address of node \b i in page \b p */
#define NODEPTR(p, i)	 ((MDB_node *)((char *)(p) + (p)->mp_ptrs[i] + PAGEBASE))

	/** Address of the key for the node */
#define NODEKEY(node)	 (void *)((node)->mn_data)

	/** Address of the data for a node */
#define NODEDATA(node)	 (void *)((char *)(node)->mn_data + (node)->mn_ksize)

	/** Get the page number pointed to by a branch node */
#define NODEPGNO(node) \
	((node)->mn_lo | ((pgno_t) (node)->mn_hi << 16) | \
	 (PGNO_TOPWORD ? ((pgno_t) (node)->mn_flags << PGNO_TOPWORD) : 0))
	/** Set the page number in a branch node */
#define SETPGNO(node,pgno)	do { \
	(node)->mn_lo = (pgno) & 0xffff; (node)->mn_hi = (pgno) >> 16; \
	if (PGNO_TOPWORD) (node)->mn_flags = (pgno) >> PGNO_TOPWORD; } while(0)

	/** Get the size of the data in a leaf node */
#define NODEDSZ(node)	 ((node)->mn_lo | ((unsigned)(node)->mn_hi << 16))
	/** Set the size of the data for a leaf node */
#define SETDSZ(node,size)	do { \
	(node)->mn_lo = (size) & 0xffff; (node)->mn_hi = (size) >> 16;} while(0)
	/** The size of a key in a node */
#define NODEKSZ(node)	 ((node)->mn_ksize)

	/** Copy a page number from src to dst */
#ifdef MISALIGNED_OK
#	define COPY_PGNO(dst,src)	dst = src
#elif SIZE_MAX > 4294967295UL
#	define COPY_PGNO(dst,src)	do { \
		unsigned short *s, *d;	\
		s = (unsigned short *)&(src);	\
		d = (unsigned short *)&(dst);	\
		*d++ = *s++;	\
		*d++ = *s++;	\
		*d++ = *s++;	\
		*d = *s;	\
	} while (0)
#else
#	define COPY_PGNO(dst,src)	do { \
		unsigned short *s, *d;	\
		s = (unsigned short *)&(src);	\
		d = (unsigned short *)&(dst);	\
		*d++ = *s++;	\
		*d = *s;	\
	} while (0)
#endif /* MISALIGNED_OK */

/** The address of a key in a LEAF2 page.
	 *	LEAF2 pages are used for #MDB_DUPFIXED sorted-duplicate sub-DBs.
	 *	There are no node headers, keys are stored contiguously.
	 */
#define LEAF2KEY(p, i, ks)	((char *)(p) + PAGEHDRSZ + ((i)*(ks)))

	/** Set the \b node's key into \b keyptr, if requested. */
#define MDB_GET_KEY(node, keyptr)	{ if ((keyptr) != NULL) { \
	(keyptr)->mv_size = NODEKSZ(node); (keyptr)->mv_data = NODEKEY(node); } }

	/** Set the \b node's key into \b key. */
#define MDB_GET_KEY2(node, key)	{ key.mv_size = NODEKSZ(node); key.mv_data = NODEKEY(node); }

	/** Information about a single database in the environment. */
typedef struct MDB_db {
	uint32_t	md_xsize;	/**< also ksize for LEAF2 pages */
	uint16_t	md_flags;	/**< @ref mdb_dbi_open */
	uint16_t	md_depth;	/**< depth of this tree */
	pgno_t		md_branch_pages;	/**< number of internal pages */
	pgno_t		md_leaf_pages;		/**< number of leaf pages */
	pgno_t		md_overflow_pages;	/**< number of overflow pages */
	size_t		md_entries;		/**< number of data items */
	pgno_t		md_root;		/**< the root page of this tree */
} MDB_db;

	/** mdb_dbi_open flags */
#define MDB_VALID	0x8000		/**< DB handle is valid, for me_dbflags */
#define PERSISTENT_FLAGS	(0xffff & ~(MDB_VALID))
#define VALID_FLAGS	(MDB_REVERSEKEY|MDB_DUPSORT|MDB_INTEGERKEY|MDB_DUPFIXED|\
	MDB_INTEGERDUP|MDB_REVERSEDUP|MDB_CREATE)

	/** Handle for the DB used to track free pages. */
#define	FREE_DBI	0
	/** Handle for the default DB. */
#define	MAIN_DBI	1
	/** Number of DBs in metapage (free and main) - also hardcoded elsewhere */
#define CORE_DBS	2

	/** Number of meta pages - also hardcoded elsewhere */
#define NUM_METAS	2

	/** Meta page content.
	 *	A meta page is the start point for accessing a database snapshot.
	 *	Pages 0-1 are meta pages. Transaction N writes meta page #(N % 2).
	 */
typedef struct MDB_meta {
		/** Stamp identifying this as an LMDB file. It must be set
		 *	to #MDB_MAGIC. */
	uint32_t	mm_magic;
		/** Version number of this file. Must be set to #MDB_DATA_VERSION. */
	uint32_t	mm_version;
	void		*mm_address;		/**< address for fixed mapping */
	size_t		mm_mapsize;			/**< size of mmap region */
	MDB_db		mm_dbs[CORE_DBS];	/**< first is free space, 2nd is main db */
	/** The size of pages used in this DB */
#define	mm_psize	mm_dbs[FREE_DBI].md_xsize
	/** Any persistent environment flags. @ref mdb_env */
#define	mm_flags	mm_dbs[FREE_DBI].md_flags
	pgno_t		mm_last_pg;			/**< last used page in file */
	volatile txnid_t	mm_txnid;	/**< txnid that committed this page */
#define MDB_DATASIGN_NONE 0
#define MDB_DATASIGN_WEAK 1
	volatile uint64_t	mm_datasync_sign;
#define META_IS_WEAK(meta) ((meta)->mm_datasync_sign == MDB_DATASIGN_WEAK)
#define META_IS_STEADY(meta) ((meta)->mm_datasync_sign > MDB_DATASIGN_WEAK)
} MDB_meta;

	/** Buffer for a stack-allocated meta page.
	 *	The members define size and alignment, and silence type
	 *	aliasing warnings.  They are not used directly; that could
	 *	mean incorrectly using several union members in parallel.
	 */
typedef union MDB_metabuf {
	MDB_page	mb_page;
	struct {
		char		mm_pad[PAGEHDRSZ];
		MDB_meta	mm_meta;
	} mb_metabuf;
} MDB_metabuf;

	/** Auxiliary DB info.
	 *	The information here is mostly static/read-only. There is
	 *	only a single copy of this record in the environment.
	 */
typedef struct MDB_dbx {
	MDB_val		md_name;		/**< name of the database */
	MDB_cmp_func	*md_cmp;	/**< function for comparing keys */
	MDB_cmp_func	*md_dcmp;	/**< function for comparing data items */
	MDB_rel_func	*md_rel;	/**< user relocate function */
	void		*md_relctx;		/**< user-provided context for md_rel */
} MDB_dbx;

	/** A database transaction.
	 *	Every operation requires a transaction handle.
	 */
struct MDB_txn {
#define MDBX_MT_SIGNATURE 0x706C553B
	unsigned	mt_signature;
	MDB_txn		*mt_parent;		/**< parent of a nested txn */
	/** Nested txn under this txn, set together with flag #MDB_TXN_HAS_CHILD */
	MDB_txn		*mt_child;
	pgno_t		mt_next_pgno;	/**< next unallocated page */
	/** The ID of this transaction. IDs are integers incrementing from 1.
	 *	Only committed write transactions increment the ID. If a transaction
	 *	aborts, the ID may be re-used by the next writer.
	 */
	txnid_t		mt_txnid;
	MDB_env		*mt_env;		/**< the DB environment */
	/** The list of reclaimed txns from freeDB */
	MDB_IDL		mt_lifo_reclaimed;
	/** The list of pages that became unused during this transaction.
	 */
	MDB_IDL		mt_free_pgs;
	/** The list of loose pages that became unused and may be reused
	 *	in this transaction, linked through #NEXT_LOOSE_PAGE(page).
	 */
	MDB_page	*mt_loose_pgs;
	/* #Number of loose pages (#mt_loose_pgs) */
	int			mt_loose_count;
	/** The sorted list of dirty pages we temporarily wrote to disk
	 *	because the dirty list was full. page numbers in here are
	 *	shifted left by 1, deleted slots have the LSB set.
	 */
	MDB_IDL		mt_spill_pgs;
	union {
		/** For write txns: Modified pages. Sorted when not MDB_WRITEMAP. */
		MDB_ID2L	dirty_list;
		/** For read txns: This thread/txn's reader table slot, or NULL. */
		MDB_reader	*reader;
	} mt_u;
	/** Array of records for each DB known in the environment. */
	MDB_dbx		*mt_dbxs;
	/** Array of MDB_db records for each known DB */
	MDB_db		*mt_dbs;
	/** Array of sequence numbers for each DB handle */
	unsigned	*mt_dbiseqs;
/** @defgroup mt_dbflag	Transaction DB Flags
 *	@ingroup internal
 * @{
 */
#define DB_DIRTY	0x01		/**< DB was modified or is DUPSORT data */
#define DB_STALE	0x02		/**< Named-DB record is older than txnID */
#define DB_NEW		0x04		/**< Named-DB handle opened in this txn */
#define DB_VALID	0x08		/**< DB handle is valid, see also #MDB_VALID */
#define DB_USRVALID	0x10		/**< As #DB_VALID, but not set for #FREE_DBI */
/** @} */
	/** In write txns, array of cursors for each DB */
	MDB_cursor	**mt_cursors;
	/** Array of flags for each DB */
	unsigned char	*mt_dbflags;
	/**	Number of DB records in use, or 0 when the txn is finished.
	 *	This number only ever increments until the txn finishes; we
	 *	don't decrement it when individual DB handles are closed.
	 */
	MDB_dbi		mt_numdbs;

/** @defgroup mdb_txn	Transaction Flags
 *	@ingroup internal
 *	@{
 */
	/** #mdb_txn_begin() flags */
#define MDB_TXN_BEGIN_FLAGS	(MDB_NOMETASYNC|MDB_NOSYNC|MDB_RDONLY)
#define MDB_TXN_NOMETASYNC	MDB_NOMETASYNC	/**< don't sync meta for this txn on commit */
#define MDB_TXN_NOSYNC		MDB_NOSYNC	/**< don't sync this txn on commit */
#define MDB_TXN_RDONLY		MDB_RDONLY	/**< read-only transaction */
	/* internal txn flags */
#define MDB_TXN_WRITEMAP	MDB_WRITEMAP	/**< copy of #MDB_env flag in writers */
#define MDB_TXN_FINISHED	0x01		/**< txn is finished or never began */
#define MDB_TXN_ERROR		0x02		/**< txn is unusable after an error */
#define MDB_TXN_DIRTY		0x04		/**< must write, even if dirty list is empty */
#define MDB_TXN_SPILLS		0x08		/**< txn or a parent has spilled pages */
#define MDB_TXN_HAS_CHILD	0x10		/**< txn has an #MDB_txn.%mt_child */
	/** most operations on the txn are currently illegal */
#define MDB_TXN_BLOCKED		(MDB_TXN_FINISHED|MDB_TXN_ERROR|MDB_TXN_HAS_CHILD)
/** @} */
	unsigned	mt_flags;		/**< @ref mdb_txn */
	/** #dirty_list room: Array size - \#dirty pages visible to this txn.
	 *	Includes ancestor txns' dirty pages not hidden by other txns'
	 *	dirty/spilled pages. Thus commit(nested txn) has room to merge
	 *	dirty_list into mt_parent after freeing hidden mt_parent pages.
	 */
	unsigned	mt_dirty_room;
};

/** Enough space for 2^32 nodes with minimum of 2 keys per node. I.e., plenty.
 * At 4 keys per node, enough for 2^64 nodes, so there's probably no need to
 * raise this on a 64 bit machine.
 */
#define CURSOR_STACK		 32

struct MDB_xcursor;

	/** Cursors are used for all DB operations.
	 *	A cursor holds a path of (page pointer, key index) from the DB
	 *	root to a position in the DB, plus other state. #MDB_DUPSORT
	 *	cursors include an xcursor to the current data item. Write txns
	 *	track their cursors and keep them up to date when data moves.
	 *	Exception: An xcursor's pointer to a #P_SUBP page can be stale.
	 *	(A node with #F_DUPDATA but no #F_SUBDATA contains a subpage).
	 */
struct MDB_cursor {
#define MDBX_MC_SIGNATURE 0xFE05D5B1
	unsigned	mc_signature;
	/** Next cursor on this DB in this txn */
	MDB_cursor	*mc_next;
	/** Backup of the original cursor if this cursor is a shadow */
	MDB_cursor	*mc_backup;
	/** Context used for databases with #MDB_DUPSORT, otherwise NULL */
	struct MDB_xcursor	*mc_xcursor;
	/** The transaction that owns this cursor */
	MDB_txn		*mc_txn;
	/** The database handle this cursor operates on */
	MDB_dbi		mc_dbi;
	/** The database record for this cursor */
	MDB_db		*mc_db;
	/** The database auxiliary record for this cursor */
	MDB_dbx		*mc_dbx;
	/** The @ref mt_dbflag for this database */
	unsigned char	*mc_dbflag;
	unsigned short 	mc_snum;	/**< number of pushed pages */
	unsigned short	mc_top;		/**< index of top page, normally mc_snum-1 */
/** @defgroup mdb_cursor	Cursor Flags
 *	@ingroup internal
 *	Cursor state flags.
 *	@{
 */
#define C_INITIALIZED	0x01	/**< cursor has been initialized and is valid */
#define C_EOF	0x02			/**< No more data */
#define C_SUB	0x04			/**< Cursor is a sub-cursor */
#define C_DEL	0x08			/**< last op was a cursor_del */
#define C_UNTRACK	0x40		/**< Un-track cursor when closing */
#define C_RECLAIMING	0x80		/**< FreeDB lookup is prohibited */
/** @} */
	unsigned	mc_flags;	/**< @ref mdb_cursor */
	MDB_page	*mc_pg[CURSOR_STACK];	/**< stack of pushed pages */
	indx_t		mc_ki[CURSOR_STACK];	/**< stack of page indices */
};

	/** Context for sorted-dup records.
	 *	We could have gone to a fully recursive design, with arbitrarily
	 *	deep nesting of sub-databases. But for now we only handle these
	 *	levels - main DB, optional sub-DB, sorted-duplicate DB.
	 */
typedef struct MDB_xcursor {
	/** A sub-cursor for traversing the Dup DB */
	MDB_cursor mx_cursor;
	/** The database record for this Dup DB */
	MDB_db	mx_db;
	/**	The auxiliary DB record for this Dup DB */
	MDB_dbx	mx_dbx;
	/** The @ref mt_dbflag for this Dup DB */
	unsigned char mx_dbflag;
} MDB_xcursor;

	/** State of FreeDB old pages, stored in the MDB_env */
typedef struct MDB_pgstate {
	pgno_t		*mf_pghead;	/**< Reclaimed freeDB pages, or NULL before use */
	txnid_t		mf_pglast;	/**< ID of last used record, or 0 if !mf_pghead */
} MDB_pgstate;

	/** Context for deferred cleanup of reader's threads.
	*  to avoid https://github.com/ReOpen/ReOpenLDAP/issues/48 */
struct MDB_rthc {
	MDB_reader *rc_reader;
};
	/** The database environment. */
struct MDB_env {
#define MDBX_ME_SIGNATURE 0x9A899641
	unsigned	me_signature;
	HANDLE		me_fd;		/**< The main data file */
	HANDLE		me_lfd;		/**< The lock file */
	/** Failed to update the meta page. Probably an I/O error. */
#define	MDB_FATAL_ERROR	0x80000000U
	/** Some fields are initialized. */
#define	MDB_ENV_ACTIVE	0x20000000U
	/** me_txkey is set */
#define	MDB_ENV_TXKEY	0x10000000U
	uint32_t 	me_flags;		/**< @ref mdb_env */
	unsigned	me_psize;	/**< DB page size, inited from me_os_psize */
	unsigned	me_os_psize;	/**< OS page size, from #GET_PAGESIZE */
	unsigned	me_maxreaders;	/**< size of the reader table */
	/** Max #MDB_txninfo.%mti_numreaders of interest to #mdb_env_close() */
	unsigned	me_close_readers;
	MDB_dbi		me_numdbs;		/**< number of DBs opened */
	MDB_dbi		me_maxdbs;		/**< size of the DB table */
	pid_t	me_pid;		/**< process ID of this env */
	char		*me_path;		/**< path to the DB files */
	char		*me_map;		/**< the memory map of the data file */
	MDB_txninfo	*me_txns;		/**< the memory map of the lock file, never NULL */
	void		*me_pbuf;		/**< scratch area for DUPSORT put() */
	MDB_txn		*me_txn;		/**< current write transaction */
	MDB_txn		*me_txn0;		/**< prealloc'd write transaction */
	size_t		me_mapsize;		/**< size of the data memory map */
	pgno_t		me_maxpg;		/**< me_mapsize / me_psize */
	MDB_dbx		*me_dbxs;		/**< array of static DB info */
	uint16_t	*me_dbflags;	/**< array of flags from MDB_db.md_flags */
	unsigned	*me_dbiseqs;	/**< array of dbi sequence numbers */
	pthread_key_t	me_txkey;	/**< thread-key for readers */
	txnid_t		me_pgoldest;	/**< ID of oldest reader last time we looked */
	MDB_pgstate	me_pgstate;		/**< state of old pages from freeDB */
#	define		me_pglast	me_pgstate.mf_pglast
#	define		me_pghead	me_pgstate.mf_pghead
	MDB_page	*me_dpages;		/**< list of malloc'd blocks for re-use */
	/** IDL of pages that became unused in a write txn */
	MDB_IDL		me_free_pgs;
	/** ID2L of pages written during a write txn. Length MDB_IDL_UM_SIZE. */
	MDB_ID2L	me_dirty_list;
	/** Max number of freelist items that can fit in a single overflow page */
	unsigned	me_maxfree_1pg;
	/** Max size of a node on a page */
	unsigned	me_nodemax;
	unsigned	me_maxkey_limit;	/**< max size of a key */
	int		me_live_reader;		/**< have liveness lock in reader table */
	void		*me_userctx;	 /**< User-settable context */
#if MDB_DEBUG
	MDB_assert_func *me_assert_func; /**< Callback for assertion failures */
#endif
	uint64_t	me_sync_pending;	/**< Total dirty/commited bytes since the last mdb_env_sync() */
	uint64_t	me_sync_threshold;	/**< Treshold of above to force synchronous flush */
#if MDBX_MODE_ENABLED
	MDB_oom_func	*me_oom_func; /**< Callback for kicking laggard readers */
#endif
#ifdef USE_VALGRIND
	int me_valgrind_handle;
#endif
};

	/** Nested transaction */
typedef struct MDB_ntxn {
	MDB_txn		mnt_txn;		/**< the transaction */
	MDB_pgstate	mnt_pgstate;	/**< parent transaction's saved freestate */
} MDB_ntxn;

	/** max number of pages to commit in one writev() call */
#define MDB_COMMIT_PAGES	 64
#if defined(IOV_MAX) && IOV_MAX < MDB_COMMIT_PAGES
#	undef MDB_COMMIT_PAGES
#	define MDB_COMMIT_PAGES	IOV_MAX
#endif

	/** max bytes to write in one call */
#define MAX_WRITE		(0x80000000U >> (sizeof(ssize_t) == 4))

	/** Check \b txn and \b dbi arguments to a function */
#define TXN_DBI_EXIST(txn, dbi, validity) \
	((dbi)<(txn)->mt_numdbs && ((txn)->mt_dbflags[dbi] & (validity)))

	/** Check for misused \b dbi handles */
#define TXN_DBI_CHANGED(txn, dbi) \
	((txn)->mt_dbiseqs[dbi] != (txn)->mt_env->me_dbiseqs[dbi])

#define METAPAGE_1(env) \
	(&((MDB_metabuf*) (env)->me_map)->mb_metabuf.mm_meta)

#define METAPAGE_2(env) \
	(&((MDB_metabuf*) ((env)->me_map + env->me_psize))->mb_metabuf.mm_meta)

static int  mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp, int flags);
static int  mdb_page_new(MDB_cursor *mc, uint32_t flags, int num, MDB_page **mp);
static int  mdb_page_touch(MDB_cursor *mc);
static int  mdb_cursor_touch(MDB_cursor *mc);

#define MDB_END_NAMES {"committed", "empty-commit", "abort", "reset", \
	"reset-tmp", "fail-begin", "fail-beginchild"}
enum {
	/* mdb_txn_end operation number, for logging */
	MDB_END_COMMITTED, MDB_END_EMPTY_COMMIT, MDB_END_ABORT, MDB_END_RESET,
	MDB_END_RESET_TMP, MDB_END_FAIL_BEGIN, MDB_END_FAIL_BEGINCHILD
};
#define MDB_END_OPMASK	0x0F	/**< mask for #mdb_txn_end() operation number */
#define MDB_END_UPDATE	0x10	/**< update env state (DBIs) */
#define MDB_END_FREE	0x20	/**< free txn unless it is #MDB_env.%me_txn0 */
#define MDB_END_SLOT MDB_NOTLS	/**< release any reader slot if #MDB_NOTLS */
static int mdb_txn_end(MDB_txn *txn, unsigned mode);

static int  mdb_page_get(MDB_txn *txn, pgno_t pgno, MDB_page **mp, int *lvl);
static int  mdb_page_search_root(MDB_cursor *mc,
				MDB_val *key, int modify);
#define MDB_PS_MODIFY	1
#define MDB_PS_ROOTONLY	2
#define MDB_PS_FIRST	4
#define MDB_PS_LAST		8
static int  mdb_page_search(MDB_cursor *mc,
				MDB_val *key, int flags);
static int	mdb_page_merge(MDB_cursor *csrc, MDB_cursor *cdst);

#define MDB_SPLIT_REPLACE	MDB_APPENDDUP	/**< newkey is not new */
static int	mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata,
				pgno_t newpgno, unsigned nflags);

static int  mdb_env_read_header(MDB_env *env, MDB_meta *meta);
static int mdb_env_sync0(MDB_env *env, unsigned flags, MDB_meta *pending);
static void mdb_env_close0(MDB_env *env);

static MDB_node *mdb_node_search(MDB_cursor *mc, MDB_val *key, int *exactp);
static int  mdb_node_add(MDB_cursor *mc, indx_t indx,
				MDB_val *key, MDB_val *data, pgno_t pgno, unsigned flags);
static void mdb_node_del(MDB_cursor *mc, int ksize);
static void mdb_node_shrink(MDB_page *mp, indx_t indx);
static int	mdb_node_move(MDB_cursor *csrc, MDB_cursor *cdst, int fromleft);
static int  mdb_node_read(MDB_txn *txn, MDB_node *leaf, MDB_val *data);
static size_t	mdb_leaf_size(MDB_env *env, MDB_val *key, MDB_val *data);
static size_t	mdb_branch_size(MDB_env *env, MDB_val *key);

static int	mdb_rebalance(MDB_cursor *mc);
static int	mdb_update_key(MDB_cursor *mc, MDB_val *key);

static void	mdb_cursor_pop(MDB_cursor *mc);
static int	mdb_cursor_push(MDB_cursor *mc, MDB_page *mp);

static int	mdb_cursor_del0(MDB_cursor *mc);
static int	mdb_del0(MDB_txn *txn, MDB_dbi dbi, MDB_val *key, MDB_val *data, unsigned flags);
static int	mdb_cursor_sibling(MDB_cursor *mc, int move_right);
static int	mdb_cursor_next(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op);
static int	mdb_cursor_prev(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op);
static int	mdb_cursor_set(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op,
				int *exactp);
static int	mdb_cursor_first(MDB_cursor *mc, MDB_val *key, MDB_val *data);
static int	mdb_cursor_last(MDB_cursor *mc, MDB_val *key, MDB_val *data);

static void	mdb_cursor_init(MDB_cursor *mc, MDB_txn *txn, MDB_dbi dbi, MDB_xcursor *mx);
static void	mdb_xcursor_init0(MDB_cursor *mc);
static void	mdb_xcursor_init1(MDB_cursor *mc, MDB_node *node);
static void	mdb_xcursor_init2(MDB_cursor *mc, MDB_xcursor *src_mx, int force);

static int	mdb_drop0(MDB_cursor *mc, int subs);
static void mdb_default_cmp(MDB_txn *txn, MDB_dbi dbi);
static int mdb_reader_check0(MDB_env *env, int rlocked, int *dead);

/** @cond */
static MDB_cmp_func	mdb_cmp_memn, mdb_cmp_memnr, mdb_cmp_int_ai, mdb_cmp_int_a2, mdb_cmp_int_ua;
/** @endcond */

#ifdef __SANITIZE_THREAD__
static pthread_mutex_t tsan_mutex = PTHREAD_MUTEX_INITIALIZER;
#endif

/** Return the library version info. */
char * __cold
mdb_version(int *major, int *minor, int *patch)
{
	if (major) *major = MDB_VERSION_MAJOR;
	if (minor) *minor = MDB_VERSION_MINOR;
	if (patch) *patch = MDB_VERSION_PATCH;
	return MDB_VERSION_STRING;
}

/** Table of descriptions for LMDB @ref errors */
static char *const mdb_errstr[] = {
	"MDB_KEYEXIST: Key/data pair already exists",
	"MDB_NOTFOUND: No matching key/data pair found",
	"MDB_PAGE_NOTFOUND: Requested page not found",
	"MDB_CORRUPTED: Located page was wrong type",
	"MDB_PANIC: Update of meta page failed or environment had fatal error",
	"MDB_VERSION_MISMATCH: Database environment version mismatch",
	"MDB_INVALID: File is not an LMDB file",
	"MDB_MAP_FULL: Environment mapsize limit reached",
	"MDB_DBS_FULL: Environment maxdbs limit reached",
	"MDB_READERS_FULL: Environment maxreaders limit reached",
	"MDB_TLS_FULL: Thread-local storage keys full - too many environments open",
	"MDB_TXN_FULL: Transaction has too many dirty pages - transaction too big",
	"MDB_CURSOR_FULL: Internal error - cursor stack limit reached",
	"MDB_PAGE_FULL: Internal error - page has no more space",
	"MDB_MAP_RESIZED: Database contents grew beyond environment mapsize",
	"MDB_INCOMPATIBLE: Operation and DB incompatible, or DB flags changed",
	"MDB_BAD_RSLOT: Invalid reuse of reader locktable slot",
	"MDB_BAD_TXN: Transaction must abort, has a child, or is invalid",
	"MDB_BAD_VALSIZE: Unsupported size of key/DB name/data, or wrong DUPFIXED size",
	"MDB_BAD_DBI: The specified DBI handle was closed/changed unexpectedly",
};

char * __cold
mdb_strerror(int err)
{
	int i;
	if (!err)
		return ("Successful return: 0");

	if (err >= MDB_KEYEXIST && err <= MDB_LAST_ERRCODE) {
		i = err - MDB_KEYEXIST;
		return mdb_errstr[i];
	}

	return strerror(err);
}

#if MDBX_MODE_ENABLED

int mdb_runtime_flags = MDB_DBG_PRINT
#if MDB_DEBUG
		| MDB_DBG_ASSERT
#endif
#if MDB_DEBUG > 1
		| MDB_DBG_TRACE
#endif
#if MDB_DEBUG > 2
		| MDB_DBG_AUDIT
#endif
#if MDB_DEBUG > 3
		| MDB_DBG_EXTRA
#endif
	;

static MDB_debug_func *mdb_debug_logger;

#else /* MDBX_MODE_ENABLED */
#	define mdb_runtime_flags 0
#	define mdb_debug_logger ((void (*)(int, ...)) NULL)
#endif /* ! MDBX_MODE_ENABLED */

#if MDB_DEBUG
	static txnid_t mdb_debug_edge;

	static void mdb_debug_log(int type, const char *function, int line,
						  const char *fmt, ...);
	static void __cold
	mdb_assert_fail(MDB_env *env, const char *msg,
		const char *func, int line)
	{
		if (env && env->me_assert_func)
			env->me_assert_func(env, msg, func, line);
		else {
			if (mdb_debug_logger)
				mdb_debug_log(MDB_DBG_ASSERT, func, line, "assert: %s\n", msg);
			__assert_fail(msg, __FILE__, line, func);
		}
	}

#	define mdb_assert_enabled() \
		unlikely(mdb_runtime_flags & MDB_DBG_ASSERT)

#	define mdb_audit_enabled() \
		unlikely(mdb_runtime_flags & MDB_DBG_AUDIT)

#	define mdb_debug_enabled(type) \
		unlikely(mdb_runtime_flags & \
			(type & (MDB_DBG_TRACE | MDB_DBG_EXTRA)))

#else
#	define mdb_debug_enabled(type) (0)
#	define mdb_audit_enabled() (0)
#	define mdb_assert_enabled() (0)
#	define mdb_assert_fail(env, msg, func, line) \
		__assert_fail(msg, __FILE__, line, func)
#endif /* MDB_DEBUG */

#if MDBX_MODE_ENABLED
int __cold
mdbx_setup_debug(int flags, MDB_debug_func* logger, long edge_txn) {
	unsigned ret = mdb_runtime_flags;
	if (flags != (int) MDB_DBG_DNT)
		mdb_runtime_flags = flags;
	if (logger != (MDB_debug_func*) MDB_DBG_DNT)
		mdb_debug_logger = logger;
#if MDB_DEBUG
	if (edge_txn != (long) MDB_DBG_DNT)
		mdb_debug_edge = edge_txn;
#else
	(void) edge_txn;
#endif
	return ret;
}
#endif /* MDBX_MODE_ENABLED */

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

	va_start(args, fmt);
	if (mdb_debug_logger)
		mdb_debug_logger(type, function, line, fmt, args);
	else {
		if (function && line)
			fprintf(stderr, "%s:%u ", function, line);
		vfprintf(stderr, fmt, args);
	}
	va_end(args);
}

#define mdb_print(fmt, ...) \
	mdb_debug_log(MDB_DBG_PRINT, NULL, 0, fmt, ##__VA_ARGS__)

#define mdb_debug(fmt, ...) do { \
		if (mdb_debug_enabled(MDB_DBG_TRACE)) \
			mdb_debug_log(MDB_DBG_TRACE, __FUNCTION__, __LINE__, fmt "\n", ##__VA_ARGS__); \
	} while(0)

#define mdb_debug_print(fmt, ...) do { \
		if (mdb_debug_enabled(MDB_DBG_TRACE)) \
			mdb_debug_log(MDB_DBG_TRACE, NULL, 0, fmt, ##__VA_ARGS__); \
	} while(0)

#define mdb_debug_extra(fmt, ...) do { \
		if (mdb_debug_enabled(MDB_DBG_EXTRA)) \
			mdb_debug_log(MDB_DBG_EXTRA, __FUNCTION__, __LINE__, fmt, ##__VA_ARGS__); \
	} while(0)

#define mdb_debug_extra_print(fmt, ...) do { \
		if (mdb_debug_enabled(MDB_DBG_EXTRA)) \
			mdb_debug_log(MDB_DBG_EXTRA, NULL, 0, fmt, ##__VA_ARGS__); \
	} while(0)

#define mdb_ensure_msg(env, expr, msg) \
	do { \
		if (unlikely(!(expr))) \
			mdb_assert_fail(env, msg, __FUNCTION__, __LINE__); \
	} while(0)

#define mdb_ensure(env, expr) \
	mdb_ensure_msg(env, expr, #expr)

/** assert(3) variant in environment context */
#define mdb_assert(env, expr) \
	do { \
		if (mdb_assert_enabled()) \
			mdb_ensure(env, expr); \
	} while(0)

/** assert(3) variant in cursor context */
#define mdb_cassert(mc, expr) \
	mdb_assert((mc)->mc_txn->mt_env, expr)

/** assert(3) variant in transaction context */
#define mdb_tassert(txn, expr) \
	mdb_assert((txn)->mt_env, expr)

/** Return the page number of \b mp which may be sub-page, for debug output */
static MDB_INLINE pgno_t
mdb_dbg_pgno(MDB_page *mp)
{
	pgno_t ret;
	COPY_PGNO(ret, mp->mp_pgno);
	return ret;
}

/** Display a key in hexadecimal and return the address of the result.
 * @param[in] key the key to display
 * @param[in] buf the buffer to write into. Should always be #DKBUF.
 * @return The key in hexadecimal form.
 */
char *
mdb_dkey(MDB_val *key, char *buf)
{
	char *ptr = buf;
	unsigned char *c = key->mv_data;
	unsigned i;

	if (!key)
		return "";

	if (key->mv_size > DKBUF_MAXKEYSIZE)
		return "MDB_MAXKEYSIZE";
	/* may want to make this a dynamic check: if the key is mostly
	 * printable characters, print it as-is instead of converting to hex.
	 */
#if 1
	buf[0] = '\0';
	for (i=0; i<key->mv_size; i++)
		ptr += sprintf(ptr, "%02x", *c++);
#else
	sprintf(buf, "%.*s", key->mv_size, key->mv_data);
#endif
	return buf;
}

#if 0 /* LY: debug stuff */
static const char *
mdb_leafnode_type(MDB_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
mdb_page_list(MDB_page *mp)
{
	pgno_t pgno = mdb_dbg_pgno(mp);
	const char *type, *state = (mp->mp_flags & P_DIRTY) ? ", dirty" : "";
	MDB_node *node;
	unsigned i, nkeys, nsize, total = 0;
	MDB_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:
		mdb_print("Overflow page %zu pages %u%s\n",
			pgno, mp->mp_pages, state);
		return;
	case P_META:
		mdb_print("Meta-page %zu txnid %zu\n",
			pgno, ((MDB_meta *)PAGEDATA(mp))->mm_txnid);
		return;
	default:
		mdb_print("Bad page %zu flags 0x%u\n", pgno, mp->mp_flags);
		return;
	}

	nkeys = NUMKEYS(mp);
	mdb_print("%s %zu numkeys %d%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.mv_size = nsize = mp->mp_ksize;
			key.mv_data = LEAF2KEY(mp, i, nsize);
			total += nsize;
			mdb_print("key %d: nsize %d, %s\n", i, nsize, DKEY(&key));
			continue;
		}
		node = NODEPTR(mp, i);
		key.mv_size = node->mn_ksize;
		key.mv_data = node->mn_data;
		nsize = NODESIZE + key.mv_size;
		if (IS_BRANCH(mp)) {
			mdb_print("key %d: page %zu, %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);
			mdb_print("key %d: nsize %d, %s%s\n",
				i, nsize, DKEY(&key), mdb_leafnode_type(node));
		}
		total = EVEN(total);
	}
	mdb_print("Total: header %d + contents %d + unused %d\n",
		IS_LEAF2(mp) ? PAGEHDRSZ : PAGEBASE + mp->mp_lower, total, SIZELEFT(mp));
}

static void
mdb_cursor_chk(MDB_cursor *mc)
{
	unsigned i;
	MDB_node *node;
	MDB_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))
			mdb_print("oops!\n");
	}
	if (unlikely(mc->mc_ki[i] >= NUMKEYS(mc->mc_pg[i])))
		mdb_print("ack!\n");
	if (mc->mc_xcursor && (mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED)) {
		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)) {
			mdb_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 mdb_audit(MDB_txn *txn)
{
	MDB_cursor mc;
	MDB_val key, data;
	MDB_ID freecount, count;
	MDB_dbi i;
	int rc;

	freecount = 0;
	mdb_cursor_init(&mc, txn, FREE_DBI, NULL);
	while ((rc = mdb_cursor_get(&mc, &key, &data, MDB_NEXT)) == 0)
		freecount += *(MDB_ID *)data.mv_data;
	mdb_tassert(txn, rc == MDB_NOTFOUND);

	count = 0;
	for (i = 0; i<txn->mt_numdbs; i++) {
		MDB_xcursor mx;
		if (!(txn->mt_dbflags[i] & DB_VALID))
			continue;
		mdb_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 & MDB_DUPSORT) {
			rc = mdb_page_search(&mc, NULL, MDB_PS_FIRST);
			for (; rc == MDB_SUCCESS; rc = mdb_cursor_sibling(&mc, 1)) {
				unsigned j;
				MDB_page *mp;
				mp = mc.mc_pg[mc.mc_top];
				for (j=0; j<NUMKEYS(mp); j++) {
					MDB_node *leaf = NODEPTR(mp, j);
					if (leaf->mn_flags & F_SUBDATA) {
						MDB_db db;
						memcpy(&db, NODEDATA(leaf), sizeof(db));
						count += db.md_branch_pages + db.md_leaf_pages +
							db.md_overflow_pages;
					}
				}
			}
			mdb_tassert(txn, rc == MDB_NOTFOUND);
		}
	}
	if (freecount + count + NUM_METAS != txn->mt_next_pgno) {
		mdb_print("audit: %lu freecount: %lu count: %lu total: %lu next_pgno: %lu\n",
			txn->mt_txnid, freecount, count+NUM_METAS,
			freecount+count+NUM_METAS, txn->mt_next_pgno);
	}
}

int
mdb_cmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b)
{
	mdb_ensure(NULL, txn->mt_signature == MDBX_MT_SIGNATURE);
	return txn->mt_dbxs[dbi].md_cmp(a, b);
}

int
mdb_dcmp(MDB_txn *txn, MDB_dbi dbi, const MDB_val *a, const MDB_val *b)
{
	mdb_ensure(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.
 */
static MDB_page *
mdb_page_malloc(MDB_txn *txn, unsigned num)
{
	MDB_env *env = txn->mt_env;
	size_t size = env->me_psize;
	MDB_page *np = env->me_dpages;
	if (likely(num == 1 && np)) {
		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 *= num;
		np = malloc(size);
		if (unlikely(! np)) {
			txn->mt_flags |= MDB_TXN_ERROR;
			return np;
		}
		VALGRIND_MEMPOOL_ALLOC(env, np, size);
	}

	if ((env->me_flags & MDB_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 += (num - 1) * env->me_psize;
		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 MDB_INLINE void
mdb_page_free(MDB_env *env, MDB_page *mp)
{
	mp->mp_next = env->me_dpages;
	VALGRIND_MEMPOOL_FREE(env, mp);
	env->me_dpages = mp;
}

/** Free a dirty page */
static void
mdb_dpage_free(MDB_env *env, MDB_page *dp)
{
	if (!IS_OVERFLOW(dp) || dp->mp_pages == 1) {
		mdb_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
mdb_dlist_free(MDB_txn *txn)
{
	MDB_env *env = txn->mt_env;
	MDB_ID2L dl = txn->mt_u.dirty_list;
	unsigned i, n = dl[0].mid;

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

static void __cold
mdb_kill_page(MDB_env *env, pgno_t pgno)
{
	const size_t offs = env->me_psize * pgno;
	const size_t shift = offsetof(MDB_page, mp_pb);

	if (env->me_flags & MDB_WRITEMAP) {
		MDB_page *mp = (MDB_page *)(env->me_map + offs);
		memset(&mp->mp_pb, 0x6F /* 'o', 111 */, env->me_psize - shift);
		VALGRIND_MAKE_MEM_NOACCESS(&mp->mp_pb, env->me_psize - shift);
	} else {
		struct iovec iov[1];
		iov[0].iov_len = env->me_psize - shift;
		iov[0].iov_base = alloca(iov[0].iov_len);
		memset(iov[0].iov_base, 0x6F /* 'o', 111 */, iov[0].iov_len);
		ssize_t rc = pwritev(env->me_fd, iov, 1, offs + shift);
		assert(rc == (ssize_t) iov[0].iov_len);
		(void) rc;
	}
}

/** 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
mdb_page_loose(MDB_cursor *mc, MDB_page *mp)
{
	int loose = 0;
	pgno_t pgno = mp->mp_pgno;
	MDB_txn *txn = mc->mc_txn;

	if ((mp->mp_flags & P_DIRTY) && mc->mc_dbi != FREE_DBI) {
		if (txn->mt_parent) {
			MDB_ID2 *dl = txn->mt_u.dirty_list;
			/* If txn has a parent, make sure the page is in our
			 * dirty list.
			 */
			if (dl[0].mid) {
				unsigned x = mdb_mid2l_search(dl, pgno);
				if (x <= dl[0].mid && dl[x].mid == pgno) {
					if (unlikely(mp != dl[x].mptr)) { /* bad cursor? */
						mc->mc_flags &= ~(C_INITIALIZED|C_EOF);
						txn->mt_flags |= MDB_TXN_ERROR;
						return MDB_CORRUPTED;
					}
					/* ok, it's ours */
					loose = 1;
				}
			}
		} else {
			/* no parent txn, so it's just ours */
			loose = 1;
		}
	}
	if (loose) {
		mdb_debug("loosen db %d page %zu", DDBI(mc), mp->mp_pgno);
		if (unlikely(txn->mt_env->me_flags & MDB_PAGEPERTURB))
			mdb_kill_page(txn->mt_env, pgno);
		NEXT_LOOSE_PAGE(mp) = txn->mt_loose_pgs;
		txn->mt_loose_pgs = mp;
		txn->mt_loose_count++;
		mp->mp_flags |= P_LOOSE;
	} else {
		int rc = mdb_midl_append(&txn->mt_free_pgs, pgno);
		if (unlikely(rc))
			return rc;
	}

	return MDB_SUCCESS;
}

/** Set or clear P_KEEP in dirty, non-overflow, non-sub pages watched by txn.
 * @param[in] mc A cursor handle for the current operation.
 * @param[in] pflags Flags of the pages to update:
 * P_DIRTY to set P_KEEP, P_DIRTY|P_KEEP to clear it.
 * @param[in] all No shortcuts. Needed except after a full #mdb_page_flush().
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_pages_xkeep(MDB_cursor *mc, unsigned pflags, int all)
{
	enum { Mask = P_SUBP|P_DIRTY|P_LOOSE|P_KEEP };
	MDB_txn *txn = mc->mc_txn;
	MDB_cursor *m3;
	MDB_xcursor *mx;
	MDB_page *dp, *mp;
	MDB_node *leaf;
	unsigned i, j;
	int rc = MDB_SUCCESS, level;

	/* Mark pages seen by cursors */
	if (mc->mc_flags & C_UNTRACK)
		mc = NULL;				/* will find mc in mt_cursors */
	for (i = txn->mt_numdbs;; mc = txn->mt_cursors[--i]) {
		for (; mc; mc=mc->mc_next) {
			if (!(mc->mc_flags & C_INITIALIZED))
				continue;
			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;
			}
		}
		if (i == 0)
			break;
	}

	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 ((rc = mdb_page_get(txn, pgno, &dp, &level)) != MDB_SUCCESS)
					break;
				if ((dp->mp_flags & Mask) == pflags && level <= 1)
					dp->mp_flags ^= P_KEEP;
			}
		}
	}

	return rc;
}

static int mdb_page_flush(MDB_txn *txn, int keep);

/**	Spill pages from the dirty list back to disk.
 * This is intended to prevent running into #MDB_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 #MDB_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 #mdb_txn_begin() of a child txn, if
 *	 the parent's dirty_room is below a given threshold.
 *
 * Otherwise, if not using nested txns, it is expected that apps will
 * not run into #MDB_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 #mdb_page_touch(). Such references are
 * handled by #mdb_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.
 *
 * @param[in] m0 cursor A cursor handle identifying the transaction and
 *	database for which we are checking space.
 * @param[in] key For a put operation, the key being stored.
 * @param[in] data For a put operation, the data being stored.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_spill(MDB_cursor *m0, MDB_val *key, MDB_val *data)
{
	MDB_txn *txn = m0->mc_txn;
	MDB_page *dp;
	MDB_ID2L dl = txn->mt_u.dirty_list;
	unsigned i, j, need;
	int rc;

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

	/* Estimate how much space this op will take */
	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 += (LEAFSIZE(key, data) + txn->mt_env->me_psize) / txn->mt_env->me_psize;
	i += i;	/* double it for good measure */
	need = i;

	if (txn->mt_dirty_room > i)
		return MDB_SUCCESS;

	if (!txn->mt_spill_pgs) {
		txn->mt_spill_pgs = mdb_midl_alloc(MDB_IDL_UM_MAX);
		if (unlikely(!txn->mt_spill_pgs))
			return ENOMEM;
	} else {
		/* purge deleted slots */
		MDB_IDL sl = txn->mt_spill_pgs;
		unsigned 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 */
	rc = mdb_pages_xkeep(m0, P_DIRTY, 1);
	if (unlikely(rc != MDB_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 < MDB_IDL_UM_MAX / 8)
		need = MDB_IDL_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--) {
		MDB_ID pn = dl[i].mid << 1;
		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) {
			MDB_txn *tx2;
			for (tx2 = txn->mt_parent; tx2; tx2 = tx2->mt_parent) {
				if (tx2->mt_spill_pgs) {
					j = mdb_midl_search(tx2->mt_spill_pgs, pn);
					if (j <= tx2->mt_spill_pgs[0] && tx2->mt_spill_pgs[j] == pn) {
						dp->mp_flags |= P_KEEP;
						break;
					}
				}
			}
			if (tx2)
				continue;
		}
		rc = mdb_midl_append(&txn->mt_spill_pgs, pn);
		if (unlikely(rc != MDB_SUCCESS))
			goto bailout;
		need--;
	}
	mdb_midl_sort(txn->mt_spill_pgs);

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

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

bailout:
	txn->mt_flags |= rc ? MDB_TXN_ERROR : MDB_TXN_SPILLS;
	return rc;
}

static MDB_INLINE uint64_t
mdb_meta_sign(MDB_meta *meta) {
	uint64_t sign = MDB_DATASIGN_NONE;
#if 0 /* TODO */
	sign = hippeus_hash64(
				&meta->mm_mapsize,
				sizeof(MDB_meta) - offsetof(MDB_meta, mm_mapsize),
				meta->mm_version | (uint64_t) MDB_MAGIC << 32
			);
#else
	(void) meta;
#endif
	/* LY: newer returns MDB_DATASIGN_NONE or MDB_DATASIGN_WEAK */
	return (sign > MDB_DATASIGN_WEAK) ? sign : ~sign;
}

static MDB_INLINE MDB_meta*
mdb_meta_head_w(MDB_env *env) {
	MDB_meta* a = METAPAGE_1(env);
	MDB_meta* b = METAPAGE_2(env);
	txnid_t head_txnid = env->me_txns->mti_txnid;

	mdb_assert(env, a->mm_txnid != b->mm_txnid || head_txnid == 0);
	if (a->mm_txnid == head_txnid)
		return a;
	if (likely(b->mm_txnid == head_txnid))
		return b;

	mdb_debug("me_txns->mti_txnid not match meta-pages");
	mdb_assert(env, head_txnid == a->mm_txnid || head_txnid == b->mm_txnid);
	env->me_flags |= MDB_FATAL_ERROR;
	return a;
}

static MDB_meta*
mdb_meta_head_r(MDB_env *env) {
	MDB_meta* a = METAPAGE_1(env);
	MDB_meta* b = METAPAGE_2(env), *h;

#ifdef __SANITIZE_THREAD__
	pthread_mutex_lock(&tsan_mutex);
#endif

	txnid_t head_txnid = env->me_txns->mti_txnid;
	mdb_assert(env, a->mm_txnid != b->mm_txnid || head_txnid == 0);
	if (likely(a->mm_txnid == head_txnid)) {
		h = a;
	} else if (likely(b->mm_txnid == head_txnid)) {
		h = b;
	} else {
		/* LY: seems got a collision with mdb_env_sync0() */
		mdb_coherent_barrier();
		head_txnid = env->me_txns->mti_txnid;
		mdb_assert(env, a->mm_txnid != b->mm_txnid || head_txnid == 0);

		if (likely(a->mm_txnid == head_txnid)) {
			h = a;
		} else if (likely(b->mm_txnid == head_txnid)) {
			h = b;
		} else {
			/* LY: got a race again, or DB is corrupted */
			int rc = mdb_mutex_lock(env, MDB_MUTEX(env, w));
			h = mdb_meta_head_w(env);
			if (rc == 0)
				mdb_mutex_unlock(env, MDB_MUTEX(env, w));
		}
	}

#ifdef __SANITIZE_THREAD__
	pthread_mutex_unlock(&tsan_mutex);
#endif

	return h;
}

static MDB_INLINE MDB_meta*
mdb_env_meta_flipflop(const MDB_env *env, MDB_meta* meta) {
	return (meta == METAPAGE_1(env)) ? METAPAGE_2(env) : METAPAGE_1(env);
}

static MDB_INLINE int
mdb_meta_lt(MDB_meta* a, MDB_meta* b) {
	return (META_IS_STEADY(a) == META_IS_STEADY(b))
			? a->mm_txnid < b->mm_txnid : META_IS_STEADY(b);
}

/** Find oldest txnid still referenced. */
static
txnid_t mdb_find_oldest(MDB_env *env, int *laggard)
{
#ifdef __SANITIZE_THREAD__
	pthread_mutex_lock(&tsan_mutex);
#endif
	int i, reader;
	MDB_reader *r = env->me_txns->mti_readers;
	txnid_t oldest = env->me_txns->mti_txnid;

	MDB_meta* a = METAPAGE_1(env);
	MDB_meta* b = METAPAGE_2(env);
	if (META_IS_WEAK(a) && oldest > b->mm_txnid)
		oldest = b->mm_txnid;
	if (META_IS_WEAK(b) && oldest > a->mm_txnid)
		oldest = a->mm_txnid;

	for (reader = -1, i = env->me_txns->mti_numreaders; --i >= 0; ) {
		if (r[i].mr_pid) {
			txnid_t snap = r[i].mr_txnid;
			if (oldest > snap) {
				oldest = snap;
				reader = i;
			}
		}
	}
#ifdef __SANITIZE_THREAD__
	pthread_mutex_unlock(&tsan_mutex);
#endif

	if (laggard)
		*laggard = reader;
	return oldest;
}

static int __cold
mdb_oomkick(MDB_env *env, txnid_t oldest)
{
	int retry;
	txnid_t snap;

	for(retry = 0; ; ++retry) {
		int reader;

		if (mdb_reader_check(env, NULL))
			break;

		snap = mdb_find_oldest(env, &reader);
		if (oldest < snap)
			return 1;

		if (reader < 0)
			return 0;

#if MDBX_MODE_ENABLED
		{
			MDB_reader *r;
			pthread_t tid;
			pid_t pid;
			int rc;

			if (!env->me_oom_func)
				break;

			r = &env->me_txns->mti_readers[ reader ];
			pid = r->mr_pid;
			tid = r->mr_tid;
			if (r->mr_txnid != oldest || pid <= 0)
				continue;

			rc = env->me_oom_func(env, pid, (void*) tid, oldest,
				mdb_meta_head_w(env)->mm_txnid - oldest, retry);
			if (rc < 0)
				break;

			if (rc) {
				r->mr_txnid = ~(txnid_t)0;
				if (rc > 1) {
					r->mr_tid = 0;
					r->mr_pid = 0;
					mdb_coherent_barrier();
				}
			}
		}
#else
		break;
#endif /* MDBX_MODE_ENABLED */
	}

	snap = mdb_find_oldest(env, NULL);
	return oldest < snap;
}

/** Add a page to the txn's dirty list */
static void
mdb_page_dirty(MDB_txn *txn, MDB_page *mp)
{
	MDB_ID2 mid;
	int rc, (*insert)(MDB_ID2L, MDB_ID2 *);

	if (txn->mt_flags & MDB_TXN_WRITEMAP) {
		insert = mdb_mid2l_append;
	} else {
		insert = mdb_mid2l_insert;
	}
	mid.mid = mp->mp_pgno;
	mid.mptr = mp;
	rc = insert(txn->mt_u.dirty_list, &mid);
	mdb_tassert(txn, rc == 0);
	txn->mt_dirty_room--;
}

/** Allocate page numbers and memory for writing.  Maintain me_pglast,
 * me_pghead and mt_next_pgno.
 *
 * 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_pghead[]
 * and move me_pglast to say which records were consumed.  Only this
 * function can create me_pghead and move me_pglast/mt_next_pgno.
 * @param[in] mc cursor A cursor handle identifying the transaction and
 *	database for which we are allocating.
 * @param[in] num the number of pages to allocate.
 * @param[out] mp Address of the allocated page(s). Requests for multiple pages
 *  will always be satisfied by a single contiguous chunk of memory.
 * @return 0 on success, non-zero on failure.
 */

#define MDB_ALLOC_CACHE	1
#define MDB_ALLOC_GC	2
#define MDB_ALLOC_NEW	4
#define MDB_ALLOC_ALL	(MDB_ALLOC_CACHE|MDB_ALLOC_GC|MDB_ALLOC_NEW)

static int
mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp, int flags)
{
	int rc;
	MDB_txn *txn = mc->mc_txn;
	MDB_env *env = txn->mt_env;
	pgno_t pgno, *mop = env->me_pghead;
	unsigned i = 0, j, mop_len = mop ? mop[0] : 0, n2 = num-1;
	MDB_page *np;
	txnid_t oldest = 0, last = 0;
	MDB_cursor_op op;
	MDB_cursor m2;
	int found_old;

	if (likely(flags & MDB_ALLOC_GC)) {
		flags |= env->me_flags & (MDB_COALESCE | MDB_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 &= ~(MDB_ALLOC_GC | MDB_COALESCE | MDB_LIFORECLAIM);
		}
	}

	if (likely(flags & MDB_ALLOC_CACHE)) {
		/* If there are any loose pages, just use them */
		assert(mp && num);
		if (likely(num == 1 && txn->mt_loose_pgs)) {
			np = txn->mt_loose_pgs;
			txn->mt_loose_pgs = NEXT_LOOSE_PAGE(np);
			txn->mt_loose_count--;
			mdb_debug("db %d use loose page %zu", DDBI(mc), np->mp_pgno);
			*mp = np;
			return MDB_SUCCESS;
		}
	}

	/* If our dirty list is already full, we can't do anything */
	if (unlikely(txn->mt_dirty_room == 0)) {
		rc = MDB_TXN_FULL;
		goto fail;
	}

	for (;;) { /* oom-kick retry loop */
		found_old = 0;
		for (op = MDB_FIRST;; op = (flags & MDB_LIFORECLAIM) ? MDB_PREV : MDB_NEXT) {
			MDB_val key, data;
			MDB_node *leaf;
			pgno_t *idl;

			/* Seek a big enough contiguous page range. Prefer
			 * pages at the tail, just truncating the list.
			 */
			if (likely(flags & MDB_ALLOC_CACHE)
					&& mop_len > n2
					&& ( !(flags & MDB_COALESCE) || op == MDB_FIRST)) {
				i = mop_len;
				do {
					pgno = mop[i];
					if (likely(mop[i-n2] == pgno+n2))
						goto done;
				} while (--i > n2);
			}

			if (op == MDB_FIRST) {	/* 1st iteration */
				/* Prepare to fetch more and coalesce */
				if (unlikely( !(flags & MDB_ALLOC_GC) ))
					break;

				oldest = env->me_pgoldest;
				mdb_cursor_init(&m2, txn, FREE_DBI, NULL);
				if (flags & MDB_LIFORECLAIM) {
					if (env->me_pglast > 1) {
						/* Continue lookup from env->me_pglast to lower/first */
						last = env->me_pglast - 1;
						op = MDB_SET_RANGE;
					} else {
						oldest = mdb_find_oldest(env, NULL);
						env->me_pgoldest = oldest;
						found_old = 1;
						/* Begin from oldest reader if any */
						if (oldest > 2) {
							last = oldest - 1;
							op = MDB_SET_RANGE;
						}
					}
				} else if (env->me_pglast) {
					/* Continue lookup from env->me_pglast to higher/last */
					last = env->me_pglast;
					op = MDB_SET_RANGE;
				}

				key.mv_data = &last;
				key.mv_size = sizeof(last);
			}

			if (! (flags & MDB_LIFORECLAIM) ) {
				/* Do not fetch more if the record will be too recent */
				if (op != MDB_FIRST && ++last >= oldest) {
					if (!found_old) {
						oldest = mdb_find_oldest(env, NULL);
						env->me_pgoldest = oldest;
						found_old = 1;
					}
					if (oldest <= last)
						break;
				}
			}

			rc = mdb_cursor_get(&m2, &key, NULL, op);
			if (rc == MDB_NOTFOUND && (flags & MDB_LIFORECLAIM)) {
				if (op == MDB_SET_RANGE)
					continue;
				env->me_pgoldest = mdb_find_oldest(env, NULL);
				found_old = 1;
				if (oldest < env->me_pgoldest) {
					oldest = env->me_pgoldest;
					last = oldest - 1;
					key.mv_data = &last;
					key.mv_size = sizeof(last);
					op = MDB_SET_RANGE;
					rc = mdb_cursor_get(&m2, &key, NULL, op);
				}
			}
			if (unlikely(rc)) {
				if (rc == MDB_NOTFOUND)
					break;
				goto fail;
			}

			last = *(txnid_t*)key.mv_data;
			if (oldest <= last) {
				if (!found_old) {
					oldest = mdb_find_oldest(env, NULL);
					env->me_pgoldest = oldest;
					found_old = 1;
				}
				if (oldest <= last) {
					if (flags & MDB_LIFORECLAIM)
						continue;
					break;
				}
			}

			if (flags & MDB_LIFORECLAIM) {
				if (txn->mt_lifo_reclaimed) {
					for(j = txn->mt_lifo_reclaimed[0]; j > 0; --j)
						if (txn->mt_lifo_reclaimed[j] == last)
							break;
					if (j)
						continue;
				}
			}

			np = m2.mc_pg[m2.mc_top];
			leaf = NODEPTR(np, m2.mc_ki[m2.mc_top]);
			if (unlikely((rc = mdb_node_read(txn, leaf, &data)) != MDB_SUCCESS))
				goto fail;

			if ((flags & MDB_LIFORECLAIM) && !txn->mt_lifo_reclaimed) {
				txn->mt_lifo_reclaimed = mdb_midl_alloc(env->me_maxfree_1pg);
				if (unlikely(!txn->mt_lifo_reclaimed)) {
					rc = ENOMEM;
					goto fail;
				}
			}

			idl = (MDB_ID *) data.mv_data;
			mdb_tassert(txn, idl[0] == 0 || data.mv_size == (idl[0] + 1) * sizeof(MDB_ID));
			i = idl[0];
			if (!mop) {
				if (unlikely(!(env->me_pghead = mop = mdb_midl_alloc(i)))) {
					rc = ENOMEM;
					goto fail;
				}
			} else {
				if (unlikely((rc = mdb_midl_need(&env->me_pghead, i)) != 0))
					goto fail;
				mop = env->me_pghead;
			}
			if (flags & MDB_LIFORECLAIM) {
				if ((rc = mdb_midl_append(&txn->mt_lifo_reclaimed, last)) != 0)
					goto fail;
			}
			env->me_pglast = last;

			if (mdb_debug_enabled(MDB_DBG_EXTRA)) {
				mdb_debug_extra("IDL read txn %zu root %zu num %u, IDL",
					last, txn->mt_dbs[FREE_DBI].md_root, i);
				for (j = i; j; j--)
					mdb_debug_extra_print(" %zu", idl[j]);
				mdb_debug_extra_print("\n");
			}

			/* Merge in descending sorted order */
			mdb_midl_xmerge(mop, idl);
			mop_len = mop[0];

			if (unlikely((flags & MDB_ALLOC_CACHE) == 0)) {
				/* force gc reclaim mode */
				return MDB_SUCCESS;
			}

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

		if ((flags & (MDB_COALESCE|MDB_ALLOC_CACHE)) == (MDB_COALESCE|MDB_ALLOC_CACHE)
				&& mop_len > n2) {
			i = mop_len;
			do {
				pgno = mop[i];
				if (mop[i-n2] == pgno+n2)
					goto done;
			} while (--i > n2);
		}

		i = 0;
		rc = MDB_NOTFOUND;
		if (likely(flags & MDB_ALLOC_NEW)) {
			/* Use new pages from the map when nothing suitable in the freeDB */
			pgno = txn->mt_next_pgno;
			if (likely(pgno + num <= env->me_maxpg))
				goto done;
			mdb_debug("DB size maxed out");
			rc = MDB_MAP_FULL;
		}

		if (flags & MDB_ALLOC_GC) {
			MDB_meta* head = mdb_meta_head_w(env);
			MDB_meta* tail = mdb_env_meta_flipflop(env, head);

			if (oldest == tail->mm_txnid
					&& META_IS_WEAK(head) && !META_IS_WEAK(tail)) {
				MDB_meta meta = *head;
				/* 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
				 * MDB_NOSYNC and MDB_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. */

				mdb_debug("kick-gc: head %zu/%c, tail %zu/%c, oldest %zu, txnid %zu",
					head->mm_txnid, META_IS_WEAK(head) ? 'W' : 'N',
					tail->mm_txnid, META_IS_WEAK(tail) ? 'W' : 'N',
					oldest, env->me_txns->mt1.mtb.mtb_txnid );

				int flags = env->me_flags & MDB_WRITEMAP;
				if ((env->me_flags & MDB_UTTERLY_NOSYNC) == MDB_UTTERLY_NOSYNC)
					flags |= MDB_UTTERLY_NOSYNC;

				mdb_assert(env, env->me_sync_pending > 0);
				if (mdb_env_sync0(env, flags, &meta) == MDB_SUCCESS) {
					txnid_t snap = mdb_find_oldest(env, NULL);
					if (snap > oldest)
						continue;
				}
			}

			if (rc == MDB_MAP_FULL && mdb_oomkick(env, oldest))
				continue;
		}

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

done:
	assert(mp && num);
	if (env->me_flags & MDB_WRITEMAP) {
		np = (MDB_page *)(env->me_map + env->me_psize * pgno);
		/* LY: reset no-access flag from mdb_kill_page() */
		VALGRIND_MAKE_MEM_UNDEFINED(np, env->me_psize * num);
	} else {
		if (unlikely(!(np = mdb_page_malloc(txn, num)))) {
			rc = ENOMEM;
			goto fail;
		}
	}
	if (i) {
		mop[0] = mop_len -= num;
		/* Move any stragglers down */
		for (j = i-num; j < mop_len; )
			mop[++j] = mop[++i];
	} else {
		txn->mt_next_pgno = pgno + num;
	}

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

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

	return MDB_SUCCESS;
}

/** Copy the used portions of a non-overflow page.
 * @param[in] dst page to copy into
 * @param[in] src page to copy from
 * @param[in] psize size of a page
 */
static void
mdb_page_copy(MDB_page *dst, MDB_page *src, unsigned psize)
{
	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 + PAGEBASE) & -Align;
		memcpy(dst, src, (lower + PAGEBASE + (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.
 * @param[in] txn the transaction handle.
 * @param[in] mp the page being referenced. It must not be dirty.
 * @param[out] ret the writable page, if any. ret is unchanged if
 * mp wasn't spilled.
 */
static int
mdb_page_unspill(MDB_txn *txn, MDB_page *mp, MDB_page **ret)
{
	MDB_env *env = txn->mt_env;
	const MDB_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_pgs)
			continue;
		x = mdb_midl_search(tx2->mt_spill_pgs, pn);
		if (x <= tx2->mt_spill_pgs[0] && tx2->mt_spill_pgs[x] == pn) {
			MDB_page *np;
			int num;
			if (txn->mt_dirty_room == 0)
				return MDB_TXN_FULL;
			if (IS_OVERFLOW(mp))
				num = mp->mp_pages;
			else
				num = 1;
			if (env->me_flags & MDB_WRITEMAP) {
				np = mp;
			} else {
				np = mdb_page_malloc(txn, num);
				if (unlikely(!np))
					return ENOMEM;
				if (num > 1)
					memcpy(np, mp, num * env->me_psize);
				else
					mdb_page_copy(np, mp, env->me_psize);
			}
			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_pgs[0])
					txn->mt_spill_pgs[0]--;
				else
					txn->mt_spill_pgs[x] |= 1;
			}	/* otherwise, if belonging to a parent txn, the
				 * page remains spilled until child commits
				 */

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

/** Touch a page: make it dirty and re-insert into tree with updated pgno.
 * @param[in] mc cursor pointing to the page to be touched
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_touch(MDB_cursor *mc)
{
	MDB_page *mp = mc->mc_pg[mc->mc_top], *np;
	MDB_txn *txn = mc->mc_txn;
	MDB_cursor *m2, *m3;
	pgno_t	pgno;
	int rc;

	if (!F_ISSET(mp->mp_flags, P_DIRTY)) {
		if (txn->mt_flags & MDB_TXN_SPILLS) {
			np = NULL;
			rc = mdb_page_unspill(txn, mp, &np);
			if (unlikely(rc))
				goto fail;
			if (likely(np))
				goto done;
		}
		if (unlikely((rc = mdb_midl_need(&txn->mt_free_pgs, 1)) ||
			(rc = mdb_page_alloc(mc, 1, &np, MDB_ALLOC_ALL))))
			goto fail;
		pgno = np->mp_pgno;
		mdb_debug("touched db %d page %zu -> %zu", DDBI(mc), mp->mp_pgno, pgno);
		mdb_cassert(mc, mp->mp_pgno != pgno);
		mdb_midl_xappend(txn->mt_free_pgs, mp->mp_pgno);
		/* Update the parent page, if any, to point to the new page */
		if (mc->mc_top) {
			MDB_page *parent = mc->mc_pg[mc->mc_top-1];
			MDB_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)) {
		MDB_ID2 mid, *dl = txn->mt_u.dirty_list;
		pgno = mp->mp_pgno;
		/* If txn has a parent, make sure the page is in our
		 * dirty list.
		 */
		if (dl[0].mid) {
			unsigned x = mdb_mid2l_search(dl, pgno);
			if (x <= dl[0].mid && dl[x].mid == pgno) {
				if (unlikely(mp != dl[x].mptr)) { /* bad cursor? */
					mc->mc_flags &= ~(C_INITIALIZED|C_EOF);
					txn->mt_flags |= MDB_TXN_ERROR;
					return MDB_CORRUPTED;
				}
				return 0;
			}
		}
		mdb_cassert(mc, dl[0].mid < MDB_IDL_UM_MAX);
		/* No - copy it */
		np = mdb_page_malloc(txn, 1);
		if (unlikely(!np))
			return ENOMEM;
		mid.mid = pgno;
		mid.mptr = np;
		rc = mdb_mid2l_insert(dl, &mid);
		mdb_cassert(mc, rc == 0);
	} else {
		return 0;
	}

	mdb_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 ((mc->mc_db->md_flags & MDB_DUPSORT) &&
					IS_LEAF(np) &&
					(m2->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED))
				{
					MDB_node *leaf = NODEPTR(np, m2->mc_ki[mc->mc_top]);
					if ((leaf->mn_flags & (F_DUPDATA|F_SUBDATA)) == F_DUPDATA)
						m2->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
				}
			}
		}
	}
	return 0;

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

int
mdb_env_sync(MDB_env *env, int force)
{
	int rc;
	pthread_mutex_t *mutex;
	MDB_meta *head;
	unsigned flags;

	if (unlikely(! env))
		return EINVAL;

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

	if (unlikely(! env->me_txns))
		return MDB_PANIC;

	flags = env->me_flags & ~MDB_NOMETASYNC;
	if (unlikely(flags & (MDB_RDONLY | MDB_FATAL_ERROR)))
		return EACCES;

	head = mdb_meta_head_r(env);
	if (! META_IS_WEAK(head) && env->me_sync_pending == 0
			&& env->me_mapsize == head->mm_mapsize)
		/* LY: nothing to do */
		return MDB_SUCCESS;

	if (force || head->mm_mapsize != env->me_mapsize
			|| (env->me_sync_threshold && env->me_sync_pending >= env->me_sync_threshold))
		flags &= MDB_WRITEMAP;

	/* LY: early sync before acquiring the mutex to reduce writer's latency */
	if (env->me_sync_pending > env->me_psize * 16 && (flags & MDB_NOSYNC) == 0) {
		if (flags & MDB_WRITEMAP) {
			size_t used_size = env->me_psize * (head->mm_last_pg + 1);
			rc = msync(env->me_map, used_size,
					(flags & MDB_MAPASYNC) ? MS_ASYNC : MS_SYNC);
		} else {
			rc = fdatasync(env->me_fd);
		}
		if (unlikely(rc))
			return errno;
	}

	mutex = MDB_MUTEX(env, w);
	rc = mdb_mutex_lock(env, mutex);
	if (unlikely(rc))
		return rc;

	/* LY: head may be changed while the mutex has been acquired. */
	head = mdb_meta_head_w(env);
	rc = MDB_SUCCESS;
	if (META_IS_WEAK(head) || env->me_sync_pending != 0
			|| env->me_mapsize != head->mm_mapsize) {
		MDB_meta meta = *head;
		rc = mdb_env_sync0(env, flags, &meta);
	}

	mdb_mutex_unlock(env, mutex);
	return rc;
}

/** Back up parent txn's cursors, then grab the originals for tracking */
static int
mdb_cursor_shadow(MDB_txn *src, MDB_txn *dst)
{
	MDB_cursor *mc, *bk;
	MDB_xcursor *mx;
	size_t size;
	int i;

	for (i = src->mt_numdbs; --i >= 0; ) {
		if ((mc = src->mt_cursors[i]) != NULL) {
			size = sizeof(MDB_cursor);
			if (mc->mc_xcursor)
				size += sizeof(MDB_xcursor);
			for (; mc; mc = bk->mc_next) {
				bk = malloc(size);
				if (unlikely(!bk))
					return 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) {
					*(MDB_xcursor *)(bk+1) = *mx;
					mx->mx_cursor.mc_txn = dst;
				}
				mc->mc_next = dst->mt_cursors[i];
				dst->mt_cursors[i] = mc;
			}
		}
	}
	return MDB_SUCCESS;
}

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

	for (i = txn->mt_numdbs; --i >= 0; ) {
		for (mc = cursors[i]; mc; mc = next) {
			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 = *(MDB_xcursor *)(bk+1);
				}
				mc = bk;
			}
			/* Only malloced cursors are permanently tracked. */
			mc->mc_signature = 0;
			free(mc);
		}
		cursors[i] = NULL;
	}
}

/** Set or check a pid lock. Set returns 0 on success.
 * Check returns 0 if the process is certainly dead, nonzero if it may
 * be alive (the lock exists or an error happened so we do not know).
 */
static int
mdb_reader_pid(MDB_env *env, int op, pid_t pid)
{
	for (;;) {
		int rc;
		struct flock lock_info;
		memset(&lock_info, 0, sizeof(lock_info));
		lock_info.l_type = F_WRLCK;
		lock_info.l_whence = SEEK_SET;
		lock_info.l_start = pid;
		lock_info.l_len = 1;
		if ((rc = fcntl(env->me_lfd, op, &lock_info)) == 0) {
			if (op == F_GETLK && lock_info.l_type != F_UNLCK)
				rc = -1;
		} else if ((rc = errno) == EINTR) {
			continue;
		}
		return rc;
	}
}

/** Common code for #mdb_txn_begin() and #mdb_txn_renew().
 * @param[in] txn the transaction handle to initialize
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_txn_renew0(MDB_txn *txn, unsigned flags)
{
	MDB_env *env = txn->mt_env;
	unsigned i, nr;
	int rc, new_notls = 0;

	if (unlikely(env->me_pid != getpid())) {
		env->me_flags |= MDB_FATAL_ERROR;
		return MDB_PANIC;
	}

	if (flags & MDB_TXN_RDONLY) {
		struct MDB_rthc *rthc = NULL;
		MDB_reader *r = NULL;

		txn->mt_flags = MDB_TXN_RDONLY;
		if (likely(env->me_flags & MDB_ENV_TXKEY)) {
			mdb_assert(env, !(env->me_flags & MDB_NOTLS));
			rthc = pthread_getspecific(env->me_txkey);
			if (unlikely(! rthc)) {
				rthc = calloc(1, sizeof(struct MDB_rthc));
				if (unlikely(! rthc))
					return ENOMEM;
				rc = pthread_setspecific(env->me_txkey, rthc);
				if (unlikely(rc)) {
					free(rthc);
					return rc;
				}
			}
			r = rthc->rc_reader;
			if (r) {
				mdb_assert(env, r->mr_pid == env->me_pid);
				mdb_assert(env, r->mr_tid == pthread_self());
				mdb_assert(env, r->mr_rthc == rthc);
			}
		} else {
			mdb_assert(env, env->me_flags & MDB_NOTLS);
			r = txn->mt_u.reader;
		}

		if (likely(r)) {
			if (unlikely(r->mr_pid != env->me_pid || r->mr_txnid != ~(txnid_t)0))
				return MDB_BAD_RSLOT;
		} else {
			pid_t pid = env->me_pid;
			pthread_t tid = pthread_self();
			pthread_mutex_t *rmutex = MDB_MUTEX(env, r);

			rc = mdb_mutex_lock(env, rmutex);
			if (unlikely(rc != MDB_SUCCESS))
				return rc;

			if (unlikely(!env->me_live_reader)) {
				rc = mdb_reader_pid(env, F_SETLK, pid);
				if (unlikely(rc != MDB_SUCCESS)) {
					mdb_mutex_unlock(env, rmutex);
					return rc;
				}
				env->me_live_reader = 1;
			}

			nr = env->me_txns->mti_numreaders;
			for (i=0; i<nr; i++)
				if (env->me_txns->mti_readers[i].mr_pid == 0)
					break;
			if (unlikely(i == env->me_maxreaders)) {
				mdb_mutex_unlock(env, rmutex);
				return MDB_READERS_FULL;
			}
			r = &env->me_txns->mti_readers[i];
			/* Claim the reader slot, carefully since other code
			 * uses the reader table un-mutexed: First reset the
			 * slot, next publish it in mti_numreaders.  After
			 * that, it is safe for mdb_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;
			mdb_coherent_barrier();
#ifdef __SANITIZE_THREAD__
			pthread_mutex_lock(&tsan_mutex);
#endif
			if (i == nr)
				env->me_txns->mti_numreaders = ++nr;
			if (env->me_close_readers < nr)
				env->me_close_readers = nr;
			r->mr_pid = pid;
#ifdef __SANITIZE_THREAD__
			pthread_mutex_unlock(&tsan_mutex);
#endif
			mdb_mutex_unlock(env, rmutex);

			new_notls = MDB_END_SLOT;
			if (likely(rthc)) {
				rthc->rc_reader = r;
				r->mr_rthc = rthc;
				new_notls = 0;
			}
		}

		while((env->me_flags & MDB_FATAL_ERROR) == 0) {
			MDB_meta *meta = mdb_meta_head_r(txn->mt_env);
			txnid_t lead = meta->mm_txnid;
			r->mr_txnid = lead;
			mdb_coherent_barrier();

			txnid_t snap = txn->mt_env->me_txns->mti_txnid;
			/* LY: Retry on a race, ITS#7970. */
			if (likely(lead == snap)) {
				txn->mt_txnid = lead;
				txn->mt_next_pgno = meta->mm_last_pg+1;
				/* Copy the DB info and flags */
				memcpy(txn->mt_dbs, meta->mm_dbs, CORE_DBS * sizeof(MDB_db));
				break;
			}
		}

		txn->mt_u.reader = r;
		txn->mt_dbxs = env->me_dbxs;	/* mostly static anyway */
	} else {
		/* Not yet touching txn == env->me_txn0, it may be active */
		rc = mdb_mutex_lock(env, MDB_MUTEX(env, w));
		if (unlikely(rc))
			return rc;

#ifdef __SANITIZE_THREAD__
		pthread_mutex_lock(&tsan_mutex);
#endif
		MDB_meta *meta = mdb_meta_head_w(env);
		txn->mt_txnid = meta->mm_txnid + 1;
		txn->mt_flags = flags;
#ifdef __SANITIZE_THREAD__
		pthread_mutex_unlock(&tsan_mutex);
#endif

#if MDB_DEBUG
		if (unlikely(txn->mt_txnid == mdb_debug_edge)) {
			if (! mdb_debug_logger)
				mdb_runtime_flags |= MDB_DBG_TRACE | MDB_DBG_EXTRA
						| MDB_DBG_AUDIT | MDB_DBG_ASSERT;
			mdb_debug_log(MDB_DBG_EDGE, __FUNCTION__, __LINE__,
							 "on/off edge (txn %zu)", txn->mt_txnid);
		}
#endif
		txn->mt_child = NULL;
		txn->mt_loose_pgs = NULL;
		txn->mt_loose_count = 0;
		txn->mt_dirty_room = MDB_IDL_UM_MAX;
		txn->mt_u.dirty_list = env->me_dirty_list;
		txn->mt_u.dirty_list[0].mid = 0;
		txn->mt_free_pgs = env->me_free_pgs;
		txn->mt_free_pgs[0] = 0;
		txn->mt_spill_pgs = 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(MDB_db));
		/* Moved to here to avoid a data race in read TXNs */
		txn->mt_next_pgno = meta->mm_last_pg+1;
	}

	/* Setup db info */
	txn->mt_numdbs = env->me_numdbs;
	for (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 & MDB_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 & MDB_FATAL_ERROR)) {
		mdb_debug("environment had fatal error, must shutdown!");
		rc = MDB_PANIC;
	} else if (unlikely(env->me_maxpg < txn->mt_next_pgno)) {
		rc = MDB_MAP_RESIZED;
	} else {
		return MDB_SUCCESS;
	}
	mdb_txn_end(txn, new_notls /*0 or MDB_END_SLOT*/ | MDB_END_FAIL_BEGIN);
	return rc;
}

int
mdb_txn_renew(MDB_txn *txn)
{
	int rc;

	if (unlikely(!txn))
		return EINVAL;

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

	if (unlikely(!F_ISSET(txn->mt_flags, MDB_TXN_RDONLY|MDB_TXN_FINISHED)))
		return EINVAL;

	rc = mdb_txn_renew0(txn, MDB_TXN_RDONLY);
	if (rc == MDB_SUCCESS) {
		mdb_debug("renew txn %zu%c %p on mdbenv %p, root page %zu",
			txn->mt_txnid, (txn->mt_flags & MDB_TXN_RDONLY) ? 'r' : 'w',
			(void *)txn, (void *)txn->mt_env, txn->mt_dbs[MAIN_DBI].md_root);
	}
	return rc;
}

int
mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned flags, MDB_txn **ret)
{
	MDB_txn *txn;
	MDB_ntxn *ntxn;
	int rc, size, tsize;

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

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

	if (unlikely(env->me_pid != getpid())) {
		env->me_flags |= MDB_FATAL_ERROR;
		return MDB_PANIC;
	}

	flags &= MDB_TXN_BEGIN_FLAGS;
	flags |= env->me_flags & MDB_WRITEMAP;

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

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

		/* Nested transactions: Max 1 child, write txns only, no writemap */
		flags |= parent->mt_flags;
		if (unlikely(flags & (MDB_RDONLY|MDB_WRITEMAP|MDB_TXN_BLOCKED))) {
			return (parent->mt_flags & MDB_TXN_RDONLY) ? EINVAL : MDB_BAD_TXN;
		}
		/* Child txns save MDB_pgstate and use own copy of cursors */
		size = env->me_maxdbs * (sizeof(MDB_db)+sizeof(MDB_cursor *)+1);
		size += tsize = sizeof(MDB_ntxn);
	} else if (flags & MDB_RDONLY) {
		size = env->me_maxdbs * (sizeof(MDB_db)+1);
		size += tsize = sizeof(MDB_txn);
	} else {
		/* Reuse preallocated write txn. However, do not touch it until
		 * mdb_txn_renew0() succeeds, since it currently may be active.
		 */
		txn = env->me_txn0;
		goto renew;
	}
	if (unlikely((txn = calloc(1, size)) == NULL)) {
		mdb_debug("calloc: %s", strerror(errno));
		return ENOMEM;
	}
	txn->mt_dbxs = env->me_dbxs;	/* static */
	txn->mt_dbs = (MDB_db *) ((char *)txn + tsize);
	txn->mt_dbflags = (unsigned char *)txn + size - env->me_maxdbs;
	txn->mt_flags = flags;
	txn->mt_env = env;

	if (parent) {
		unsigned i;
		txn->mt_cursors = (MDB_cursor **)(txn->mt_dbs + env->me_maxdbs);
		txn->mt_dbiseqs = parent->mt_dbiseqs;
		txn->mt_u.dirty_list = malloc(sizeof(MDB_ID2)*MDB_IDL_UM_SIZE);
		if (!txn->mt_u.dirty_list ||
			!(txn->mt_free_pgs = mdb_midl_alloc(MDB_IDL_UM_MAX)))
		{
			free(txn->mt_u.dirty_list);
			free(txn);
			return ENOMEM;
		}
		txn->mt_txnid = parent->mt_txnid;
		txn->mt_dirty_room = parent->mt_dirty_room;
		txn->mt_u.dirty_list[0].mid = 0;
		txn->mt_spill_pgs = NULL;
		txn->mt_next_pgno = parent->mt_next_pgno;
		parent->mt_flags |= MDB_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(MDB_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 = (MDB_ntxn *)txn;
		ntxn->mnt_pgstate = env->me_pgstate; /* save parent me_pghead & co */
		if (env->me_pghead) {
			size = MDB_IDL_SIZEOF(env->me_pghead);
			env->me_pghead = mdb_midl_alloc(env->me_pghead[0]);
			if (likely(env->me_pghead))
				memcpy(env->me_pghead, ntxn->mnt_pgstate.mf_pghead, size);
			else
				rc = ENOMEM;
		}
		if (likely(!rc))
			rc = mdb_cursor_shadow(parent, txn);
		if (unlikely(rc))
			mdb_txn_end(txn, MDB_END_FAIL_BEGINCHILD);
	} else { /* MDB_RDONLY */
		txn->mt_dbiseqs = env->me_dbiseqs;
renew:
		rc = mdb_txn_renew0(txn, flags);
	}
	if (unlikely(rc)) {
		if (txn != env->me_txn0)
			free(txn);
	} else {
		txn->mt_signature = MDBX_MT_SIGNATURE;
		*ret = txn;
		mdb_debug("begin txn %zu%c %p on mdbenv %p, root page %zu",
			txn->mt_txnid, (flags & MDB_RDONLY) ? 'r' : 'w',
			(void *) txn, (void *) env, txn->mt_dbs[MAIN_DBI].md_root);
	}

	return rc;
}

MDB_env *
mdb_txn_env(MDB_txn *txn)
{
	if(unlikely(!txn || txn->mt_signature != MDBX_MT_SIGNATURE))
		return NULL;
	return txn->mt_env;
}

size_t
mdb_txn_id(MDB_txn *txn)
{
	if(unlikely(!txn || txn->mt_signature != MDBX_MT_SIGNATURE))
		return 0;
	return txn->mt_txnid;
}

/** Export or close DBI handles opened in this txn. */
static void
mdb_dbis_update(MDB_txn *txn, int keep)
{
	int i;
	MDB_dbi n = txn->mt_numdbs;
	MDB_env *env = txn->mt_env;
	unsigned char *tdbflags = txn->mt_dbflags;

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

ATTRIBUTE_NO_SANITIZE_THREAD /* LY: avoid tsan-trap by me_txn, mm_last_pg and mt_next_pgno */
int mdbx_txn_straggler(MDB_txn *txn, int *percent)
{
	MDB_env	*env;
	MDB_meta *meta;
	txnid_t lag;

	if(unlikely(!txn))
		return -EINVAL;

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

	if (unlikely(! txn->mt_u.reader))
		return -1;

	env = txn->mt_env;
	meta = mdb_meta_head_r(env);
	if (percent) {
		size_t maxpg = env->me_maxpg;
		size_t last = meta->mm_last_pg + 1;
		if (env->me_txn)
			last = env->me_txn0->mt_next_pgno;
		*percent = (last * 100ull + maxpg / 2) / maxpg;
	}
	lag = meta->mm_txnid - txn->mt_u.reader->mr_txnid;
	return (0 > (long) lag) ? ~0u >> 1: lag;
}

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

	if (unlikely(txn->mt_env->me_pid != getpid())) {
		env->me_flags |= MDB_FATAL_ERROR;
		return MDB_PANIC;
	}

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

	mdb_debug("%s txn %zu%c %p on mdbenv %p, root page %zu",
		names[mode & MDB_END_OPMASK],
		txn->mt_txnid, (txn->mt_flags & MDB_TXN_RDONLY) ? 'r' : 'w',
		(void *) txn, (void *)env, txn->mt_dbs[MAIN_DBI].md_root);

	if (F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)) {
		if (txn->mt_u.reader) {
#ifdef __SANITIZE_THREAD__
			pthread_mutex_lock(&tsan_mutex);
#endif
			txn->mt_u.reader->mr_txnid = ~(txnid_t)0;
			if (!(env->me_flags & MDB_NOTLS)) {
				txn->mt_u.reader = NULL; /* txn does not own reader */
			} else if (mode & MDB_END_SLOT) {
				txn->mt_u.reader->mr_pid = 0;
				txn->mt_u.reader = NULL;
			} /* else txn owns the slot until it does MDB_END_SLOT */
#ifdef __SANITIZE_THREAD__
			pthread_mutex_unlock(&tsan_mutex);
#endif
		}
		mdb_coherent_barrier();
		txn->mt_numdbs = 0;		/* prevent further DBI activity */
		txn->mt_flags |= MDB_TXN_FINISHED;

	} else if (!F_ISSET(txn->mt_flags, MDB_TXN_FINISHED)) {
		pgno_t *pghead = env->me_pghead;

		if (!(mode & MDB_END_UPDATE)) /* !(already closed cursors) */
			mdb_cursors_close(txn, 0);
		if (!(env->me_flags & MDB_WRITEMAP)) {
			mdb_dlist_free(txn);
		}

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

		if (!txn->mt_parent) {
			mdb_midl_shrink(&txn->mt_free_pgs);
			env->me_free_pgs = txn->mt_free_pgs;
			/* me_pgstate: */
			env->me_pghead = NULL;
			env->me_pglast = 0;

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

			/* The writer mutex was locked in mdb_txn_begin. */
			mdb_mutex_unlock(env, MDB_MUTEX(env, w));
		} else {
			txn->mt_parent->mt_child = NULL;
			txn->mt_parent->mt_flags &= ~MDB_TXN_HAS_CHILD;
			env->me_pgstate = ((MDB_ntxn *)txn)->mnt_pgstate;
			mdb_midl_free(txn->mt_free_pgs);
			mdb_midl_free(txn->mt_spill_pgs);
			free(txn->mt_u.dirty_list);
		}

		mdb_midl_free(pghead);
	}

	if (mode & MDB_END_FREE) {
		txn->mt_signature = 0;
		free(txn);
	}

	return MDB_SUCCESS;
}

int
mdb_txn_reset(MDB_txn *txn)
{
	if (unlikely(! txn))
		return EINVAL;

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

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

	return mdb_txn_end(txn, MDB_END_RESET);
}

int
mdb_txn_abort(MDB_txn *txn)
{
	if (unlikely(! txn))
		return EINVAL;

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

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

	return mdb_txn_end(txn, MDB_END_ABORT|MDB_END_SLOT|MDB_END_FREE);
}

static MDB_INLINE int
mdb_backlog_size(MDB_txn *txn)
{
	int reclaimed = txn->mt_env->me_pghead ? txn->mt_env->me_pghead[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 mdb_page_alloc() during a deleting, when freeDB tree is unbalanced. */
static int
mdb_prep_backlog(MDB_txn *txn, MDB_cursor *mc)
{
	if (mdb_backlog_size(txn) <= mc->mc_db->md_depth) {
		int rc = mdb_cursor_touch(mc);
		if (unlikely(rc))
			return rc;

		/* LY: one more page is required if a b-tree needs rebalancing */
		if (unlikely(mdb_backlog_size(txn) < 1)) {
			rc = mdb_page_alloc(mc, 1, NULL, MDB_ALLOC_GC);
			if (unlikely(rc && rc != MDB_NOTFOUND))
				return rc;
		}
	}

	return MDB_SUCCESS;
}

/** Save the freelist as of this transaction to the freeDB.
 * This changes the freelist. Keep trying until it stabilizes.
 */
static int
mdb_freelist_save(MDB_txn *txn)
{
	/* env->me_pghead[] can grow and shrink during this call.
	 * env->me_pglast and txn->mt_free_pgs[] can only grow.
	 * Page numbers cannot disappear from txn->mt_free_pgs[].
	 */
	MDB_cursor mc;
	MDB_env	*env = txn->mt_env;
	int rc, maxfree_1pg = env->me_maxfree_1pg, more = 1;
	txnid_t	pglast = 0, head_id = 0;
	pgno_t	freecnt = 0, *free_pgs, *mop;
	ssize_t	head_room = 0, total_room = 0, mop_len, clean_limit;
	unsigned cleanup_idx = 0, refill_idx = 0;
	const int lifo = (env->me_flags & MDB_LIFORECLAIM) != 0;

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

	/* MDB_RESERVE cancels meminit in ovpage malloc (when no WRITEMAP) */
	clean_limit = (env->me_flags & (MDB_NOMEMINIT|MDB_WRITEMAP))
		? SSIZE_MAX : maxfree_1pg;

again:
	for (;;) {
		/* Come back here after each Put() in case freelist changed */
		MDB_val key, data;
		pgno_t *pgs;
		ssize_t j;

		if (! lifo) {
			/* If using records from freeDB which we have not yet
			 * deleted, delete them and any we reserved for me_pghead.
			 */
			while (pglast < env->me_pglast) {
				rc = mdb_cursor_first(&mc, &key, NULL);
				if (unlikely(rc))
					goto bailout;
				rc = mdb_prep_backlog(txn, &mc);
				if (unlikely(rc))
					goto bailout;
				pglast = head_id = *(txnid_t *)key.mv_data;
				total_room = head_room = 0;
				more = 1;
				mdb_tassert(txn, pglast <= env->me_pglast);
				mc.mc_flags |= C_RECLAIMING;
				rc = mdb_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_idx < txn->mt_lifo_reclaimed[0]) {
				pglast = txn->mt_lifo_reclaimed[++cleanup_idx];
				key.mv_data = &pglast;
				key.mv_size = sizeof(pglast);
				rc = mdb_cursor_get(&mc, &key, NULL, MDB_SET);
				if (likely(rc != MDB_NOTFOUND)) {
					if (unlikely(rc))
						goto bailout;
					rc = mdb_prep_backlog(txn, &mc);
					if (unlikely(rc))
						goto bailout;
					mc.mc_flags |= C_RECLAIMING;
					rc = mdb_cursor_del(&mc, 0);
					mc.mc_flags &= ~C_RECLAIMING;
					if (unlikely(rc))
						goto bailout;
				}
			}
		}

		if (unlikely(!env->me_pghead) && txn->mt_loose_pgs) {
			/* Put loose page numbers in mt_free_pgs, since
			 * we may be unable to return them to me_pghead.
			 */
			MDB_page *mp = txn->mt_loose_pgs;
			if (unlikely((rc = mdb_midl_need(&txn->mt_free_pgs, txn->mt_loose_count)) != 0))
				return rc;
			for (; mp; mp = NEXT_LOOSE_PAGE(mp))
				mdb_midl_xappend(txn->mt_free_pgs, mp->mp_pgno);
			txn->mt_loose_pgs = NULL;
			txn->mt_loose_count = 0;
		}

		/* Save the IDL of pages freed by this txn, to a single record */
		if (freecnt < txn->mt_free_pgs[0]) {
			if (unlikely(!freecnt)) {
				/* Make sure last page of freeDB is touched and on freelist */
				rc = mdb_page_search(&mc, NULL, MDB_PS_LAST|MDB_PS_MODIFY);
				if (unlikely(rc && rc != MDB_NOTFOUND))
					goto bailout;
			}
			free_pgs = txn->mt_free_pgs;
			/* Write to last page of freeDB */
			key.mv_size = sizeof(txn->mt_txnid);
			key.mv_data = &txn->mt_txnid;
			do {
				freecnt = free_pgs[0];
				data.mv_size = MDB_IDL_SIZEOF(free_pgs);
				rc = mdb_cursor_put(&mc, &key, &data, MDB_RESERVE);
				if (unlikely(rc))
					goto bailout;
				/* Retry if mt_free_pgs[] grew during the Put() */
				free_pgs = txn->mt_free_pgs;
			} while (freecnt < free_pgs[0]);

			mdb_midl_sort(free_pgs);
			memcpy(data.mv_data, free_pgs, data.mv_size);

			if (mdb_debug_enabled(MDB_DBG_EXTRA)) {
				unsigned i = free_pgs[0];
				mdb_debug_extra("IDL write txn %zu root %zu num %u, IDL",
					txn->mt_txnid, txn->mt_dbs[FREE_DBI].md_root, i);
				for (; i; i--)
					mdb_debug_extra_print(" %zu", free_pgs[i]);
				mdb_debug_extra_print("\n");
			}
			continue;
		}

		mop = env->me_pghead;
		mop_len = (mop ? mop[0] : 0) + txn->mt_loose_count;

		if (mop_len && refill_idx == 0)
			refill_idx = 1;

		/* Reserve records for me_pghead[]. Split it if multi-page,
		 * to avoid searching freeDB for a page range. Use keys in
		 * range [1,me_pglast]: Smaller than txnid of oldest reader.
		 */
		if (total_room >= mop_len) {
			if (total_room == mop_len || --more < 0)
				break;
		} else if (head_room >= maxfree_1pg && head_id > 1) {
			/* Keep current record (overflow page), add a new one */
			head_id--;
			refill_idx++;
			head_room = 0;
		}

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

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

				if (unlikely(! txn->mt_lifo_reclaimed)) {
					txn->mt_lifo_reclaimed = mdb_midl_alloc(env->me_maxfree_1pg);
					if (unlikely(! txn->mt_lifo_reclaimed)) {
						rc = ENOMEM;
						goto bailout;
					}
				}
				/* LY: append the list. */
				rc = mdb_midl_append(&txn->mt_lifo_reclaimed, env->me_pglast - 1);
				if (unlikely(rc))
					goto bailout;
				--env->me_pglast;
				/* LY: note that freeDB cleanup is not needed. */
				++cleanup_idx;
			}
			head_id = txn->mt_lifo_reclaimed[refill_idx];
		}

		/* (Re)write {key = head_id, IDL length = head_room} */
		total_room -= head_room;
		head_room = mop_len - total_room;
		if (head_room > maxfree_1pg && head_id > 1) {
			/* Overflow multi-page for part of me_pghead */
			head_room /= head_id; /* amortize page sizes */
			head_room += maxfree_1pg - head_room % (maxfree_1pg + 1);
		} else if (head_room < 0) {
			/* Rare case, not bothering to delete this record */
			head_room = 0;
			continue;
		}
		key.mv_size = sizeof(head_id);
		key.mv_data = &head_id;
		data.mv_size = (head_room + 1) * sizeof(pgno_t);
		rc = mdb_cursor_put(&mc, &key, &data, MDB_RESERVE);
		if (unlikely(rc))
			goto bailout;
		/* IDL is initially empty, zero out at least the length */
		pgs = (pgno_t *)data.mv_data;
		j = head_room > clean_limit ? head_room : 0;
		do {
			pgs[j] = 0;
		} while (--j >= 0);
		total_room += head_room;
	}

	mdb_tassert(txn, cleanup_idx == (txn->mt_lifo_reclaimed ? txn->mt_lifo_reclaimed[0] : 0));

	/* Return loose page numbers to me_pghead, though usually none are
	 * left at this point.  The pages themselves remain in dirty_list.
	 */
	if (txn->mt_loose_pgs) {
		MDB_page *mp = txn->mt_loose_pgs;
		unsigned count = txn->mt_loose_count;
		MDB_IDL loose;
		/* Room for loose pages + temp IDL with same */
		if ((rc = mdb_midl_need(&env->me_pghead, 2*count+1)) != 0)
			goto bailout;
		mop = env->me_pghead;
		loose = mop + MDB_IDL_ALLOCLEN(mop) - count;
		for (count = 0; mp; mp = NEXT_LOOSE_PAGE(mp))
			loose[ ++count ] = mp->mp_pgno;
		loose[0] = count;
		mdb_midl_sort(loose);
		mdb_midl_xmerge(mop, loose);
		txn->mt_loose_pgs = NULL;
		txn->mt_loose_count = 0;
		mop_len = mop[0];
	}

	/* Fill in the reserved me_pghead records */
	rc = MDB_SUCCESS;
	if (mop_len) {
		MDB_val key, data;

		mop += mop_len;
		if (! lifo) {
			rc = mdb_cursor_first(&mc, &key, &data);
			if (unlikely(rc))
				goto bailout;
		}

		for(;;) {
			txnid_t id;
			ssize_t	len;
			MDB_ID save;

			if (! lifo) {
				id = *(txnid_t *)key.mv_data;
				mdb_tassert(txn, id <= env->me_pglast);
			} else {
				mdb_tassert(txn, refill_idx > 0 && refill_idx <= txn->mt_lifo_reclaimed[0]);
				id = txn->mt_lifo_reclaimed[refill_idx--];
				key.mv_data = &id;
				key.mv_size = sizeof(id);
				rc = mdb_cursor_get(&mc, &key, &data, MDB_SET);
				if (unlikely(rc))
					goto bailout;
			}
			mdb_tassert(txn, cleanup_idx == (txn->mt_lifo_reclaimed ? txn->mt_lifo_reclaimed[0] : 0));

			len = (ssize_t)(data.mv_size / sizeof(MDB_ID)) - 1;
			mdb_tassert(txn, len >= 0);
			if (len > mop_len)
				len = mop_len;
			data.mv_size = (len + 1) * sizeof(MDB_ID);
			key.mv_data = &id;
			key.mv_size = sizeof(id);
			data.mv_data = mop -= len;

			save = mop[0];
			mop[0] = len;
			rc = mdb_cursor_put(&mc, &key, &data, MDB_CURRENT);
			mdb_tassert(txn, cleanup_idx == (txn->mt_lifo_reclaimed ? txn->mt_lifo_reclaimed[0] : 0));
			mop[0] = save;
			if (unlikely(rc || (mop_len -= len) == 0))
				goto bailout;

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

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

	return rc;
}

/** Flush (some) dirty pages to the map, after clearing their dirty flag.
 * @param[in] txn the transaction that's being committed
 * @param[in] keep number of initial pages in dirty_list to keep dirty.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_flush(MDB_txn *txn, int keep)
{
	MDB_env		*env = txn->mt_env;
	MDB_ID2L	dl = txn->mt_u.dirty_list;
	unsigned	psize = env->me_psize, j;
	int			i, pagecount = dl[0].mid, rc;
	size_t		size = 0, pos = 0;
	pgno_t		pgno = 0;
	MDB_page	*dp = NULL;
	struct iovec iov[MDB_COMMIT_PAGES];
	ssize_t		wpos = 0, wsize = 0, wres;
	size_t		next_pos = 1; /* impossible pos, so pos != next_pos */
	int			n = 0;

	j = i = keep;

	if (env->me_flags & MDB_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;
			env->me_sync_pending += IS_OVERFLOW(dp) ? psize * dp->mp_pages : 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;
			pos = pgno * psize;
			size = psize;
			if (IS_OVERFLOW(dp)) size *= dp->mp_pages;
			env->me_sync_pending += size;
		}
		/* Write up to MDB_COMMIT_PAGES dirty pages at a time. */
		if (pos!=next_pos || n==MDB_COMMIT_PAGES || wsize+size>MAX_WRITE) {
			if (n) {
retry:
				/* Write previous page(s) */
				wres = pwritev(env->me_fd, iov, n, wpos);
				if (unlikely(wres != wsize)) {
					if (wres < 0) {
						rc = errno;
						if (rc == EINTR)
							goto retry;
						mdb_debug("Write error: %s", strerror(rc));
					} else {
						rc = EIO; /* TODO: Use which error code? */
						mdb_debug("short write, filesystem full?");
					}
					return rc;
				}
				n = 0;
			}
			if (i > pagecount)
				break;
			wpos = pos;
			wsize = 0;
		}
		mdb_debug("committing page %zu", pgno);
		next_pos = pos + size;
		iov[n].iov_len = size;
		iov[n].iov_base = (char *)dp;
		wsize += size;
		n++;
	}

	mdb_invalidate_cache(env->me_map, txn->mt_next_pgno * env->me_psize);

	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;
		}
		mdb_dpage_free(env, dp);
	}

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

int
mdb_txn_commit(MDB_txn *txn)
{
	int rc;
	unsigned i, end_mode;
	MDB_env	*env;

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

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

	if (unlikely(txn->mt_env->me_pid != getpid())) {
		txn->mt_env->me_flags |= MDB_FATAL_ERROR;
		return MDB_PANIC;
	}

	/* mdb_txn_end() mode for a commit which writes nothing */
	end_mode = MDB_END_EMPTY_COMMIT|MDB_END_UPDATE|MDB_END_SLOT|MDB_END_FREE;

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

	env = txn->mt_env;

	if (unlikely(F_ISSET(txn->mt_flags, MDB_TXN_RDONLY))) {
		goto done;
	}

	if (unlikely(txn->mt_flags & (MDB_TXN_FINISHED|MDB_TXN_ERROR))) {
		mdb_debug("error flag is set, can't commit");
		if (txn->mt_parent)
			txn->mt_parent->mt_flags |= MDB_TXN_ERROR;
		rc = MDB_BAD_TXN;
		goto fail;
	}

	if (txn->mt_parent) {
		MDB_txn *parent = txn->mt_parent;
		MDB_page **lp;
		MDB_ID2L dst, src;
		MDB_IDL pspill;
		unsigned x, y, len, ps_len;

		/* Append our reclaim list to parent's */
		if (txn->mt_lifo_reclaimed) {
			if (parent->mt_lifo_reclaimed) {
				rc = mdb_midl_append_list(&parent->mt_lifo_reclaimed, txn->mt_lifo_reclaimed);
				if (unlikely(rc != MDB_SUCCESS))
					goto fail;
				mdb_midl_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 = mdb_midl_append_list(&parent->mt_free_pgs, txn->mt_free_pgs);
		if (unlikely(rc != MDB_SUCCESS))
			goto fail;
		mdb_midl_free(txn->mt_free_pgs);
		/* Failures after this must either undo the changes
		 * to the parent or set MDB_TXN_ERROR in the parent.
		 */

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

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

		/* Update parent's DB table. */
		memcpy(parent->mt_dbs, txn->mt_dbs, txn->mt_numdbs * sizeof(MDB_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 */
			x = parent->mt_dbflags[i] & DB_NEW;
			parent->mt_dbflags[i] = txn->mt_dbflags[i] | x;
		}

		dst = parent->mt_u.dirty_list;
		src = txn->mt_u.dirty_list;
		/* Remove anything in our dirty list from parent's spill list */
		if ((pspill = parent->mt_spill_pgs) && (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; ) {
				MDB_ID 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_pgs && txn->mt_spill_pgs[0]) {
			for (i=1; i<=txn->mt_spill_pgs[0]; i++) {
				MDB_ID pn = txn->mt_spill_pgs[i];
				if (pn & 1)
					continue;	/* deleted spillpg */
				pn >>= 1;
				y = mdb_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 = mdb_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 = MDB_IDL_UM_MAX - txn->mt_dirty_room;
		}
		/* 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);
		}
		mdb_tassert(txn, i == x);
		dst[0].mid = len;
		free(txn->mt_u.dirty_list);
		parent->mt_dirty_room = txn->mt_dirty_room;
		if (txn->mt_spill_pgs) {
			if (parent->mt_spill_pgs) {
				/* TODO: Prevent failure here, so parent does not fail */
				rc = mdb_midl_append_list(&parent->mt_spill_pgs, txn->mt_spill_pgs);
				if (unlikely(rc != MDB_SUCCESS))
					parent->mt_flags |= MDB_TXN_ERROR;
				mdb_midl_free(txn->mt_spill_pgs);
				mdb_midl_sort(parent->mt_spill_pgs);
			} else {
				parent->mt_spill_pgs = txn->mt_spill_pgs;
			}
		}

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

		parent->mt_child = NULL;
		mdb_midl_free(((MDB_ntxn *)txn)->mnt_pgstate.mf_pghead);
		txn->mt_signature = 0;
		free(txn);
		return rc;
	}

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

	mdb_cursors_close(txn, 0);

	if (!txn->mt_u.dirty_list[0].mid &&
		!(txn->mt_flags & (MDB_TXN_DIRTY|MDB_TXN_SPILLS)))
		goto done;

	mdb_debug("committing txn %zu %p on mdbenv %p, root page %zu",
		txn->mt_txnid, (void*)txn, (void*)env, txn->mt_dbs[MAIN_DBI].md_root);

	/* Update DB root pointers */
	if (txn->mt_numdbs > CORE_DBS) {
		MDB_cursor mc;
		MDB_dbi i;
		MDB_val data;
		data.mv_size = sizeof(MDB_db);

		mdb_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 = MDB_BAD_DBI;
					goto fail;
				}
				data.mv_data = &txn->mt_dbs[i];
				rc = mdb_cursor_put(&mc, &txn->mt_dbxs[i].md_name, &data,
					F_SUBDATA);
				if (unlikely(rc != MDB_SUCCESS))
					goto fail;
			}
		}
	}

	rc = mdb_freelist_save(txn);
	if (unlikely(rc != MDB_SUCCESS))
		goto fail;

	mdb_midl_free(env->me_pghead);
	env->me_pghead = NULL;
	mdb_midl_shrink(&txn->mt_free_pgs);

	if (mdb_audit_enabled())
		mdb_audit(txn);

	rc = mdb_page_flush(txn, 0);
	if (likely(rc == MDB_SUCCESS)) {
		MDB_meta meta;

		meta.mm_dbs[FREE_DBI] = txn->mt_dbs[FREE_DBI];
		meta.mm_dbs[MAIN_DBI] = txn->mt_dbs[MAIN_DBI];
		meta.mm_last_pg = txn->mt_next_pgno - 1;
		meta.mm_txnid = txn->mt_txnid;

		rc = mdb_env_sync0(env, env->me_flags | txn->mt_flags, &meta);
	}
	if (unlikely(rc != MDB_SUCCESS))
		goto fail;
	end_mode = MDB_END_COMMITTED|MDB_END_UPDATE;

done:
	return mdb_txn_end(txn, end_mode);

fail:
	mdb_txn_abort(txn);
	return rc;
}

#if MDBX_MODE_ENABLED
int __cold
mdbx_env_set_syncbytes(MDB_env *env, size_t bytes)
{
	if (unlikely(!env))
		return EINVAL;

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

	env->me_sync_threshold = bytes;
	return env->me_map ? mdb_env_sync(env, 0) : 0;
}
#endif /* MDBX_MODE_ENABLED */

/** Read the environment parameters of a DB environment before
 * mapping it into memory.
 * @param[in] env the environment handle
 * @param[out] meta address of where to store the meta information
 * @return 0 on success, non-zero on failure.
 */
static int __cold
mdb_env_read_header(MDB_env *env, MDB_meta *meta)
{
	MDB_metabuf	pbuf;
	MDB_page	*p;
	MDB_meta	*m;
	int			i, rc, off;
	enum { Size = sizeof(pbuf) };

	/* We don't know the page size yet, so use a minimum value.
	 * Read both meta pages so we can use the latest one.
	 */

	meta->mm_datasync_sign = MDB_DATASIGN_WEAK;
	meta->mm_txnid = 0;
	for (i=off=0; i<NUM_METAS; i++, off += meta->mm_psize) {
		rc = pread(env->me_fd, &pbuf, Size, off);
		if (rc != Size) {
			if (rc == 0 && off == 0)
				return ENOENT;
			rc = rc < 0 ? (int) errno : MDB_INVALID;
			mdb_debug("read: %s", mdb_strerror(rc));
			return rc;
		}

		p = (MDB_page *)&pbuf;

		if (!F_ISSET(p->mp_flags, P_META)) {
			mdb_debug("page %zu not a meta page", p->mp_pgno);
			return MDB_INVALID;
		}

		m = PAGEDATA(p);
		if (m->mm_magic != MDB_MAGIC) {
			mdb_debug("meta has invalid magic");
			return MDB_INVALID;
		}

		if (m->mm_version != MDB_DATA_VERSION) {
			mdb_debug("database is version %u, expected version %u",
				m->mm_version, MDB_DATA_VERSION);
			return MDB_VERSION_MISMATCH;
		}

		if (m->mm_datasync_sign > MDB_DATASIGN_WEAK && m->mm_datasync_sign != mdb_meta_sign(m))
			continue;

		if (mdb_meta_lt(meta, m))
			*meta = *m;
	}

	if (meta->mm_datasync_sign == MDB_DATASIGN_WEAK)
		/* LY: Both meta-pages are weak. */
		return MDB_CORRUPTED;

	return MDB_SUCCESS;
}

/** Fill in most of the zeroed #MDB_meta for an empty database environment */
static void __cold
mdb_env_init_meta0(MDB_env *env, MDB_meta *meta)
{
	meta->mm_magic = MDB_MAGIC;
	meta->mm_version = MDB_DATA_VERSION;
	meta->mm_mapsize = env->me_mapsize;
	meta->mm_psize = env->me_psize;
	meta->mm_last_pg = NUM_METAS-1;
	meta->mm_flags = env->me_flags & 0xffff;
	meta->mm_flags |= MDB_INTEGERKEY; /* this is mm_dbs[FREE_DBI].md_flags */
	meta->mm_dbs[FREE_DBI].md_root = P_INVALID;
	meta->mm_dbs[MAIN_DBI].md_root = P_INVALID;
	meta->mm_datasync_sign = mdb_meta_sign(meta);
}

/** Write the environment parameters of a freshly created DB environment.
 * @param[in] env the environment handle
 * @param[in] meta the #MDB_meta to write
 * @return 0 on success, non-zero on failure.
 */
static int __cold
mdb_env_init_meta(MDB_env *env, MDB_meta *meta)
{
	MDB_page *p, *q;
	int rc;
	unsigned psize;
	int len;

	mdb_debug("writing new meta page");

	psize = env->me_psize;

	p = calloc(NUM_METAS, psize);
	if (!p)
		return ENOMEM;
	p->mp_pgno = 0;
	p->mp_flags = P_META;
	*(MDB_meta *)PAGEDATA(p) = *meta;

	q = (MDB_page *)((char *)p + psize);
	q->mp_pgno = 1;
	q->mp_flags = P_META;
	*(MDB_meta *)PAGEDATA(q) = *meta;

	do
		len = pwrite(env->me_fd, p, psize * NUM_METAS, 0);
	while (len == -1 && errno == EINTR);

	if (len < 0)
		rc = errno;
	else if ((unsigned) len == psize * NUM_METAS)
		rc = MDB_SUCCESS;
	else
		rc = ENOSPC;
	free(p);
	return rc;
}

static int
mdb_env_sync0(MDB_env *env, unsigned flags, MDB_meta *pending)
{
	int rc;
	MDB_meta* head = mdb_meta_head_w(env);
	size_t prev_mapsize = head->mm_mapsize;
	volatile MDB_meta* target = META_IS_WEAK(head) ? head : mdb_env_meta_flipflop(env, head);
	off_t offset = (char*) target - env->me_map;
	size_t used_size = env->me_psize * (pending->mm_last_pg + 1);

	mdb_assert(env, (env->me_flags & (MDB_RDONLY | MDB_FATAL_ERROR)) == 0);
	mdb_assert(env, META_IS_WEAK(head) || env->me_sync_pending != 0
			   || env->me_mapsize != prev_mapsize);
	mdb_assert(env, pending->mm_txnid > head->mm_txnid || META_IS_WEAK(head));
	mdb_assert(env, pending->mm_txnid > target->mm_txnid || META_IS_WEAK(target));

	MDB_meta* stay = mdb_env_meta_flipflop(env, (MDB_meta*) target);
	mdb_assert(env, pending->mm_txnid > stay->mm_txnid);

	pending->mm_mapsize = env->me_mapsize;
	mdb_assert(env, pending->mm_mapsize >= used_size);
	if (unlikely(pending->mm_mapsize != prev_mapsize)) {
		if (pending->mm_mapsize < prev_mapsize) {
			/* LY: currently this can't happen, but force full-sync. */
			flags &= MDB_WRITEMAP;
		} else {
			/* Persist any increases of mapsize config */
		}
	}

	if (env->me_sync_threshold && env->me_sync_pending >= env->me_sync_threshold)
		flags &= MDB_WRITEMAP;

	/* LY: step#1 - sync previously written/updated data-pages */
	if (env->me_sync_pending && (flags & MDB_NOSYNC) == 0) {
		if (env->me_flags & MDB_WRITEMAP) {
			int mode = (flags & MDB_MAPASYNC) ? MS_ASYNC : MS_SYNC;
			if (unlikely(msync(env->me_map, used_size, mode))) {
				rc = errno;
				goto fail;
			}
			if ((flags & MDB_MAPASYNC) == 0)
				env->me_sync_pending = 0;
		} else {
			int (*flush)(int fd) = fdatasync;
			if (unlikely(prev_mapsize != pending->mm_mapsize)) {
				/* LY: It is no reason to use fdatasync() here, even in case
				 * no such bug in a kernel. Because "no-bug" mean that a kernel
				 * internally do nearly the same, e.g. fdatasync() == fsync()
				 * when no-kernel-bug and file size was changed.
				 *
				 * So, this code is always safe and without appreciable
				 * performance degradation.
				 *
				 * For more info about of a corresponding fdatasync() bug
				 * see http://www.spinics.net/lists/linux-ext4/msg33714.html */
				flush = fsync;
			}
			while(unlikely(flush(env->me_fd) < 0)) {
				rc = errno;
				if (rc != EINTR)
					goto undo;
			}
			env->me_sync_pending = 0;
		}
	}

	/* LY: step#2 - update meta-page. */
	if (env->me_sync_pending == 0) {
		pending->mm_datasync_sign = mdb_meta_sign(pending);
	} else {
		pending->mm_datasync_sign =
			(flags & MDB_UTTERLY_NOSYNC) == MDB_UTTERLY_NOSYNC
				? MDB_DATASIGN_NONE : MDB_DATASIGN_WEAK;
	}
	mdb_debug("writing meta %d, root %zu, txn_id %zu, %s",
		offset >= env->me_psize, pending->mm_dbs[MAIN_DBI].md_root,
		pending->mm_txnid,
		META_IS_WEAK(pending) ? "Weak" : META_IS_STEADY(pending) ? "Steady" : "Legacy" );

	if (env->me_flags & MDB_WRITEMAP) {
#ifdef __SANITIZE_THREAD__
		pthread_mutex_lock(&tsan_mutex);
#endif
		/* LY: 'invalidate' the meta,
		 * but mdb_meta_head_r() will be confused/retired in collision case. */
		target->mm_datasync_sign = MDB_DATASIGN_WEAK;
		target->mm_txnid = 0;
		/* LY: update info */
		target->mm_mapsize = pending->mm_mapsize;
		target->mm_dbs[FREE_DBI] = pending->mm_dbs[FREE_DBI];
		target->mm_dbs[MAIN_DBI] = pending->mm_dbs[MAIN_DBI];
		target->mm_last_pg = pending->mm_last_pg;
		/* LY: 'commit' the meta */
		target->mm_txnid = pending->mm_txnid;
		target->mm_datasync_sign = pending->mm_datasync_sign;
	} else {
		pending->mm_magic = MDB_MAGIC;
		pending->mm_version = MDB_DATA_VERSION;
		pending->mm_address = head->mm_address;
	retry:
		rc = pwrite(env->me_fd, pending, sizeof(MDB_meta), offset);
		if (unlikely(rc != sizeof(MDB_meta))) {
			rc = (rc < 0) ? errno : EIO;
			if (rc == EINTR)
				goto retry;

	undo:
			mdb_debug("write failed, disk error?");
			/* On a failure, the pagecache still contains the new data.
			 * Write some old data back, to prevent it from being used. */
			if (pwrite(env->me_fd, (void*) target, sizeof(MDB_meta), offset) == sizeof(MDB_meta)) {
				/* LY: take a chance, if write succeeds at a magic ;) */
				goto retry;
			}
			goto fail;
		}
		mdb_invalidate_cache(env->me_map + offset, sizeof(MDB_meta));
#ifdef __SANITIZE_THREAD__
		pthread_mutex_lock(&tsan_mutex);
#endif
	}

	/* Memory ordering issues are irrelevant; since the entire writer
	 * is wrapped by wmutex, all of these changes will become visible
	 * after the wmutex is unlocked. Since the DB is multi-version,
	 * readers will get consistent data regardless of how fresh or
	 * how stale their view of these values is.
	 */
	env->me_txns->mti_txnid = pending->mm_txnid;
#ifdef __SANITIZE_THREAD__
	pthread_mutex_unlock(&tsan_mutex);
#endif

	/* LY: step#3 - sync meta-pages. */
	if ((flags & (MDB_NOSYNC | MDB_NOMETASYNC)) == 0) {
		if (env->me_flags & MDB_WRITEMAP) {
			char* ptr = env->me_map + (offset & ~(env->me_os_psize - 1));
			int mode = (flags & MDB_MAPASYNC) ? MS_ASYNC : MS_SYNC;
			if (unlikely(msync(ptr, env->me_os_psize, mode) < 0)) {
				rc = errno;
				goto fail;
			}
		} else {
			while(unlikely(fdatasync(env->me_fd) < 0)) {
				rc = errno;
				if (rc != EINTR)
					goto undo;
			}
		}
	}

	/* LY: currently this can't happen, but... */
	if (unlikely(pending->mm_mapsize < prev_mapsize)) {
		mdb_assert(env, pending->mm_mapsize == env->me_mapsize);
		if (unlikely(mremap(env->me_map, prev_mapsize, pending->mm_mapsize,
						MREMAP_FIXED, pending->mm_address) == MAP_FAILED)) {
			rc = errno;
			goto fail;
		}
		if (unlikely(ftruncate(env->me_fd, pending->mm_mapsize) < 0)) {
			rc = errno;
			goto fail;
		}
	}

	return MDB_SUCCESS;

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

int __cold
mdb_env_create(MDB_env **env)
{
	MDB_env *e;

	e = calloc(1, sizeof(MDB_env));
	if (!e)
		return ENOMEM;

	e->me_maxreaders = DEFAULT_READERS;
	e->me_maxdbs = e->me_numdbs = CORE_DBS;
	e->me_fd = INVALID_HANDLE_VALUE;
	e->me_lfd = INVALID_HANDLE_VALUE;
	e->me_pid = getpid();
	GET_PAGESIZE(e->me_os_psize);
	VALGRIND_CREATE_MEMPOOL(e,0,0);
	e->me_signature = MDBX_ME_SIGNATURE;
	*env = e;
	return MDB_SUCCESS;
}

static int __cold
mdb_env_map(MDB_env *env, void *addr)
{
	unsigned flags = env->me_flags;

	int prot = PROT_READ;
	if (flags & MDB_WRITEMAP) {
		prot |= PROT_WRITE;
		if (ftruncate(env->me_fd, env->me_mapsize) < 0)
			return errno;
	}

	env->me_map = mmap(addr, env->me_mapsize, prot, MAP_SHARED, env->me_fd, 0);
	if (env->me_map == MAP_FAILED) {
		env->me_map = NULL;
		return errno;
	}

	/* Can happen because the address argument to mmap() is just a
	 * hint.  mmap() can pick another, e.g. if the range is in use.
	 * The MAP_FIXED flag would prevent that, but then mmap could
	 * instead unmap existing pages to make room for the new map.
	 */
	if (addr && env->me_map != addr) {
		errno = 0;	/* LY: clean errno as a hit for this case */
		return EBUSY;	/* TODO: Make a new MDB_* error code? */
	}

	if (madvise(env->me_map, env->me_mapsize, MADV_DONTFORK) < 0)
		return errno;

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

#ifdef MADV_DONTDUMP
	if (! (flags & MDB_PAGEPERTURB)) {
		(void) madvise(env->me_map, env->me_mapsize, MADV_DONTDUMP);
	}
#endif

	if (madvise(env->me_map, env->me_mapsize, MADV_WILLNEED) < 0)
		return errno;

	if (flags & MDB_NORDAHEAD) {
		/* Turn off readahead. It's harmful when the DB is larger than RAM. */
		if (madvise(env->me_map, env->me_mapsize, MADV_RANDOM) < 0)
			return errno;
	}

	/* Lock meta pages to avoid unexpected write,
	 *  before the data pages would be synchronized. */
	if ((flags & MDB_WRITEMAP) && mlock(env->me_map, env->me_psize * 2))
		return errno;

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

	return MDB_SUCCESS;
}

int __cold
mdb_env_set_mapsize(MDB_env *env, size_t size)
{
	if (unlikely(!env))
		return EINVAL;

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

	if (unlikely(size < env->me_psize * 8))
		return EINVAL;

	/* If env is already open, caller is responsible for making
	 * sure there are no active txns.
	 */
	if (env->me_map) {
		int rc;
		MDB_meta *meta;
		void *old;
		if (env->me_txn)
			return EINVAL;
		meta = mdb_meta_head_w(env);
		if (!size)
			size = meta->mm_mapsize;
		{
			/* Silently round up to minimum if the size is too small */
			size_t minsize = (meta->mm_last_pg + 1) * env->me_psize;
			if (size < minsize)
				size = minsize;
		}
		munmap(env->me_map, env->me_mapsize);
#ifdef USE_VALGRIND
		VALGRIND_DISCARD(env->me_valgrind_handle);
		env->me_valgrind_handle = -1;
#endif
		env->me_mapsize = size;
		old = (env->me_flags & MDB_FIXEDMAP) ? env->me_map : NULL;
		rc = mdb_env_map(env, old);
		if (rc)
			return rc;
	}
	env->me_mapsize = size;
	if (env->me_psize)
		env->me_maxpg = env->me_mapsize / env->me_psize;
	return MDB_SUCCESS;
}

int __cold
mdb_env_set_maxdbs(MDB_env *env, MDB_dbi dbs)
{
	if (unlikely(!env))
		return EINVAL;

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

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

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

int __cold
mdb_env_set_maxreaders(MDB_env *env, unsigned readers)
{
	if (unlikely(!env || readers < 1))
		return EINVAL;

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

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

	env->me_maxreaders = readers;
	return MDB_SUCCESS;
}

int __cold
mdb_env_get_maxreaders(MDB_env *env, unsigned *readers)
{
	if (!env || !readers)
		return EINVAL;

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

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

static int __cold
mdb_fsize(HANDLE fd, size_t *size)
{
	struct stat st;

	if (fstat(fd, &st))
		return errno;

	*size = st.st_size;
	return MDB_SUCCESS;
}

/** Further setup required for opening an LMDB environment
 */
static int __cold
mdb_env_open2(MDB_env *env, MDB_meta *meta)
{
	unsigned flags = env->me_flags;
	int i, newenv = 0, rc;

	if ((i = mdb_env_read_header(env, meta)) != 0) {
		if (i != ENOENT)
			return i;
		mdb_debug("new mdbenv");
		newenv = 1;
		env->me_psize = env->me_os_psize;
		if (env->me_psize > MAX_PAGESIZE)
			env->me_psize = MAX_PAGESIZE;
		memset(meta, 0, sizeof(*meta));
		mdb_env_init_meta0(env, meta);
		meta->mm_mapsize = DEFAULT_MAPSIZE;
	} else {
		env->me_psize = meta->mm_psize;
	}

	/* Was a mapsize configured? */
	if (!env->me_mapsize) {
		env->me_mapsize = meta->mm_mapsize;
	}
	{
		/* Make sure mapsize >= committed data size.  Even when using
		 * mm_mapsize, which could be broken in old files (ITS#7789).
		 */
		size_t minsize = (meta->mm_last_pg + 1) * meta->mm_psize;
		if (env->me_mapsize < minsize)
			env->me_mapsize = minsize;
	}
	meta->mm_mapsize = env->me_mapsize;

	if (newenv && !(flags & MDB_FIXEDMAP)) {
		/* mdb_env_map() may grow the datafile.  Write the metapages
		 * first, so the file will be valid if initialization fails.
		 * Except with FIXEDMAP, since we do not yet know mm_address.
		 * We could fill in mm_address later, but then a different
		 * program might end up doing that - one with a memory layout
		 * and map address which does not suit the main program.
		 */
		rc = mdb_env_init_meta(env, meta);
		if (rc)
			return rc;
		newenv = 0;
	}

	rc = mdb_env_map(env, (flags & MDB_FIXEDMAP) ? meta->mm_address : NULL);
	if (rc)
		return rc;

	if (newenv) {
		if (flags & MDB_FIXEDMAP)
			meta->mm_address = env->me_map;
		i = mdb_env_init_meta(env, meta);
		if (i != MDB_SUCCESS) {
			return i;
		}
	}

	env->me_maxfree_1pg = (env->me_psize - PAGEHDRSZ) / sizeof(pgno_t) - 1;
	env->me_nodemax = (((env->me_psize - PAGEHDRSZ) / MDB_MINKEYS) & -2)
		- sizeof(indx_t);
	env->me_maxkey_limit = env->me_nodemax - (NODESIZE + sizeof(MDB_db));
	env->me_maxpg = env->me_mapsize / env->me_psize;

	if (MDB_MAXKEYSIZE > env->me_maxkey_limit)
		return MDB_BAD_VALSIZE;

	return MDB_SUCCESS;
}

static pthread_mutex_t mdb_rthc_lock = PTHREAD_MUTEX_INITIALIZER;

/** Release a reader thread's slot in the reader lock table.
 *	This function is called automatically when a thread exits.
 * @param[in] ptr This points to the MDB_rthc of a slot in the reader lock table.
 */

/* LY: TODO: Yet another problem is here - segfault in case if a DSO will
 * be unloaded before a thread would been finished. */
static ATTRIBUTE_NO_SANITIZE_THREAD
void mdb_env_reader_destr(void *ptr)
{
	struct MDB_rthc* rthc = ptr;
	MDB_reader *reader;

	mdb_ensure(NULL, pthread_mutex_lock(&mdb_rthc_lock) == 0);
	reader = rthc->rc_reader;
	if (reader && reader->mr_pid == getpid()) {
		mdb_ensure(NULL, reader->mr_rthc == rthc);
		rthc->rc_reader = NULL;
		reader->mr_rthc = NULL;
		mdb_compiler_barrier();
		reader->mr_pid = 0;
		mdb_coherent_barrier();
	}
	mdb_ensure(NULL, pthread_mutex_unlock(&mdb_rthc_lock) == 0);
	free(rthc);
}

/** Downgrade the exclusive lock on the region back to shared */
static int __cold
mdb_env_share_locks(MDB_env *env, int *excl)
{
	struct flock lock_info;
	int rc = 0;

	/* The shared lock replaces the existing lock */
	memset((void *)&lock_info, 0, sizeof(lock_info));
	lock_info.l_type = F_RDLCK;
	lock_info.l_whence = SEEK_SET;
	lock_info.l_start = 0;
	lock_info.l_len = 1;
	while ((rc = fcntl(env->me_lfd, F_SETLK, &lock_info)) &&
			(rc = errno) == EINTR) ;
	*excl = rc ? -1 : 0;	/* error may mean we lost the lock */

	return rc;
}

/** Try to get exclusive lock, otherwise shared.
 *	Maintain *excl = -1: no/unknown lock, 0: shared, 1: exclusive.
 */
static int __cold
mdb_env_excl_lock(MDB_env *env, int *excl)
{
	int rc = 0;
	struct flock lock_info;

	memset((void *)&lock_info, 0, sizeof(lock_info));
	lock_info.l_type = F_WRLCK;
	lock_info.l_whence = SEEK_SET;
	lock_info.l_start = 0;
	lock_info.l_len = 1;
	while ((rc = fcntl(env->me_lfd, F_SETLK, &lock_info)) &&
			(rc = errno) == EINTR) ;
	if (!rc) {
		*excl = 1;
	} else {
		lock_info.l_type = F_RDLCK;
		while ((rc = fcntl(env->me_lfd, F_SETLKW, &lock_info)) &&
				(rc = errno) == EINTR) ;
		if (rc == 0)
			*excl = 0;
	}
	return rc;
}

#ifdef MDB_USE_HASH
/*
 * hash_64 - 64 bit Fowler/Noll/Vo-0 FNV-1a hash code
 *
 * @(#) $Revision: 5.1 $
 * @(#) $Id: hash_64a.c,v 5.1 2009/06/30 09:01:38 chongo Exp $
 * @(#) $Source: /usr/local/src/cmd/fnv/RCS/hash_64a.c,v $
 *
 *	  http://www.isthe.com/chongo/tech/comp/fnv/index.html
 *
 ***
 *
 * Please do not copyright this code.  This code is in the public domain.
 *
 * LANDON CURT NOLL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO
 * EVENT SHALL LANDON CURT NOLL BE LIABLE FOR ANY SPECIAL, 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.
 *
 * By:
 *	chongo <Landon Curt Noll> /\oo/\
 *	  http://www.isthe.com/chongo/
 *
 * Share and Enjoy!	:-)
 */

typedef unsigned long long	mdb_hash_t;
#define MDB_HASH_INIT ((mdb_hash_t)0xcbf29ce484222325ULL)

/** perform a 64 bit Fowler/Noll/Vo FNV-1a hash on a buffer
 * @param[in] val	value to hash
 * @param[in] hval	initial value for hash
 * @return 64 bit hash
 *
 * NOTE: To use the recommended 64 bit FNV-1a hash, use MDB_HASH_INIT as the
 * 	 hval arg on the first call.
 */
static mdb_hash_t
mdb_hash_val(MDB_val *val, mdb_hash_t hval)
{
	unsigned char *s = (unsigned char *)val->mv_data;	/* unsigned string */
	unsigned char *end = s + val->mv_size;
	/*
	 * FNV-1a hash each octet of the string
	 */
	while (s < end) {
		/* xor the bottom with the current octet */
		hval ^= (mdb_hash_t)*s++;

		/* multiply by the 64 bit FNV magic prime mod 2^64 */
		hval += (hval << 1) + (hval << 4) + (hval << 5) +
			(hval << 7) + (hval << 8) + (hval << 40);
	}
	/* return our new hash value */
	return hval;
}

/** Hash the string and output the encoded hash.
 * This uses modified RFC1924 Ascii85 encoding to accommodate systems with
 * very short name limits. We don't care about the encoding being reversible,
 * we just want to preserve as many bits of the input as possible in a
 * small printable string.
 * @param[in] str string to hash
 * @param[out] encbuf an array of 11 chars to hold the hash
 */
static const char mdb_a85[]= "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~";

static void __cold
mdb_pack85(unsigned long l, char *out)
{
	int i;

	for (i=0; i<5; i++) {
		*out++ = mdb_a85[l % 85];
		l /= 85;
	}
}

static void __cold
mdb_hash_enc(MDB_val *val, char *encbuf)
{
	mdb_hash_t h = mdb_hash_val(val, MDB_HASH_INIT);

	mdb_pack85(h, encbuf);
	mdb_pack85(h>>32, encbuf+5);
	encbuf[10] = '\0';
}
#endif

/** Open and/or initialize the lock region for the environment.
 * @param[in] env The LMDB environment.
 * @param[in] lpath The pathname of the file used for the lock region.
 * @param[in] mode The Unix permissions for the file, if we create it.
 * @param[in,out] excl In -1, out lock type: -1 none, 0 shared, 1 exclusive
 * @return 0 on success, non-zero on failure.
 */
static int __cold
mdb_env_setup_locks(MDB_env *env, char *lpath, int mode, int *excl)
{
	int fdflags;
	int rc;
	off_t size, rsize;
	void *m;

	env->me_lfd = open(lpath, O_RDWR|O_CREAT|O_CLOEXEC, mode);
	if (env->me_lfd == INVALID_HANDLE_VALUE) {
		rc = errno;
		if (rc == EROFS && (env->me_flags & MDB_RDONLY)) {
			return MDB_SUCCESS;
		}
		return rc;
	}

	/* Lose record locks when exec*() */
	if ((fdflags = fcntl(env->me_lfd, F_GETFD) | FD_CLOEXEC) >= 0)
			fcntl(env->me_lfd, F_SETFD, fdflags);

	if (!(env->me_flags & MDB_NOTLS)) {
		rc = pthread_key_create(&env->me_txkey, mdb_env_reader_destr);
		if (rc)
			return rc;
		env->me_flags |= MDB_ENV_TXKEY;
	}

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

	size = lseek(env->me_lfd, 0, SEEK_END);
	if (size == -1) return errno;
	rsize = (env->me_maxreaders-1) * sizeof(MDB_reader) + sizeof(MDB_txninfo);
	if (size < rsize && *excl > 0) {
		if (ftruncate(env->me_lfd, rsize) != 0) return errno;
	} else {
		rsize = size;
		size = rsize - sizeof(MDB_txninfo);
		env->me_maxreaders = size/sizeof(MDB_reader) + 1;
	}

	m = mmap(NULL, rsize, PROT_READ|PROT_WRITE, MAP_SHARED, env->me_lfd, 0);
	if (m == MAP_FAILED)
		return errno;
	env->me_txns = m;

#ifdef MADV_NOHUGEPAGE
	(void) madvise(env->me_txns, rsize, MADV_NOHUGEPAGE);
#endif

#ifdef MADV_DODUMP
	(void) madvise(env->me_txns, rsize, MADV_DODUMP);
#endif

	if (madvise(env->me_txns, rsize, MADV_DONTFORK) < 0)
		return errno;

	if (madvise(env->me_txns, rsize, MADV_WILLNEED) < 0)
		return errno;

	if (madvise(env->me_txns, rsize, MADV_RANDOM) < 0)
		return errno;

	if (*excl > 0) {
		pthread_mutexattr_t mattr;

		if ((rc = pthread_mutexattr_init(&mattr))
			|| (rc = pthread_mutexattr_setpshared(&mattr, PTHREAD_PROCESS_SHARED))
#if MDB_USE_ROBUST
			|| (rc = pthread_mutexattr_setrobust(&mattr, PTHREAD_MUTEX_ROBUST))
#endif /* MDB_USE_ROBUST */
			|| (rc = pthread_mutex_init(&env->me_txns->mti_rmutex, &mattr))
			|| (rc = pthread_mutex_init(&env->me_txns->mti_wmutex, &mattr)))
			return rc;
		pthread_mutexattr_destroy(&mattr);

		env->me_txns->mti_magic = MDB_MAGIC;
		env->me_txns->mti_format = MDB_LOCK_FORMAT;
		env->me_txns->mti_txnid = ~0L;
		env->me_txns->mti_numreaders = 0;
	} else {
		if (env->me_txns->mti_magic != MDB_MAGIC) {
			mdb_debug("lock region has invalid magic");
			return MDB_INVALID;
		}
		if (env->me_txns->mti_format != MDB_LOCK_FORMAT) {
			mdb_debug("lock region has format+version 0x%x, expected 0x%x",
				env->me_txns->mti_format, MDB_LOCK_FORMAT);
			return MDB_VERSION_MISMATCH;
		}
	}

	return MDB_SUCCESS;
}

	/** The name of the lock file in the DB environment */
#define LOCKNAME	"/lock.mdb"
	/** The name of the data file in the DB environment */
#define DATANAME	"/data.mdb"
	/** The suffix of the lock file when no subdir is used */
#define LOCKSUFF	"-lock"
	/** Only a subset of the @ref mdb_env flags can be changed
	 *	at runtime. Changing other flags requires closing the
	 *	environment and re-opening it with the new flags.
	 */
#define	CHANGEABLE	(MDB_NOSYNC|MDB_NOMETASYNC|MDB_MAPASYNC| \
	MDB_NOMEMINIT|MDB_COALESCE|MDB_PAGEPERTURB)
#define	CHANGELESS	(MDB_FIXEDMAP|MDB_NOSUBDIR|MDB_RDONLY| \
	MDB_WRITEMAP|MDB_NOTLS|MDB_NORDAHEAD|MDB_LIFORECLAIM)

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

#if ! MDBX_MODE_ENABLED
static
#endif /* ! MDBX_MODE_ENABLED */
int __cold
mdbx_env_open_ex(MDB_env *env, const char *path, unsigned flags, mode_t mode, int *exclusive)
{
	int		oflags, rc, len, excl = -1;
	char *lpath, *dpath;

	if (unlikely(!env || !path))
		return EINVAL;

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

#if MDB_LIFORECLAIM
	/* LY: don't allow LIFO with just NOMETASYNC */
	if ((flags & (MDB_NOMETASYNC | MDB_LIFORECLAIM | MDB_NOSYNC))
			== (MDB_NOMETASYNC | MDB_LIFORECLAIM))
		return EINVAL;
#endif /* MDB_LIFORECLAIM */

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

	len = strlen(path);
	if (flags & MDB_NOSUBDIR) {
		rc = len + sizeof(LOCKSUFF) + len + 1;
	} else {
		rc = len + sizeof(LOCKNAME) + len + sizeof(DATANAME);
	}
	lpath = malloc(rc);
	if (!lpath)
		return ENOMEM;
	if (flags & MDB_NOSUBDIR) {
		dpath = lpath + len + sizeof(LOCKSUFF);
		sprintf(lpath, "%s" LOCKSUFF, path);
		strcpy(dpath, path);
	} else {
		dpath = lpath + len + sizeof(LOCKNAME);
		sprintf(lpath, "%s" LOCKNAME, path);
		sprintf(dpath, "%s" DATANAME, path);
	}

	rc = MDB_SUCCESS;
	flags |= env->me_flags;
	if (flags & MDB_RDONLY) {
		/* LY: silently ignore irrelevant flags when we're only getting read access */
		flags &= ~(MDB_WRITEMAP | MDB_MAPASYNC | MDB_NOSYNC | MDB_NOMETASYNC
			| MDB_COALESCE | MDB_LIFORECLAIM | MDB_NOMEMINIT);
	} else {
		if (!((env->me_free_pgs = mdb_midl_alloc(MDB_IDL_UM_MAX))
				&& (env->me_dirty_list = calloc(MDB_IDL_UM_SIZE, sizeof(MDB_ID2)))))
			rc = ENOMEM;
	}
	env->me_flags = flags |= MDB_ENV_ACTIVE;
	if (rc)
		goto leave;

	env->me_path = strdup(path);
	env->me_dbxs = calloc(env->me_maxdbs, sizeof(MDB_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 = ENOMEM;
		goto leave;
	}
	env->me_dbxs[FREE_DBI].md_cmp = mdb_cmp_int_ai; /* aligned MDB_INTEGERKEY */

	/* For RDONLY, get lockfile after we know datafile exists */
	if (!(flags & MDB_RDONLY)) {
		rc = mdb_env_setup_locks(env, lpath, mode, &excl);
		if (rc)
			goto leave;
	}

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

	env->me_fd = open(dpath, oflags, mode);
	if (env->me_fd == INVALID_HANDLE_VALUE) {
		rc = errno;
		goto leave;
	}

	if (flags & MDB_RDONLY) {
		rc = mdb_env_setup_locks(env, lpath, mode, &excl);
		if (rc)
			goto leave;
	}

	MDB_meta meta;
	if ((rc = mdb_env_open2(env, &meta)) == MDB_SUCCESS) {
		mdb_debug("opened dbenv %p", (void *) env);
		if (excl > 0) {
			env->me_txns->mti_txnid = meta.mm_txnid;
			if (exclusive == NULL || *exclusive < 2) {
				/* LY: downgrade lock only if exclusive access not requested.
				 *     in case exclusive==1, just leave value as is. */
				rc = mdb_env_share_locks(env, &excl);
				if (rc)
					goto leave;
			}
		} else if (exclusive) {
			/* LY: just indicate that is not an exclusive access. */
			*exclusive = 0;
		}
		if (!(flags & MDB_RDONLY)) {
			MDB_txn *txn;
			int tsize = sizeof(MDB_txn), size = tsize + env->me_maxdbs *
				(sizeof(MDB_db)+sizeof(MDB_cursor *)+sizeof(unsigned)+1);
			if ((env->me_pbuf = calloc(1, env->me_psize)) &&
				(txn = calloc(1, size)))
			{
				txn->mt_dbs = (MDB_db *)((char *)txn + tsize);
				txn->mt_cursors = (MDB_cursor **)(txn->mt_dbs + env->me_maxdbs);
				txn->mt_dbiseqs = (unsigned *)(txn->mt_cursors + env->me_maxdbs);
				txn->mt_dbflags = (unsigned char *)(txn->mt_dbiseqs + env->me_maxdbs);
				txn->mt_env = env;
				txn->mt_dbxs = env->me_dbxs;
				txn->mt_flags = MDB_TXN_FINISHED;
				env->me_txn0 = txn;
			} else {
				rc = ENOMEM;
			}
		}
	}

#if MDB_DEBUG
	if (rc == MDB_SUCCESS) {
		MDB_meta *meta = mdb_meta_head_r(env);
		MDB_db *db = &meta->mm_dbs[MAIN_DBI];
		int toggle = ((char*) meta == PAGEDATA(env->me_map)) ? 0 : 1;

		mdb_debug("opened database version %u, pagesize %u",
			meta->mm_version, env->me_psize);
		mdb_debug("using meta page %d, txn %zu", toggle, meta->mm_txnid);
		mdb_debug("depth: %u",             db->md_depth);
		mdb_debug("entries: %zu",        db->md_entries);
		mdb_debug("branch pages: %zu",   db->md_branch_pages);
		mdb_debug("leaf pages: %zu",     db->md_leaf_pages);
		mdb_debug("overflow pages: %zu", db->md_overflow_pages);
		mdb_debug("root: %zu",           db->md_root);
	}
#endif

leave:
	if (rc)
		mdb_env_close0(env);
	free(lpath);
	return rc;
}

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

/** Destroy resources from mdb_env_open(), clear our readers & DBIs */
static void __cold
mdb_env_close0(MDB_env *env)
{
	int i;

	if (!(env->me_flags & MDB_ENV_ACTIVE))
		return;

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

	free(env->me_pbuf);
	free(env->me_dbiseqs);
	free(env->me_dbflags);
	free(env->me_path);
	free(env->me_dirty_list);
	if (env->me_txn0)
		mdb_midl_free(env->me_txn0->mt_lifo_reclaimed);
	free(env->me_txn0);
	mdb_midl_free(env->me_free_pgs);

	if (env->me_flags & MDB_ENV_TXKEY) {
		pthread_key_delete(env->me_txkey);
	}

	if (env->me_map) {
		munmap(env->me_map, env->me_mapsize);
#ifdef USE_VALGRIND
		VALGRIND_DISCARD(env->me_valgrind_handle);
		env->me_valgrind_handle = -1;
#endif
	}
	if (env->me_fd != INVALID_HANDLE_VALUE)
		(void) close(env->me_fd);

	pid_t pid = env->me_pid;
	/* Clearing readers is done in this function because
	 * me_txkey with its destructor must be disabled first.
	 *
	 * We skip the the reader mutex, so we touch only
	 * data owned by this process (me_close_readers and
	 * our readers), and clear each reader atomically.
	 */
	if (pid == getpid()) {
		mdb_ensure(env, pthread_mutex_lock(&mdb_rthc_lock) == 0);
		for (i = env->me_close_readers; --i >= 0; ) {
			MDB_reader *reader = &env->me_txns->mti_readers[i];
			if (reader->mr_pid == pid) {
				struct MDB_rthc *rthc = reader->mr_rthc;
				if (rthc) {
					mdb_ensure(env, rthc->rc_reader == reader);
					rthc->rc_reader = NULL;
					reader->mr_rthc = NULL;
				}
				reader->mr_pid = 0;
			}
		}
		mdb_coherent_barrier();
		mdb_ensure(env, pthread_mutex_unlock(&mdb_rthc_lock) == 0);
	}

	munmap((void *)env->me_txns, (env->me_maxreaders-1)*sizeof(MDB_reader)+sizeof(MDB_txninfo));
	env->me_txns = NULL;

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

	env->me_flags &= ~(MDB_ENV_ACTIVE|MDB_ENV_TXKEY);
}

#if ! MDBX_MODE_ENABLED
static
#endif /* ! MDBX_MODE_ENABLED */
int __cold
mdbx_env_close_ex(MDB_env *env, int dont_sync)
{
	MDB_page *dp;
	int rc = MDB_SUCCESS;

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

	if (! dont_sync && env->me_txns)
		rc = mdb_env_sync(env, 1);

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

	mdb_env_close0(env);
	env->me_signature = 0;
	free(env);

	return rc;
}

void __cold
mdb_env_close(MDB_env *env)
{
	mdbx_env_close_ex(env, 0);
}

/* LY: fast enough on most arches
 *
 *                /
 *                | -1, a < b
 * cmp2int(a,b) = <  0, a == b
 *                |  1, a > b
 *                \
 */
#if 1
#	define mdbx_cmp2int(a, b) (((b) > (a)) ? -1 : (a) > (b))
#else
#	define mdbx_cmp2int(a, b) (((a) > (b)) - ((b) > (a)))
#endif

/** Compare two items pointing at aligned unsigned int's. */
static int __hot
mdb_cmp_int_ai(const MDB_val *a, const MDB_val *b)
{
	mdb_assert(NULL, a->mv_size == b->mv_size);
	mdb_assert(NULL, 0 == (uintptr_t) a->mv_data % sizeof(int)
				&& 0 == (uintptr_t) b->mv_data % sizeof(int));

	if (sizeof(int) != sizeof(size_t) && likely(a->mv_size == sizeof(size_t)))
		return mdbx_cmp2int( *(size_t *)a->mv_data, *(size_t *)b->mv_data );

	mdb_assert(NULL, a->mv_size == sizeof(int) );
	return mdbx_cmp2int( *(unsigned *)a->mv_data, *(unsigned *)b->mv_data );
}

/** Compare two items pointing at 2-byte aligned unsigned int's. */
static int __hot
mdb_cmp_int_a2(const MDB_val *a, const MDB_val *b)
{
	mdb_assert(NULL, a->mv_size == b->mv_size);
	mdb_assert(NULL, 0 == (uintptr_t) a->mv_data % sizeof(uint16_t)
				&& 0 == (uintptr_t) b->mv_data % sizeof(uint16_t));
#ifdef MISALIGNED_OK
	if (sizeof(int) != sizeof(size_t) && likely(a->mv_size == sizeof(size_t)))
		return mdbx_cmp2int( *(size_t *)a->mv_data, *(size_t *)b->mv_data );

	mdb_assert(NULL, a->mv_size == sizeof(int) );
	return mdbx_cmp2int( *(unsigned *)a->mv_data, *(unsigned *)b->mv_data );
#else
	mdb_assert(NULL, 0 == a->mv_size % sizeof(uint16_t));
	{
		int diff;
		const uint16_t *pa, *pb, *end;

#if BYTE_ORDER == LITTLE_ENDIAN
		end = (const uint16_t *) a->mv_data;
		pa = (const uint16_t *) ((char *) a->mv_data + a->mv_size);
		pb = (const uint16_t *) ((char *) b->mv_data + a->mv_size);
		do {
			diff = *--pa - *--pb;
#else /* BYTE_ORDER */
		end = (const uint16_t *) ((char *) a->mv_data + a->mv_size);
		pa = (const uint16_t *) a->mv_data;
		pb = (const uint16_t *) b->mv_data;
		do {
			diff = *pa++ - *pb++;
#endif /* BYTE_ORDER */
			if (likely(diff != 0)) break;
		} while(pa != end);
		return diff;
	}
#endif /* MISALIGNED_OK */
}

/** Compare two items pointing at unsigneds of unknown alignment.
 *
 *	This is also set as #MDB_INTEGERDUP|#MDB_DUPFIXED's #MDB_dbx.%md_dcmp.
 */
static int __hot
mdb_cmp_int_ua(const MDB_val *a, const MDB_val *b)
{
	mdb_assert(NULL, a->mv_size == b->mv_size);
#if MISALIGNED_OK
	if (sizeof(int) != sizeof(size_t) && likely(a->mv_size == sizeof(size_t)))
		return mdbx_cmp2int( *(size_t *)a->mv_data, *(size_t *)b->mv_data );

	mdb_assert(NULL, a->mv_size == sizeof(int) );
	return mdbx_cmp2int( *(unsigned *)a->mv_data, *(unsigned *)b->mv_data );
#else
	mdb_assert(NULL, a->mv_size == sizeof(int) || a->mv_size == sizeof(size_t));
#if BYTE_ORDER == LITTLE_ENDIAN
	{
		int diff;
		const uint8_t *pa, *pb;

		pa = (const uint8_t *)a->mv_data + a->mv_size;
		pb = (const uint8_t *)b->mv_data + a->mv_size;

		do {
			diff = *--pa - *--pb;
			if (likely(diff)) break;
		} while(pa != a->mv_data);
		return diff;
	}
#else /* BYTE_ORDER */
	return memcmp(a->mv_data, b->mv_data, a->mv_size);
#endif /* BYTE_ORDER */
#endif /* MISALIGNED_OK */
}

/** Compare two items lexically */
static int __hot
mdb_cmp_memn(const MDB_val *a, const MDB_val *b)
{
	size_t minlen = (a->mv_size < b->mv_size) ? a->mv_size : b->mv_size;
	int diff = memcmp(a->mv_data, b->mv_data, minlen);
	return likely(diff) ? diff : mdbx_cmp2int(a->mv_size, b->mv_size);
}

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

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

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

/** 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 MDB_node * __hot
mdb_node_search(MDB_cursor *mc, MDB_val *key, int *exactp)
{
	unsigned	 i = 0, nkeys;
	int		 low, high;
	int		 rc = 0;
	MDB_page *mp = mc->mc_pg[mc->mc_top];
	MDB_node	*node = NULL;
	MDB_val	 nodekey;
	MDB_cmp_func *cmp;
	DKBUF;

	nkeys = NUMKEYS(mp);

	mdb_debug("searching %u keys in %s %spage %zu",
		nkeys, IS_LEAF(mp) ? "leaf" : "branch", IS_SUBP(mp) ? "sub-" : "",
		mdb_dbg_pgno(mp));

	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 mdb_cmp_int_ai.
	 */
	if (cmp == mdb_cmp_int_a2 && IS_BRANCH(mp))
		cmp = mdb_cmp_int_ai;

	if (IS_LEAF2(mp)) {
		nodekey.mv_size = mc->mc_db->md_xsize;
		node = NODEPTR(mp, 0);	/* fake */
		while (low <= high) {
			i = (low + high) >> 1;
			nodekey.mv_data = LEAF2KEY(mp, i, nodekey.mv_size);
			rc = cmp(key, &nodekey);
			mdb_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.mv_size = NODEKSZ(node);
			nodekey.mv_data = NODEKEY(node);

			rc = cmp(key, &nodekey);
			if (IS_LEAF(mp))
				mdb_debug("found leaf index %u [%s], rc = %i",
					i, DKEY(&nodekey), rc);
			else
				mdb_debug("found branch index %u [%s -> %zu], 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 (!IS_LEAF2(mp))
			node = NODEPTR(mp, i);
	}
	if (exactp)
		*exactp = (rc == 0 && nkeys > 0);
	/* store the key index */
	mc->mc_ki[mc->mc_top] = i;
	if (i >= nkeys)
		/* There is no entry larger or equal to the key. */
		return NULL;

	/* nodeptr is fake for LEAF2 */
	return node;
}

#if 0
static void
mdb_cursor_adjust(MDB_cursor *mc, func)
{
	MDB_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
mdb_cursor_pop(MDB_cursor *mc)
{
	if (mc->mc_snum) {
		mdb_debug("popped page %zu 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. */
static int
mdb_cursor_push(MDB_cursor *mc, MDB_page *mp)
{
	mdb_debug("pushing page %zu on db %d cursor %p", mp->mp_pgno,
		DDBI(mc), (void *) mc);

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

	mc->mc_top = mc->mc_snum++;
	mc->mc_pg[mc->mc_top] = mp;
	mc->mc_ki[mc->mc_top] = 0;

	return MDB_SUCCESS;
}

/** Find the address of the page corresponding to a given page number.
 * @param[in] txn the transaction for this access.
 * @param[in] pgno the page number for the page to retrieve.
 * @param[out] ret address of a pointer where the page's address will be stored.
 * @param[out] lvl dirty_list inheritance level of found page. 1=current txn, 0=mapped page.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_get(MDB_txn *txn, pgno_t pgno, MDB_page **ret, int *lvl)
{
	MDB_env *env = txn->mt_env;
	MDB_page *p = NULL;
	int level;

	if (! (txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_WRITEMAP))) {
		MDB_txn *tx2 = txn;
		level = 1;
		do {
			MDB_ID2L dl = tx2->mt_u.dirty_list;
			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_pgs) {
				MDB_ID pn = pgno << 1;
				x = mdb_midl_search(tx2->mt_spill_pgs, pn);
				if (x <= tx2->mt_spill_pgs[0] && tx2->mt_spill_pgs[x] == pn) {
					p = (MDB_page *)(env->me_map + env->me_psize * pgno);
					goto done;
				}
			}
			if (dl[0].mid) {
				unsigned x = mdb_mid2l_search(dl, pgno);
				if (x <= dl[0].mid && dl[x].mid == pgno) {
					p = dl[x].mptr;
					goto done;
				}
			}
			level++;
		} while ((tx2 = tx2->mt_parent) != NULL);
	}

	if (likely(pgno < txn->mt_next_pgno)) {
		level = 0;
		p = (MDB_page *)(env->me_map + env->me_psize * pgno);
	} else {
		mdb_debug("page %zu not found", pgno);
		txn->mt_flags |= MDB_TXN_ERROR;
		return MDB_PAGE_NOTFOUND;
	}

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

/** Finish #mdb_page_search() / #mdb_page_search_lowest().
 *	The cursor is at the root page, set up the rest of it.
 */
static int
mdb_page_search_root(MDB_cursor *mc, MDB_val *key, int flags)
{
	MDB_page	*mp = mc->mc_pg[mc->mc_top];
	int rc;
	DKBUF;

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

		mdb_debug("branch page %zu 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
		 */
		mdb_cassert(mc, !mc->mc_dbi || NUMKEYS(mp) > 1);
		mdb_debug("found index 0 to page %zu", NODEPGNO(NODEPTR(mp, 0)));

		if (flags & (MDB_PS_FIRST|MDB_PS_LAST)) {
			i = 0;
			if (flags & MDB_PS_LAST)
				i = NUMKEYS(mp) - 1;
		} else {
			int	 exact;
			node = mdb_node_search(mc, key, &exact);
			if (node == NULL)
				i = NUMKEYS(mp) - 1;
			else {
				i = mc->mc_ki[mc->mc_top];
				if (!exact) {
					mdb_cassert(mc, i > 0);
					i--;
				}
			}
			mdb_debug("following index %u for key [%s]", i, DKEY(key));
		}

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

		if (unlikely((rc = mdb_page_get(mc->mc_txn, NODEPGNO(node), &mp, NULL)) != 0))
			return rc;

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

		if (flags & MDB_PS_MODIFY) {
			if (unlikely((rc = mdb_page_touch(mc)) != 0))
				return rc;
			mp = mc->mc_pg[mc->mc_top];
		}
	}

	if (unlikely(!IS_LEAF(mp))) {
		mdb_debug("internal error, index points to a %02X page!?",
			mp->mp_flags);
		mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
		return MDB_CORRUPTED;
	}

	mdb_debug("found leaf page %zu for key [%s]", mp->mp_pgno,
		key ? DKEY(key) : "null");
	mc->mc_flags |= C_INITIALIZED;
	mc->mc_flags &= ~C_EOF;

	return MDB_SUCCESS;
}

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

	if (unlikely((rc = mdb_page_get(mc->mc_txn, NODEPGNO(node), &mp, NULL)) != 0))
		return rc;

	mc->mc_ki[mc->mc_top] = 0;
	if (unlikely(rc = mdb_cursor_push(mc, mp)))
		return rc;
	return mdb_page_search_root(mc, NULL, MDB_PS_FIRST);
}

/** Search for the page a given key should be in.
 * Push it and its parent pages on the cursor stack.
 * @param[in,out] mc the cursor for this operation.
 * @param[in] key the key to search for, or NULL for first/last page.
 * @param[in] flags If MDB_PS_MODIFY is set, visited pages in the DB
 *   are touched (updated with new page numbers).
 *   If MDB_PS_FIRST or MDB_PS_LAST is set, find first or last leaf.
 *   This is used by #mdb_cursor_first() and #mdb_cursor_last().
 *   If MDB_PS_ROOTONLY set, just fetch root node, no further lookups.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_search(MDB_cursor *mc, MDB_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 & MDB_TXN_BLOCKED)) {
		mdb_debug("transaction has failed, must abort");
		return MDB_BAD_TXN;
	} else {
		/* Make sure we're using an up-to-date root */
		if (*mc->mc_dbflag & DB_STALE) {
				MDB_cursor mc2;
				if (unlikely(TXN_DBI_CHANGED(mc->mc_txn, mc->mc_dbi)))
					return MDB_BAD_DBI;
				mdb_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, NULL);
				rc = mdb_page_search(&mc2, &mc->mc_dbx->md_name, 0);
				if (rc)
					return rc;
				{
					MDB_val data;
					int exact = 0;
					uint16_t flags;
					MDB_node *leaf = mdb_node_search(&mc2,
						&mc->mc_dbx->md_name, &exact);
					if (!exact)
						return MDB_NOTFOUND;
					if (unlikely((leaf->mn_flags & (F_DUPDATA|F_SUBDATA)) != F_SUBDATA))
						return MDB_INCOMPATIBLE; /* not a named DB */
					rc = mdb_node_read(mc->mc_txn, leaf, &data);
					if (rc)
						return rc;
					memcpy(&flags, ((char *) data.mv_data + offsetof(MDB_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) != flags))
						return MDB_INCOMPATIBLE;
					memcpy(mc->mc_db, data.mv_data, sizeof(MDB_db));
				}
				*mc->mc_dbflag &= ~DB_STALE;
		}
		root = mc->mc_db->md_root;

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

	mdb_cassert(mc, root > 1);
	if (!mc->mc_pg[0] || mc->mc_pg[0]->mp_pgno != root)
		if (unlikely((rc = mdb_page_get(mc->mc_txn, root, &mc->mc_pg[0], NULL)) != 0))
			return rc;

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

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

	if (flags & MDB_PS_MODIFY) {
		if (unlikely(rc = mdb_page_touch(mc)))
			return rc;
	}

	if (flags & MDB_PS_ROOTONLY)
		return MDB_SUCCESS;

	return mdb_page_search_root(mc, key, flags);
}

static int
mdb_ovpage_free(MDB_cursor *mc, MDB_page *mp)
{
	MDB_txn *txn = mc->mc_txn;
	pgno_t pg = mp->mp_pgno;
	unsigned x = 0, ovpages = mp->mp_pages;
	MDB_env *env = txn->mt_env;
	MDB_IDL sl = txn->mt_spill_pgs;
	MDB_ID pn = pg << 1;
	int rc;

	mdb_debug("free ov page %zu (%d)", 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_pghead: me_pglast 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_pghead &&
		!txn->mt_parent &&
		((mp->mp_flags & P_DIRTY) ||
		 (sl && (x = mdb_midl_search(sl, pn)) <= sl[0] && sl[x] == pn)))
	{
		unsigned i, j;
		pgno_t *mop;
		MDB_ID2 *dl, ix, iy;
		rc = mdb_midl_need(&env->me_pghead, 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_u.dirty_list;
		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 {
				mdb_cassert(mc, x > 1);
				j = ++(dl[0].mid);
				dl[j] = ix;		/* Unsorted. OK when MDB_TXN_ERROR. */
				txn->mt_flags |= MDB_TXN_ERROR;
				return MDB_CORRUPTED;
			}
		}
		txn->mt_dirty_room++;
		if (!(env->me_flags & MDB_WRITEMAP))
			mdb_dpage_free(env, mp);
release:
		/* Insert in me_pghead */
		mop = env->me_pghead;
		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 = mdb_midl_append_range(&txn->mt_free_pgs, pg, ovpages);
		if (unlikely(rc))
			return rc;
	}
	mc->mc_db->md_overflow_pages -= ovpages;
	return 0;
}

/** Return the data associated with a given node.
 * @param[in] txn The transaction for this operation.
 * @param[in] leaf The node being read.
 * @param[out] data Updated to point to the node's data.
 * @return 0 on success, non-zero on failure.
 */
static MDB_INLINE int
mdb_node_read(MDB_txn *txn, MDB_node *leaf, MDB_val *data)
{
	MDB_page	*omp;		/* overflow page */
	pgno_t		 pgno;
	int rc;

	if (!F_ISSET(leaf->mn_flags, F_BIGDATA)) {
		data->mv_size = NODEDSZ(leaf);
		data->mv_data = NODEDATA(leaf);
		return MDB_SUCCESS;
	}

	/* Read overflow data.
	 */
	data->mv_size = NODEDSZ(leaf);
	memcpy(&pgno, NODEDATA(leaf), sizeof(pgno));
	if (unlikely((rc = mdb_page_get(txn, pgno, &omp, NULL)) != 0)) {
		mdb_debug("read overflow page %zu failed", pgno);
		return rc;
	}
	data->mv_data = PAGEDATA(omp);

	return MDB_SUCCESS;
}

int
mdb_get(MDB_txn *txn, MDB_dbi dbi,
	MDB_val *key, MDB_val *data)
{
	MDB_cursor	mc;
	MDB_xcursor	mx;
	int exact = 0;
	DKBUF;

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

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

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

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

	if (unlikely(txn->mt_flags & MDB_TXN_BLOCKED))
		return MDB_BAD_TXN;

	mdb_cursor_init(&mc, txn, dbi, &mx);
	return mdb_cursor_set(&mc, key, data, MDB_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.
 * @param[in] mc The cursor for this operation.
 * @param[in] move_right Non-zero if the right sibling is requested,
 * otherwise the left sibling.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_cursor_sibling(MDB_cursor *mc, int move_right)
{
	int		 rc;
	MDB_node	*indx;
	MDB_page	*mp;

	if (unlikely(mc->mc_snum < 2)) {
		return MDB_NOTFOUND;		/* root has no siblings */
	}

	mdb_cursor_pop(mc);
	mdb_debug("parent page is page %zu, 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)) {
		mdb_debug("no more keys left, moving to %s sibling",
			move_right ? "right" : "left");
		if (unlikely((rc = mdb_cursor_sibling(mc, move_right)) != MDB_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]--;
		mdb_debug("just moving to %s index key %u",
			move_right ? "right" : "left", mc->mc_ki[mc->mc_top]);
	}
	mdb_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 = mdb_page_get(mc->mc_txn, 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;
	}

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

	return MDB_SUCCESS;
}

/** Move the cursor to the next data item. */
static int
mdb_cursor_next(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op)
{
	MDB_page	*mp;
	MDB_node	*leaf;
	int rc;

	if (unlikely(mc->mc_flags & C_EOF)) {
		return MDB_NOTFOUND;
	}
	if (!(mc->mc_flags & C_INITIALIZED))
		return mdb_cursor_first(mc, key, data);

	mp = mc->mc_pg[mc->mc_top];

	if (mc->mc_db->md_flags & MDB_DUPSORT) {
		leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
		if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
			if (op == MDB_NEXT || op == MDB_NEXT_DUP) {
				rc = mdb_cursor_next(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_NEXT);
				if (op != MDB_NEXT || rc != MDB_NOTFOUND) {
					if (likely(rc == MDB_SUCCESS))
						MDB_GET_KEY(leaf, key);
					return rc;
				}
			}
		} else {
			mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);
			if (op == MDB_NEXT_DUP)
				return MDB_NOTFOUND;
		}
	}

	mdb_debug("cursor_next: top page is %zu in cursor %p",
		mdb_dbg_pgno(mp), (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)) {
		mdb_debug("=====> move to next sibling page");
		if (unlikely((rc = mdb_cursor_sibling(mc, 1)) != MDB_SUCCESS)) {
			mc->mc_flags |= C_EOF;
			return rc;
		}
		mp = mc->mc_pg[mc->mc_top];
		mdb_debug("next page is %zu, key index %u", mp->mp_pgno, mc->mc_ki[mc->mc_top]);
	} else
		mc->mc_ki[mc->mc_top]++;

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

	if (IS_LEAF2(mp)) {
		key->mv_size = mc->mc_db->md_xsize;
		key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
		return MDB_SUCCESS;
	}

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

	if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
		mdb_xcursor_init1(mc, leaf);
	}
	if (data) {
		if (unlikely((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS))
			return rc;

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

	MDB_GET_KEY(leaf, key);
	return MDB_SUCCESS;
}

/** Move the cursor to the previous data item. */
static int
mdb_cursor_prev(MDB_cursor *mc, MDB_val *key, MDB_val *data, MDB_cursor_op op)
{
	MDB_page	*mp;
	MDB_node	*leaf;
	int rc;

	if (!(mc->mc_flags & C_INITIALIZED)) {
		rc = mdb_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 & MDB_DUPSORT) {
		leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
		if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
			if (op == MDB_PREV || op == MDB_PREV_DUP) {
				rc = mdb_cursor_prev(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_PREV);
				if (op != MDB_PREV || rc != MDB_NOTFOUND) {
					if (likely(rc == MDB_SUCCESS)) {
						MDB_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 == MDB_PREV_DUP)
				return MDB_NOTFOUND;
		}
	}

	mdb_debug("cursor_prev: top page is %zu in cursor %p",
		mdb_dbg_pgno(mp), (void *) mc);

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

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

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

	if (IS_LEAF2(mp)) {
		key->mv_size = mc->mc_db->md_xsize;
		key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
		return MDB_SUCCESS;
	}

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

	if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
		mdb_xcursor_init1(mc, leaf);
	}
	if (data) {
		if (unlikely((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS))
			return rc;

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

	MDB_GET_KEY(leaf, key);
	return MDB_SUCCESS;
}

/** Set the cursor on a specific data item. */
static int
mdb_cursor_set(MDB_cursor *mc, MDB_val *key, MDB_val *data,
	MDB_cursor_op op, int *exactp)
{
	int		 rc;
	MDB_page	*mp;
	MDB_node	*leaf = NULL;
	DKBUF;

	if (unlikely(key->mv_size == 0))
		return MDB_BAD_VALSIZE;

	if ( (mc->mc_db->md_flags & MDB_INTEGERKEY)
		&& unlikely( key->mv_size != sizeof(unsigned)
		&& key->mv_size != sizeof(size_t) )) {
		mdb_cassert(mc, ! "key-size is invalid for MDB_INTEGERKEY");
		return MDB_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) {
		MDB_val nodekey;

		mp = mc->mc_pg[mc->mc_top];
		if (!NUMKEYS(mp)) {
			mc->mc_ki[mc->mc_top] = 0;
			return MDB_NOTFOUND;
		}
		if (mp->mp_flags & P_LEAF2) {
			nodekey.mv_size = mc->mc_db->md_xsize;
			nodekey.mv_data = LEAF2KEY(mp, 0, nodekey.mv_size);
		} else {
			leaf = NODEPTR(mp, 0);
			MDB_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.mv_data = LEAF2KEY(mp,
						 nkeys-1, nodekey.mv_size);
				} else {
					leaf = NODEPTR(mp, nkeys-1);
					MDB_GET_KEY2(leaf, nodekey);
				}
				rc = mc->mc_dbx->md_cmp(key, &nodekey);
				if (rc == 0) {
					/* last node was the one we wanted */
					mc->mc_ki[mc->mc_top] = 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.mv_data = LEAF2KEY(mp,
								 mc->mc_ki[mc->mc_top], nodekey.mv_size);
						} else {
							leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
							MDB_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;
					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 */
				mc->mc_ki[mc->mc_top] = nkeys;
				return MDB_NOTFOUND;
			}
		}
		if (!mc->mc_top) {
			/* There are no other pages */
			mc->mc_ki[mc->mc_top] = 0;
			if (op == MDB_SET_RANGE && !exactp) {
				rc = 0;
				goto set1;
			} else
				return MDB_NOTFOUND;
		}
	} else {
		mc->mc_pg[0] = 0;
	}

	rc = mdb_page_search(mc, key, 0);
	if (unlikely(rc != MDB_SUCCESS))
		return rc;

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

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

	if (leaf == NULL) {
		mdb_debug("===> inexact leaf not found, goto sibling");
		if (unlikely((rc = mdb_cursor_sibling(mc, 1)) != MDB_SUCCESS)) {
			mc->mc_flags |= C_EOF;
			return rc;		/* no entries matched */
		}
		mp = mc->mc_pg[mc->mc_top];
		mdb_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 == MDB_SET_RANGE || op == MDB_SET_KEY) {
			key->mv_size = mc->mc_db->md_xsize;
			key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
		}
		return MDB_SUCCESS;
	}

	if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
		mdb_xcursor_init1(mc, leaf);
	}
	if (likely(data)) {
		if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
			if (op == MDB_SET || op == MDB_SET_KEY || op == MDB_SET_RANGE) {
				rc = mdb_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
			} else {
				int ex2, *ex2p;
				if (op == MDB_GET_BOTH) {
					ex2p = &ex2;
					ex2 = 0;
				} else {
					ex2p = NULL;
				}
				rc = mdb_cursor_set(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_SET_RANGE, ex2p);
				if (unlikely(rc != MDB_SUCCESS))
					return rc;
			}
		} else if (op == MDB_GET_BOTH || op == MDB_GET_BOTH_RANGE) {
			MDB_val olddata;
			if (unlikely((rc = mdb_node_read(mc->mc_txn, leaf, &olddata)) != MDB_SUCCESS))
				return rc;
			rc = mc->mc_dbx->md_dcmp(data, &olddata);
			if (rc) {
				if (op == MDB_GET_BOTH || rc > 0)
					return MDB_NOTFOUND;
				rc = 0;
			}
			*data = olddata;

		} else {
			if (mc->mc_xcursor)
				mc->mc_xcursor->mx_cursor.mc_flags &= ~(C_INITIALIZED|C_EOF);
			if (unlikely((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS))
				return rc;
		}
	}

	/* The key already matches in all other cases */
	if (op == MDB_SET_RANGE || op == MDB_SET_KEY)
		MDB_GET_KEY(leaf, key);
	mdb_debug("==> cursor placed on key [%s]", DKEY(key));

	return rc;
}

/** Move the cursor to the first item in the database. */
static int
mdb_cursor_first(MDB_cursor *mc, MDB_val *key, MDB_val *data)
{
	int		 rc;
	MDB_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 = mdb_page_search(mc, NULL, MDB_PS_FIRST);
		if (unlikely(rc != MDB_SUCCESS))
			return rc;
	}
	mdb_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->mv_size = mc->mc_db->md_xsize;
		key->mv_data = LEAF2KEY(mc->mc_pg[mc->mc_top], 0, key->mv_size);
		return MDB_SUCCESS;
	}

	if (likely(data)) {
		if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
			mdb_xcursor_init1(mc, leaf);
			rc = mdb_cursor_first(&mc->mc_xcursor->mx_cursor, data, NULL);
			if (unlikely(rc))
				return rc;
		} else {
			if (unlikely((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS))
				return rc;
		}
	}
	MDB_GET_KEY(leaf, key);
	return MDB_SUCCESS;
}

/** Move the cursor to the last item in the database. */
static int
mdb_cursor_last(MDB_cursor *mc, MDB_val *key, MDB_val *data)
{
	int		 rc;
	MDB_node	*leaf;

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

	if (likely(!(mc->mc_flags & C_EOF))) {

		if (!(mc->mc_flags & C_INITIALIZED) || mc->mc_top) {
			rc = mdb_page_search(mc, NULL, MDB_PS_LAST);
			if (unlikely(rc != MDB_SUCCESS))
				return rc;
		}
		mdb_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->mv_size = mc->mc_db->md_xsize;
		key->mv_data = LEAF2KEY(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], key->mv_size);
		return MDB_SUCCESS;
	}

	if (likely(data)) {
		if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
			mdb_xcursor_init1(mc, leaf);
			rc = mdb_cursor_last(&mc->mc_xcursor->mx_cursor, data, NULL);
			if (unlikely(rc))
				return rc;
		} else {
			if (unlikely((rc = mdb_node_read(mc->mc_txn, leaf, data)) != MDB_SUCCESS))
				return rc;
		}
	}

	MDB_GET_KEY(leaf, key);
	return MDB_SUCCESS;
}

int
mdb_cursor_get(MDB_cursor *mc, MDB_val *key, MDB_val *data,
	MDB_cursor_op op)
{
	int		 rc;
	int		 exact = 0;
	int		 (*mfunc)(MDB_cursor *mc, MDB_val *key, MDB_val *data);

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

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

	if (unlikely(mc->mc_txn->mt_flags & MDB_TXN_BLOCKED))
		return MDB_BAD_TXN;

	switch (op) {
	case MDB_GET_CURRENT:
		if (unlikely(!(mc->mc_flags & C_INITIALIZED))) {
			rc = EINVAL;
		} else {
			MDB_page *mp = mc->mc_pg[mc->mc_top];
			int nkeys = NUMKEYS(mp);
			if (!nkeys || mc->mc_ki[mc->mc_top] >= nkeys) {
				mc->mc_ki[mc->mc_top] = nkeys;
				rc = MDB_NOTFOUND;
				break;
			}
			rc = MDB_SUCCESS;
			if (IS_LEAF2(mp)) {
				key->mv_size = mc->mc_db->md_xsize;
				key->mv_data = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], key->mv_size);
			} else {
				MDB_node *leaf = NODEPTR(mp, mc->mc_ki[mc->mc_top]);
				MDB_GET_KEY(leaf, key);
				if (data) {
					if (F_ISSET(leaf->mn_flags, F_DUPDATA)) {
						rc = mdb_cursor_get(&mc->mc_xcursor->mx_cursor, data, NULL, MDB_GET_CURRENT);
					} else {
						rc = mdb_node_read(mc->mc_txn, leaf, data);
					}
				}
			}
		}
		break;
	case MDB_GET_BOTH:
	case MDB_GET_BOTH_RANGE:
		if (unlikely(data == NULL)) {
			rc = EINVAL;
			break;
		}
		if (unlikely(mc->mc_xcursor == NULL)) {
			rc = MDB_INCOMPATIBLE;
			break;
		}
		/* FALLTHRU */
	case MDB_SET:
	case MDB_SET_KEY:
	case MDB_SET_RANGE:
		if (unlikely(key == NULL)) {
			rc = EINVAL;
		} else {
			rc = mdb_cursor_set(mc, key, data, op,
				op == MDB_SET_RANGE ? NULL : &exact);
		}
		break;
	case MDB_GET_MULTIPLE:
		if (unlikely(data == NULL || !(mc->mc_flags & C_INITIALIZED))) {
			rc = EINVAL;
			break;
		}
		if (unlikely(!(mc->mc_db->md_flags & MDB_DUPFIXED))) {
			rc = MDB_INCOMPATIBLE;
			break;
		}
		rc = MDB_SUCCESS;
		if (!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) ||
			(mc->mc_xcursor->mx_cursor.mc_flags & C_EOF))
			break;
		goto fetchm;
	case MDB_NEXT_MULTIPLE:
		if (unlikely(data == NULL)) {
			rc = EINVAL;
			break;
		}
		if (unlikely(!(mc->mc_db->md_flags & MDB_DUPFIXED))) {
			rc = MDB_INCOMPATIBLE;
			break;
		}
		rc = mdb_cursor_next(mc, key, data, MDB_NEXT_DUP);
		if (rc == MDB_SUCCESS) {
			if (mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) {
				MDB_cursor *mx;
fetchm:
				mx = &mc->mc_xcursor->mx_cursor;
				data->mv_size = NUMKEYS(mx->mc_pg[mx->mc_top]) *
					mx->mc_db->md_xsize;
				data->mv_data = PAGEDATA(mx->mc_pg[mx->mc_top]);
				mx->mc_ki[mx->mc_top] = NUMKEYS(mx->mc_pg[mx->mc_top])-1;
			} else {
				rc = MDB_NOTFOUND;
			}
		}
		break;
	case MDB_PREV_MULTIPLE:
		if (data == NULL) {
			rc = EINVAL;
			break;
		}
		if (!(mc->mc_db->md_flags & MDB_DUPFIXED)) {
			rc = MDB_INCOMPATIBLE;
			break;
		}
		if (!(mc->mc_flags & C_INITIALIZED))
			rc = mdb_cursor_last(mc, key, data);
		else
			rc = MDB_SUCCESS;
		if (rc == MDB_SUCCESS) {
			MDB_cursor *mx = &mc->mc_xcursor->mx_cursor;
			if (mx->mc_flags & C_INITIALIZED) {
				rc = mdb_cursor_sibling(mx, 0);
				if (rc == MDB_SUCCESS)
					goto fetchm;
			} else {
				rc = MDB_NOTFOUND;
			}
		}
		break;
	case MDB_NEXT:
	case MDB_NEXT_DUP:
	case MDB_NEXT_NODUP:
		rc = mdb_cursor_next(mc, key, data, op);
		break;
	case MDB_PREV:
	case MDB_PREV_DUP:
	case MDB_PREV_NODUP:
		rc = mdb_cursor_prev(mc, key, data, op);
		break;
	case MDB_FIRST:
		rc = mdb_cursor_first(mc, key, data);
		break;
	case MDB_FIRST_DUP:
		mfunc = mdb_cursor_first;
	mmove:
		if (unlikely(data == NULL || !(mc->mc_flags & C_INITIALIZED))) {
			rc = EINVAL;
			break;
		}
		if (unlikely(mc->mc_xcursor == NULL)) {
			rc = MDB_INCOMPATIBLE;
			break;
		}
		{
			MDB_node *leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
			if (!F_ISSET(leaf->mn_flags, F_DUPDATA)) {
				MDB_GET_KEY(leaf, key);
				rc = mdb_node_read(mc->mc_txn, leaf, data);
				break;
			}
		}
		if (unlikely(!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED))) {
			rc = EINVAL;
			break;
		}
		rc = mfunc(&mc->mc_xcursor->mx_cursor, data, NULL);
		break;
	case MDB_LAST:
		rc = mdb_cursor_last(mc, key, data);
		break;
	case MDB_LAST_DUP:
		mfunc = mdb_cursor_last;
		goto mmove;
	default:
		mdb_debug("unhandled/unimplemented cursor operation %u", op);
		rc = EINVAL;
		break;
	}

	if (mc->mc_flags & C_DEL)
		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.
 * @param[in] mc The cursor to operate on.
 */
static int
mdb_cursor_touch(MDB_cursor *mc)
{
	int rc = MDB_SUCCESS;

	if (mc->mc_dbi >= CORE_DBS && !(*mc->mc_dbflag & DB_DIRTY)) {
		MDB_cursor mc2;
		MDB_xcursor mcx;
		if (TXN_DBI_CHANGED(mc->mc_txn, mc->mc_dbi))
			return MDB_BAD_DBI;
		mdb_cursor_init(&mc2, mc->mc_txn, MAIN_DBI, &mcx);
		rc = mdb_page_search(&mc2, &mc->mc_dbx->md_name, MDB_PS_MODIFY);
		if (unlikely(rc))
			 return rc;
		*mc->mc_dbflag |= DB_DIRTY;
	}
	mc->mc_top = 0;
	if (mc->mc_snum) {
		do {
			rc = mdb_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 MDB_NOSPILL	0x8000

int
mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
	unsigned flags)
{
	MDB_env		*env;
	MDB_node	*leaf = NULL;
	MDB_page	*fp, *mp, *sub_root = NULL;
	uint16_t	fp_flags;
	MDB_val		xdata, *rdata, dkey, olddata;
	MDB_db dummy;
	int do_sub = 0, insert_key, insert_data;
	unsigned mcount = 0, dcount = 0, nospill;
	size_t nsize;
	int rc, rc2;
	unsigned nflags;
	DKBUF;

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

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

	env = mc->mc_txn->mt_env;

	/* Check this first so counter will always be zero on any
	 * early failures.
	 */
	if (flags & MDB_MULTIPLE) {
		dcount = data[1].mv_size;
		data[1].mv_size = 0;
		if (unlikely(!F_ISSET(mc->mc_db->md_flags, MDB_DUPFIXED)))
			return MDB_INCOMPATIBLE;
	}

	if (flags & MDB_RESERVE) {
		if (unlikely(mc->mc_db->md_flags & (MDB_DUPSORT | MDB_REVERSEDUP)))
			return MDB_INCOMPATIBLE;
	}

	nospill = flags & MDB_NOSPILL;
	flags &= ~MDB_NOSPILL;

	if (unlikely(mc->mc_txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_BLOCKED)))
		return (mc->mc_txn->mt_flags & MDB_TXN_RDONLY) ? EACCES : MDB_BAD_TXN;

	if (unlikely(key->mv_size-1 >= ENV_MAXKEY(env)))
		return MDB_BAD_VALSIZE;

#if SIZE_MAX > MAXDATASIZE
	if (unlikely(data->mv_size > ((mc->mc_db->md_flags & MDB_DUPSORT) ? ENV_MAXKEY(env) : MAXDATASIZE)))
		return MDB_BAD_VALSIZE;
#else
	if ((mc->mc_db->md_flags & MDB_DUPSORT) && unlikely(data->mv_size > ENV_MAXKEY(env)))
		return MDB_BAD_VALSIZE;
#endif

	if ((mc->mc_db->md_flags & MDB_INTEGERKEY)
		&& unlikely(key->mv_size != sizeof(unsigned)
		&& key->mv_size != sizeof(size_t) )) {
		mdb_cassert(mc, ! "key-size is invalid for MDB_INTEGERKEY");
		return MDB_BAD_VALSIZE;
	}

	if ((mc->mc_db->md_flags & MDB_INTEGERDUP)
		&& unlikely(data->mv_size != sizeof(unsigned)
		&& data->mv_size != sizeof(size_t) )) {
		mdb_cassert(mc, ! "data-size is invalid MDB_INTEGERDUP");
		return MDB_BAD_VALSIZE;
	}

	mdb_debug("==> put db %d key [%s], size %zu, data size %zu",
		DDBI(mc), DKEY(key), key ? key->mv_size : 0, data->mv_size);

	dkey.mv_size = 0;

	if (flags == MDB_CURRENT) {
		if (unlikely(!(mc->mc_flags & C_INITIALIZED)))
			return EINVAL;
		rc = MDB_SUCCESS;
	} else 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 = MDB_NO_ROOT;
	} else {
		int exact = 0;
		MDB_val d2;
		if (flags & MDB_APPEND) {
			MDB_val k2;
			rc = mdb_cursor_last(mc, &k2, &d2);
			if (rc == 0) {
				rc = mc->mc_dbx->md_cmp(key, &k2);
				if (rc > 0) {
					rc = MDB_NOTFOUND;
					mc->mc_ki[mc->mc_top]++;
				} else {
					/* new key is <= last key */
					rc = MDB_KEYEXIST;
				}
			}
		} else {
			rc = mdb_cursor_set(mc, key, &d2, MDB_SET, &exact);
		}
		if ((flags & MDB_NOOVERWRITE) && rc == 0) {
			mdb_debug("duplicate key [%s]", DKEY(key));
			*data = d2;
			return MDB_KEYEXIST;
		}
		if (rc && unlikely(rc != MDB_NOTFOUND))
			return rc;
	}

	if (mc->mc_flags & C_DEL)
		mc->mc_flags ^= C_DEL;

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

	if (rc == MDB_NO_ROOT) {
		MDB_page *np;
		/* new database, write a root leaf page */
		mdb_debug("allocating new root leaf page");
		if (unlikely(rc2 = mdb_page_new(mc, P_LEAF, 1, &np))) {
			return rc2;
		}
		mdb_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 & (MDB_DUPSORT|MDB_DUPFIXED)) == MDB_DUPFIXED)
			np->mp_flags |= P_LEAF2;
		mc->mc_flags |= C_INITIALIZED;
	} else {
		/* make sure all cursor pages are writable */
		rc2 = mdb_cursor_touch(mc);
		if (unlikely(rc2))
			return rc2;
	}

	insert_key = insert_data = rc;
	if (insert_key) {
		/* The key does not exist */
		mdb_debug("inserting key at index %i", mc->mc_ki[mc->mc_top]);
		if ((mc->mc_db->md_flags & MDB_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_ksize = data->mv_size; /* used if MDB_DUPFIXED */
			fp->mp_lower = fp->mp_upper = (PAGEHDRSZ-PAGEBASE);
			olddata.mv_size = 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->mv_size != ksize)
				return MDB_BAD_VALSIZE;
			ptr = LEAF2KEY(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top], ksize);
			memcpy(ptr, key->mv_data, 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 short 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 = mdb_update_key(mc, key);
				else
					rc2 = MDB_SUCCESS;
				mc->mc_top += dtop;
				if (rc2)
					return rc2;
			}
			return MDB_SUCCESS;
		}

more:
		leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
		olddata.mv_size = NODEDSZ(leaf);
		olddata.mv_data = NODEDATA(leaf);

		/* DB has dups? */
		if (F_ISSET(mc->mc_db->md_flags, MDB_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;
			mp = fp = xdata.mv_data = 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)) {
				/* Just overwrite the current item */
				if (flags == MDB_CURRENT)
					goto current;

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

				/* Back up original data item */
				dkey.mv_size = olddata.mv_size;
				dkey.mv_data = memcpy(fp+1, olddata.mv_data, olddata.mv_size);

				/* Make sub-page header for the dup items, with dummy body */
				fp->mp_flags = P_LEAF|P_DIRTY|P_SUBP;
				fp->mp_lower = (PAGEHDRSZ-PAGEBASE);
				xdata.mv_size = PAGEHDRSZ + dkey.mv_size + data->mv_size;
				if (mc->mc_db->md_flags & MDB_DUPFIXED) {
					fp->mp_flags |= P_LEAF2;
					fp->mp_ksize = data->mv_size;
					xdata.mv_size += 2 * data->mv_size;	/* leave space for 2 more */
				} else {
					xdata.mv_size += 2 * (sizeof(indx_t) + NODESIZE) +
						(dkey.mv_size & 1) + (data->mv_size & 1);
				}
				fp->mp_upper = xdata.mv_size - PAGEBASE;
				olddata.mv_size = xdata.mv_size; /* 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.mv_data;
				switch (flags) {
				default:
					if (!(mc->mc_db->md_flags & MDB_DUPFIXED)) {
						offset = EVEN(NODESIZE + sizeof(indx_t) +
							data->mv_size);
						break;
					}
					offset = fp->mp_ksize;
					if (SIZELEFT(fp) < offset) {
						offset *= 4; /* space for 4 more */
						break;
					}
					/* FALLTHRU: Big enough MDB_DUPFIXED sub-page */
				case MDB_CURRENT:
					fp->mp_flags |= P_DIRTY;
					COPY_PGNO(fp->mp_pgno, mp->mp_pgno);
					mc->mc_xcursor->mx_cursor.mc_pg[0] = fp;
					flags |= F_DUPDATA;
					goto put_sub;
				}
				xdata.mv_size = olddata.mv_size + offset;
			}

			fp_flags = fp->mp_flags;
			if (NODESIZE + NODEKSZ(leaf) + xdata.mv_size > env->me_nodemax) {
					/* Too big for a sub-page, convert to sub-DB */
					fp_flags &= ~P_SUBP;
prep_subDB:
					if (mc->mc_db->md_flags & MDB_DUPFIXED) {
						fp_flags |= P_LEAF2;
						dummy.md_xsize = fp->mp_ksize;
						dummy.md_flags = MDB_DUPFIXED;
						if (mc->mc_db->md_flags & MDB_INTEGERDUP)
							dummy.md_flags |= MDB_INTEGERKEY;
					} else {
						dummy.md_xsize = 0;
						dummy.md_flags = 0;
					}
					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.mv_size = sizeof(MDB_db);
					xdata.mv_data = &dummy;
					if ((rc = mdb_page_alloc(mc, 1, &mp, MDB_ALLOC_ALL)))
						return rc;
					offset = env->me_psize - olddata.mv_size;
					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_ksize = fp->mp_ksize;
				mp->mp_lower = fp->mp_lower;
				mp->mp_upper = fp->mp_upper + offset;
				if (fp_flags & P_LEAF2) {
					memcpy(PAGEDATA(mp), PAGEDATA(fp), NUMKEYS(fp) * fp->mp_ksize);
				} else {
					memcpy((char *)mp + mp->mp_upper + PAGEBASE, (char *)fp + fp->mp_upper + PAGEBASE,
						olddata.mv_size - fp->mp_upper - PAGEBASE);
					for (i=0; i<NUMKEYS(fp); i++)
						mp->mp_ptrs[i] = fp->mp_ptrs[i] + offset;
				}
			}

			rdata = &xdata;
			flags |= F_DUPDATA;
			do_sub = 1;
			if (!insert_key)
				mdb_node_del(mc, 0);
			goto new_sub;
		}
current:
		/* LMDB passes F_SUBDATA in 'flags' to write a DB record */
		if (unlikely((leaf->mn_flags ^ flags) & F_SUBDATA))
			return MDB_INCOMPATIBLE;
		/* overflow page overwrites need special handling */
		if (F_ISSET(leaf->mn_flags, F_BIGDATA)) {
			MDB_page *omp;
			pgno_t pg;
			int level, ovpages, dpages = OVPAGES(data->mv_size, env->me_psize);

			memcpy(&pg, olddata.mv_data, sizeof(pg));
			if (unlikely((rc2 = mdb_page_get(mc->mc_txn, 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 & MDB_WRITEMAP))) {
					rc = mdb_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 */
						size_t sz = (size_t) env->me_psize * ovpages, off;
						MDB_page *np = mdb_page_malloc(mc->mc_txn, ovpages);
						MDB_ID2 id2;
						if (unlikely(!np))
							return ENOMEM;
						id2.mid = pg;
						id2.mptr = np;
						/* Note - this page is already counted in parent's dirty_room */
						rc2 = mdb_mid2l_insert(mc->mc_txn->mt_u.dirty_list, &id2);
						mdb_cassert(mc, rc2 == 0);
						if (1 || /* LY: Hm, why we should do this differently in dependence from MDB_RESERVE? */
								!(flags & MDB_RESERVE)) {
							/* Copy end of page, adjusting alignment so
							 * compiler may copy words instead of bytes.
							 */
							off = (PAGEHDRSZ + data->mv_size) & -sizeof(size_t);
							memcpy((size_t *)((char *)np + off),
								(size_t *)((char *)omp + off), sz - off);
							sz = PAGEHDRSZ;
						}
						memcpy(np, omp, sz); /* Copy beginning of page */
						omp = np;
					}
					SETDSZ(leaf, data->mv_size);
					if (F_ISSET(flags, MDB_RESERVE))
						data->mv_data = PAGEDATA(omp);
					else
						memcpy(PAGEDATA(omp), data->mv_data, data->mv_size);
					return MDB_SUCCESS;
				}
			}
			if ((rc2 = mdb_ovpage_free(mc, omp)) != MDB_SUCCESS)
				return rc2;
		} else if (data->mv_size == olddata.mv_size) {
			/* 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, MDB_RESERVE))
				data->mv_data = olddata.mv_data;
			else if (!(mc->mc_flags & C_SUB))
				memcpy(olddata.mv_data, data->mv_data, data->mv_size);
			else {
				memcpy(NODEKEY(leaf), key->mv_data, key->mv_size);
				goto fix_parent;
			}
			return MDB_SUCCESS;
		}
		mdb_node_del(mc, 0);
	}

	rdata = data;

new_sub:
	nflags = flags & NODE_ADD_FLAGS;
	nsize = IS_LEAF2(mc->mc_pg[mc->mc_top]) ? key->mv_size : mdb_leaf_size(env, key, rdata);
	if (SIZELEFT(mc->mc_pg[mc->mc_top]) < nsize) {
		if (( flags & (F_DUPDATA|F_SUBDATA)) == F_DUPDATA )
			nflags &= ~MDB_APPEND; /* sub-page may need room to grow */
		if (!insert_key)
			nflags |= MDB_SPLIT_REPLACE;
		rc = mdb_page_split(mc, key, rdata, P_INVALID, nflags);
	} else {
		/* There is room already in this leaf page. */
		rc = mdb_node_add(mc, mc->mc_ki[mc->mc_top], key, rdata, 0, nflags);
		if (likely(rc == 0)) {
			/* Adjust other cursors pointing to mp */
			MDB_cursor *m2, *m3;
			MDB_dbi dbi = mc->mc_dbi;
			unsigned i = mc->mc_top;
			MDB_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 (m3->mc_xcursor && (m3->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED)) {
					MDB_node *n2 = NODEPTR(mp, m3->mc_ki[i]);
					if ((n2->mn_flags & (F_SUBDATA|F_DUPDATA)) == F_DUPDATA)
						m3->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(n2);
				}
			}
		}
	}

	if (likely(rc == MDB_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, new_dupdata;
			size_t ecount;
put_sub:
			xdata.mv_size = 0;
			xdata.mv_data = "";
			leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
			if (flags & MDB_CURRENT) {
				xflags = MDB_CURRENT|MDB_NOSPILL;
			} else {
				mdb_xcursor_init1(mc, leaf);
				xflags = (flags & MDB_NODUPDATA) ?
					MDB_NOOVERWRITE|MDB_NOSPILL : MDB_NOSPILL;
			}
			if (sub_root)
				mc->mc_xcursor->mx_cursor.mc_pg[0] = sub_root;
			new_dupdata = (int)dkey.mv_size;
			/* converted, write the original data first */
			if (dkey.mv_size) {
				rc = mdb_cursor_put(&mc->mc_xcursor->mx_cursor, &dkey, &xdata, xflags);
				if (unlikely(rc))
					goto bad_sub;
				/* we've done our job */
				dkey.mv_size = 0;
			}
			if (!(leaf->mn_flags & F_SUBDATA) || sub_root) {
				/* Adjust other cursors pointing to mp */
				MDB_cursor *m2;
				MDB_xcursor *mx = mc->mc_xcursor;
				unsigned i = mc->mc_top;
				MDB_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]) {
							mdb_xcursor_init2(m2, mx, new_dupdata);
						} else if (!insert_key && m2->mc_ki[i] < nkeys) {
							MDB_node *n2 = NODEPTR(mp, m2->mc_ki[i]);
							if ((n2->mn_flags & (F_SUBDATA|F_DUPDATA)) == F_DUPDATA)
								m2->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(n2);
						}
					}
				}
			}
			ecount = mc->mc_xcursor->mx_db.md_entries;
			if (flags & MDB_APPENDDUP)
				xflags |= MDB_APPEND;
			rc = mdb_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(MDB_db));
			}
			insert_data = mc->mc_xcursor->mx_db.md_entries - ecount;
		}
		/* 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 & MDB_MULTIPLE) {
			if (!rc) {
				mcount++;
				/* let caller know how many succeeded, if any */
				data[1].mv_size = mcount;
				if (mcount < dcount) {
					data[0].mv_data = (char *)data[0].mv_data + data[0].mv_size;
					insert_key = insert_data = 0;
					goto more;
				}
			}
		}
		return rc;
bad_sub:
		if (unlikely(rc == MDB_KEYEXIST))	/* should not happen, we deleted that item */
			rc = MDB_CORRUPTED;
	}
	mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
	return rc;
}

int
mdb_cursor_del(MDB_cursor *mc, unsigned flags)
{
	MDB_node	*leaf;
	MDB_page	*mp;
	int rc;

	if (unlikely(!mc))
		return EINVAL;

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

	if (unlikely(mc->mc_txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_BLOCKED)))
		return (mc->mc_txn->mt_flags & MDB_TXN_RDONLY) ? EACCES : MDB_BAD_TXN;

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

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

	if (unlikely(!(flags & MDB_NOSPILL) && (rc = mdb_page_spill(mc, NULL, NULL))))
		return rc;

	rc = mdb_cursor_touch(mc);
	if (unlikely(rc))
		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 & MDB_NODUPDATA) {
			/* mdb_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 = mdb_cursor_del(&mc->mc_xcursor->mx_cursor, MDB_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(MDB_db));
				} else {
					MDB_cursor *m2;
					/* shrink fake page */
					mdb_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) {
							if (m2->mc_ki[mc->mc_top] == mc->mc_ki[mc->mc_top]) {
								m2->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(leaf);
							} else {
								MDB_node *n2 = NODEPTR(mp, m2->mc_ki[mc->mc_top]);
								if (!(n2->mn_flags & F_SUBDATA))
									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 = mdb_drop0(&mc->mc_xcursor->mx_cursor, 0);
			if (unlikely(rc))
				goto fail;
		}
	}
	/* LMDB passes F_SUBDATA in 'flags' to delete a DB record */
	else if (unlikely((leaf->mn_flags ^ flags) & F_SUBDATA)) {
		rc = MDB_INCOMPATIBLE;
		goto fail;
	}

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

		memcpy(&pg, NODEDATA(leaf), sizeof(pg));
		if (unlikely((rc = mdb_page_get(mc->mc_txn, pg, &omp, NULL)) ||
			(rc = mdb_ovpage_free(mc, omp))))
			goto fail;
	}

del_key:
	return mdb_cursor_del0(mc);

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

/** Allocate and initialize new pages for a database.
 * @param[in] mc a cursor on the database being added to.
 * @param[in] flags flags defining what type of page is being allocated.
 * @param[in] num the number of pages to allocate. This is usually 1,
 * unless allocating overflow pages for a large record.
 * @param[out] mp Address of a page, or NULL on failure.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_new(MDB_cursor *mc, uint32_t flags, int num, MDB_page **mp)
{
	MDB_page	*np;
	int rc;

	if (unlikely((rc = mdb_page_alloc(mc, num, &np, MDB_ALLOC_ALL))))
		return rc;
	mdb_debug("allocated new mpage %zu, page size %u",
		np->mp_pgno, mc->mc_txn->mt_env->me_psize);
	np->mp_flags = flags | P_DIRTY;
	np->mp_lower = (PAGEHDRSZ-PAGEBASE);
	np->mp_upper = mc->mc_txn->mt_env->me_psize - PAGEBASE;

	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 0;
}

/** 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 #MDB_node headers.
 * @param[in] env The environment handle.
 * @param[in] key The key for the node.
 * @param[in] data The data for the node.
 * @return The number of bytes needed to store the node.
 */
static MDB_INLINE size_t
mdb_leaf_size(MDB_env *env, MDB_val *key, MDB_val *data)
{
	size_t		 sz;

	sz = LEAFSIZE(key, data);
	if (sz > env->me_nodemax) {
		/* put on overflow page */
		sz -= data->mv_size - 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 #MDB_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 #MDB_node headers.
 * @param[in] env The environment handle.
 * @param[in] key The key for the node.
 * @return The number of bytes needed to store the node.
 */
static MDB_INLINE size_t
mdb_branch_size(MDB_env *env, MDB_val *key)
{
	size_t		 sz;

	sz = INDXSIZE(key);
	if (sz > env->me_nodemax) {
		/* put on overflow page */
		/* not implemented */
		/* sz -= key->size - sizeof(pgno_t); */
	}

	return sz + sizeof(indx_t);
}

/** Add a node to the page pointed to by the cursor.
 * @param[in] mc The cursor for this operation.
 * @param[in] indx The index on the page where the new node should be added.
 * @param[in] key The key for the new node.
 * @param[in] data The data for the new node, if any.
 * @param[in] pgno The page number, if adding a branch node.
 * @param[in] flags Flags for the node.
 * @return 0 on success, non-zero on failure. Possible errors are:
 * <ul>
 *	<li>ENOMEM - failed to allocate overflow pages for the node.
 *	<li>MDB_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.
 * </ul>
 */
static int
mdb_node_add(MDB_cursor *mc, indx_t indx,
	MDB_val *key, MDB_val *data, pgno_t pgno, unsigned flags)
{
	unsigned	 i;
	size_t		 node_size = NODESIZE;
	ssize_t		 room;
	indx_t		 ofs;
	MDB_node	*node;
	MDB_page	*mp = mc->mc_pg[mc->mc_top];
	MDB_page	*ofp = NULL;		/* overflow page */
	void		*ndata;
	DKBUF;

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

	mdb_debug("add to %s %spage %zu index %i, data size %zu key size %zu [%s]",
		IS_LEAF(mp) ? "leaf" : "branch",
		IS_SUBP(mp) ? "sub-" : "",
		mdb_dbg_pgno(mp), indx, data ? data->mv_size : 0,
		key ? key->mv_size : 0, key ? DKEY(key) : "null");

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

		/* Just using these for counting */
		mp->mp_lower += sizeof(indx_t);
		mp->mp_upper -= ksize - sizeof(indx_t);
		return MDB_SUCCESS;
	}

	room = (ssize_t)SIZELEFT(mp) - (ssize_t)sizeof(indx_t);
	if (key != NULL)
		node_size += key->mv_size;
	if (IS_LEAF(mp)) {
		mdb_cassert(mc, key && data);
		if (F_ISSET(flags, F_BIGDATA)) {
			/* Data already on overflow page. */
			node_size += sizeof(pgno_t);
		} else if (node_size + data->mv_size > mc->mc_txn->mt_env->me_nodemax) {
			int ovpages = OVPAGES(data->mv_size, mc->mc_txn->mt_env->me_psize);
			int rc;
			/* Put data on overflow page. */
			mdb_debug("data size is %zu, node would be %zu, put data on overflow page",
				data->mv_size, node_size+data->mv_size);
			node_size = EVEN(node_size + sizeof(pgno_t));
			if ((ssize_t)node_size > room)
				goto full;
			if ((rc = mdb_page_new(mc, P_OVERFLOW, ovpages, &ofp)))
				return rc;
			mdb_debug("allocated overflow page %zu", ofp->mp_pgno);
			flags |= F_BIGDATA;
			goto update;
		} else {
			node_size += data->mv_size;
		}
	}
	node_size = EVEN(node_size);
	if (unlikely((ssize_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. */
	ofs = mp->mp_upper - node_size;
	mdb_cassert(mc, ofs >= mp->mp_lower + sizeof(indx_t));
	mp->mp_ptrs[indx] = ofs;
	mp->mp_upper = ofs;
	mp->mp_lower += sizeof(indx_t);

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

	if (key)
		memcpy(NODEKEY(node), key->mv_data, key->mv_size);

	if (IS_LEAF(mp)) {
		ndata = NODEDATA(node);
		if (ofp == NULL) {
			if (F_ISSET(flags, F_BIGDATA))
				memcpy(ndata, data->mv_data, sizeof(pgno_t));
			else if (F_ISSET(flags, MDB_RESERVE))
				data->mv_data = ndata;
			else
				memcpy(ndata, data->mv_data, data->mv_size);
		} else {
			memcpy(ndata, &ofp->mp_pgno, sizeof(pgno_t));
			ndata = PAGEDATA(ofp);
			if (F_ISSET(flags, MDB_RESERVE))
				data->mv_data = ndata;
			else
				memcpy(ndata, data->mv_data, data->mv_size);
		}
	}

	return MDB_SUCCESS;

full:
	mdb_debug("not enough room in page %zu, got %u ptrs",
		mdb_dbg_pgno(mp), NUMKEYS(mp));
	mdb_debug("upper-lower = %u - %u = %zd", mp->mp_upper,mp->mp_lower,room);
	mdb_debug("node size = %zu", node_size);
	mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
	return MDB_PAGE_FULL;
}

/** Delete the specified node from a page.
 * @param[in] mc Cursor pointing to the node to delete.
 * @param[in] ksize The size of a node. Only used if the page is
 * part of a #MDB_DUPFIXED database.
 */
static void
mdb_node_del(MDB_cursor *mc, int ksize)
{
	MDB_page *mp = mc->mc_pg[mc->mc_top];
	indx_t	indx = mc->mc_ki[mc->mc_top];
	unsigned	 sz;
	indx_t		 i, j, numkeys, ptr;
	MDB_node	*node;
	char		*base;

	mdb_debug("delete node %u on %s page %zu", indx,
		IS_LEAF(mp) ? "leaf" : "branch", mdb_dbg_pgno(mp));
	numkeys = NUMKEYS(mp);
	mdb_cassert(mc, indx < numkeys);

	if (IS_LEAF2(mp)) {
		int x = numkeys - 1 - indx;
		base = LEAF2KEY(mp, indx, ksize);
		if (x)
			memmove(base, base + ksize, x * ksize);
		mp->mp_lower -= sizeof(indx_t);
		mp->mp_upper += ksize - sizeof(indx_t);
		return;
	}

	node = NODEPTR(mp, indx);
	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)
				mp->mp_ptrs[j] += sz;
			j++;
		}
	}

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

	mp->mp_lower -= sizeof(indx_t);
	mp->mp_upper += sz;
}

/** Compact the main page after deleting a node on a subpage.
 * @param[in] mp The main page to operate on.
 * @param[in] indx The index of the subpage on the main page.
 */
static void
mdb_node_shrink(MDB_page *mp, indx_t indx)
{
	MDB_node *node;
	MDB_page *sp, *xp;
	char *base;
	indx_t delta, nsize, len, ptr;
	int i;

	node = NODEPTR(mp, indx);
	sp = (MDB_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 = (MDB_page *)((char *)sp + delta); /* destination subpage */
		for (i = NUMKEYS(sp); --i >= 0; )
			xp->mp_ptrs[i] = sp->mp_ptrs[i] - delta;
		len = PAGEHDRSZ;
	}
	sp->mp_upper = sp->mp_lower;
	COPY_PGNO(sp->mp_pgno, mp->mp_pgno);
	SETDSZ(node, nsize);

	/* Shift <lower nodes...initial part of subpage> upward */
	base = (char *)mp + mp->mp_upper + PAGEBASE;
	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)
			mp->mp_ptrs[i] += delta;
	}
	mp->mp_upper += 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.
 * @param[in] mc The main cursor whose sorted-dups cursor is to be initialized.
 */
static void
mdb_xcursor_init0(MDB_cursor *mc)
{
	MDB_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.mv_size = 0;
	mx->mx_dbx.md_name.mv_data = NULL;
	mx->mx_dbx.md_cmp = mc->mc_dbx->md_dcmp;
	mx->mx_dbx.md_dcmp = NULL;
	mx->mx_dbx.md_rel = mc->mc_dbx->md_rel;
}

/** Final setup of a sorted-dups cursor.
 *	Sets up the fields that depend on the data from the main cursor.
 * @param[in] mc The main cursor whose sorted-dups cursor is to be initialized.
 * @param[in] node The data containing the #MDB_db record for the
 * sorted-dup database.
 */
static void
mdb_xcursor_init1(MDB_cursor *mc, MDB_node *node)
{
	MDB_xcursor *mx = mc->mc_xcursor;

	if (node->mn_flags & F_SUBDATA) {
		memcpy(&mx->mx_db, NODEDATA(node), sizeof(MDB_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 {
		MDB_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);
		COPY_PGNO(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 & MDB_DUPFIXED) {
			mx->mx_db.md_flags = MDB_DUPFIXED;
			mx->mx_db.md_xsize = fp->mp_ksize;
			if (mc->mc_db->md_flags & MDB_INTEGERDUP)
				mx->mx_db.md_flags |= MDB_INTEGERKEY;
		}
	}
	mdb_debug("Sub-db -%u root page %zu", mx->mx_cursor.mc_dbi,
		mx->mx_db.md_root);
	mx->mx_dbflag = DB_VALID|DB_USRVALID|DB_DIRTY; /* DB_DIRTY guides mdb_cursor_touch */
/* #if UINT_MAX < SIZE_MAX
	if (mx->mx_dbx.md_cmp == mdb_cmp_int && mx->mx_db.md_pad == sizeof(size_t))
		mx->mx_dbx.md_cmp = mdb_cmp_clong;
#endif */
	mc->mc_signature = MDBX_MC_SIGNATURE;
}


/** 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.
 * @param[in] mc The main cursor whose sorted-dups cursor is to be fixed up.
 * @param[in] src_mx The xcursor of an up-to-date cursor.
 * @param[in] new_dupdata True if converting from a non-#F_DUPDATA item.
 */
static void
mdb_xcursor_init2(MDB_cursor *mc, MDB_xcursor *src_mx, int new_dupdata)
{
	MDB_xcursor *mx = mc->mc_xcursor;

	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_DIRTY; /* DB_DIRTY guides mdb_cursor_touch */
#if UINT_MAX < SIZE_MAX
		mx->mx_dbx.md_cmp = src_mx->mx_dbx.md_cmp;
#endif
	} 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];
	mdb_debug("Sub-db -%u root page %zu", mx->mx_cursor.mc_dbi,
		mx->mx_db.md_root);
}

/** Initialize a cursor for a given transaction and database. */
static void
mdb_cursor_init(MDB_cursor *mc, MDB_txn *txn, MDB_dbi dbi, MDB_xcursor *mx)
{
	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;
	if (txn->mt_dbs[dbi].md_flags & MDB_DUPSORT) {
		mdb_tassert(txn, mx != NULL);
		mx->mx_cursor.mc_signature = MDBX_MC_SIGNATURE;
		mc->mc_xcursor = mx;
		mdb_xcursor_init0(mc);
	} else {
		mc->mc_xcursor = NULL;
	}
	if (*mc->mc_dbflag & DB_STALE) {
		mdb_page_search(mc, NULL, MDB_PS_ROOTONLY);
	}
	mc->mc_signature = MDBX_MC_SIGNATURE;
}

int
mdb_cursor_open(MDB_txn *txn, MDB_dbi dbi, MDB_cursor **ret)
{
	MDB_cursor	*mc;
	size_t size = sizeof(MDB_cursor);

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

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

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

	if (unlikely(txn->mt_flags & MDB_TXN_BLOCKED))
		return MDB_BAD_TXN;

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

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

	if (likely((mc = malloc(size)) != NULL)) {
		mdb_cursor_init(mc, txn, dbi, (MDB_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 ENOMEM;
	}

	*ret = mc;

	return MDB_SUCCESS;
}

int
mdb_cursor_renew(MDB_txn *txn, MDB_cursor *mc)
{
	if (unlikely(!mc || !txn))
		return EINVAL;

	if (unlikely(txn->mt_signature != MDBX_MT_SIGNATURE
			|| mc->mc_signature != MDBX_MC_SIGNATURE))
		return MDB_VERSION_MISMATCH;

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

	if (unlikely((mc->mc_flags & C_UNTRACK) || txn->mt_cursors))
		return EINVAL;

	if (unlikely(txn->mt_flags & MDB_TXN_BLOCKED))
		return MDB_BAD_TXN;

	mdb_cursor_init(mc, txn, mc->mc_dbi, mc->mc_xcursor);
	return MDB_SUCCESS;
}

/* Return the count of duplicate data items for the current key */
int
mdb_cursor_count(MDB_cursor *mc, size_t *countp)
{
	MDB_node	*leaf;

	if (unlikely(mc == NULL || countp == NULL))
		return EINVAL;

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

	if (unlikely(mc->mc_xcursor == NULL))
		return MDB_INCOMPATIBLE;

	if (unlikely(mc->mc_txn->mt_flags & MDB_TXN_BLOCKED))
		return MDB_BAD_TXN;

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

	if (unlikely(!mc->mc_snum || (mc->mc_flags & C_EOF)))
		return MDB_NOTFOUND;

	leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
	if (!F_ISSET(leaf->mn_flags, F_DUPDATA)) {
		*countp = 1;
	} else {
		if (unlikely(!(mc->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED)))
			return EINVAL;

		*countp = mc->mc_xcursor->mx_db.md_entries;
	}
	return MDB_SUCCESS;
}

void
mdb_cursor_close(MDB_cursor *mc)
{
	if (mc) {
		mdb_ensure(NULL, mc->mc_signature == MDBX_MC_SIGNATURE);
		if (!mc->mc_backup) {
			/* remove from txn, if tracked */
			if ((mc->mc_flags & C_UNTRACK) && mc->mc_txn->mt_cursors) {
				MDB_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);
		}
	}
}

MDB_txn *
mdb_cursor_txn(MDB_cursor *mc)
{
	if (unlikely(!mc || mc->mc_signature != MDBX_MC_SIGNATURE))
		return NULL;
	return mc->mc_txn;
}

MDB_dbi
mdb_cursor_dbi(MDB_cursor *mc)
{
	if (unlikely(!mc || mc->mc_signature != MDBX_MC_SIGNATURE))
		return INT_MIN;
	return mc->mc_dbi;
}

/** Replace the key for a branch node with a new key.
 * @param[in] mc Cursor pointing to the node to operate on.
 * @param[in] key The new key to use.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_update_key(MDB_cursor *mc, MDB_val *key)
{
	MDB_page		*mp;
	MDB_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];
	{
		MDB_val	k2;
		char kbuf2[DKBUF_MAXKEYSIZE*2+1];
		k2.mv_data = NODEKEY(node);
		k2.mv_size = node->mn_ksize;
		mdb_debug("update key %u (ofs %u) [%s] to [%s] on page %zu",
			indx, ptr,
			mdb_dkey(&k2, kbuf2),
			DKEY(key),
			mp->mp_pgno);
	}

	/* Sizes must be 2-byte aligned. */
	ksize = EVEN(key->mv_size);
	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 */
			mdb_debug("Not enough room, delta = %d, splitting...", delta);
			pgno = NODEPGNO(node);
			mdb_node_del(mc, 0);
			return mdb_page_split(mc, key, NULL, pgno, MDB_SPLIT_REPLACE);
		}

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

		base = (char *)mp + mp->mp_upper + PAGEBASE;
		len = ptr - mp->mp_upper + NODESIZE;
		memmove(base - delta, base, len);
		mp->mp_upper -= delta;

		node = NODEPTR(mp, indx);
	}

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

	if (key->mv_size)
		memcpy(NODEKEY(node), key->mv_data, key->mv_size);

	return MDB_SUCCESS;
}

static void
mdb_cursor_copy(const MDB_cursor *csrc, MDB_cursor *cdst);

/** Perform \b act while tracking temporary cursor \b mn */
#define WITH_CURSOR_TRACKING(mn, act) do { \
	MDB_cursor dummy, *tracked, **tp = &(mn).mc_txn->mt_cursors[mn.mc_dbi]; \
	if ((mn).mc_flags & C_SUB) { \
		dummy.mc_flags = C_INITIALIZED; \
		dummy.mc_xcursor = (MDB_xcursor *)&(mn);	\
		tracked = &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
mdb_node_move(MDB_cursor *csrc, MDB_cursor *cdst, int fromleft)
{
	MDB_node		*srcnode;
	MDB_val		 key, data;
	pgno_t	srcpg;
	MDB_cursor mn;
	int			 rc;
	unsigned short flags;

	DKBUF;

	/* Mark src and dst as dirty. */
	if (unlikely((rc = mdb_page_touch(csrc)) ||
		(rc = mdb_page_touch(cdst))))
		return rc;

	if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
		key.mv_size = csrc->mc_db->md_xsize;
		key.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], csrc->mc_ki[csrc->mc_top], key.mv_size);
		data.mv_size = 0;
		data.mv_data = NULL;
		srcpg = 0;
		flags = 0;
	} else {
		srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], csrc->mc_ki[csrc->mc_top]);
		mdb_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;
			MDB_node *s2;
			/* must find the lowest key below src */
			rc = mdb_page_search_lowest(csrc);
			if (unlikely(rc))
				return rc;
			if (IS_LEAF2(csrc->mc_pg[csrc->mc_top])) {
				key.mv_size = csrc->mc_db->md_xsize;
				key.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], 0, key.mv_size);
			} else {
				s2 = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);
				key.mv_size = NODEKSZ(s2);
				key.mv_data = NODEKEY(s2);
			}
			csrc->mc_snum = snum--;
			csrc->mc_top = snum;
		} else {
			key.mv_size = NODEKSZ(srcnode);
			key.mv_data = NODEKEY(srcnode);
		}
		data.mv_size = NODEDSZ(srcnode);
		data.mv_data = 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;
		MDB_node *s2;
		MDB_val bkey;
		/* must find the lowest key below dst */
		mdb_cursor_copy(cdst, &mn);
		rc = mdb_page_search_lowest(&mn);
		if (unlikely(rc))
			return rc;
		if (IS_LEAF2(mn.mc_pg[mn.mc_top])) {
			bkey.mv_size = mn.mc_db->md_xsize;
			bkey.mv_data = LEAF2KEY(mn.mc_pg[mn.mc_top], 0, bkey.mv_size);
		} else {
			s2 = NODEPTR(mn.mc_pg[mn.mc_top], 0);
			bkey.mv_size = NODEKSZ(s2);
			bkey.mv_data = NODEKEY(s2);
		}
		mn.mc_snum = snum--;
		mn.mc_top = snum;
		mn.mc_ki[snum] = 0;
		rc = mdb_update_key(&mn, &bkey);
		if (unlikely(rc))
			return rc;
	}

	mdb_debug("moving %s node %u [%s] on page %zu to node %u on page %zu",
		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 = mdb_node_add(cdst, cdst->mc_ki[cdst->mc_top], &key, &data, srcpg, flags);
	if (unlikely(rc != MDB_SUCCESS))
		return rc;

	/* Delete the node from the source page.
	 */
	mdb_node_del(csrc, key.mv_size);

	{
		/* Adjust other cursors pointing to mp */
		MDB_cursor *m2, *m3;
		MDB_dbi dbi = csrc->mc_dbi;
		MDB_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 (m3->mc_xcursor && (m3->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) &&
					IS_LEAF(mps)) {
					MDB_node *node = NODEPTR(m3->mc_pg[csrc->mc_top], m3->mc_ki[csrc->mc_top]);
					if ((node->mn_flags & (F_DUPDATA|F_SUBDATA)) == F_DUPDATA)
						m3->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(node);
				}
			}
		} 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 (m3->mc_xcursor && (m3->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) &&
						IS_LEAF(mps)) {
						MDB_node *node = NODEPTR(m3->mc_pg[csrc->mc_top], m3->mc_ki[csrc->mc_top]);
						if ((node->mn_flags & (F_DUPDATA|F_SUBDATA)) == F_DUPDATA)
							m3->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(node);
					}
				}
			}
		}
	}

	/* 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.mv_data = LEAF2KEY(csrc->mc_pg[csrc->mc_top], 0, key.mv_size);
			} else {
				srcnode = NODEPTR(csrc->mc_pg[csrc->mc_top], 0);
				key.mv_size = NODEKSZ(srcnode);
				key.mv_data = NODEKEY(srcnode);
			}
			mdb_debug("update separator for source page %zu to [%s]",
				csrc->mc_pg[csrc->mc_top]->mp_pgno, DKEY(&key));
			mdb_cursor_copy(csrc, &mn);
			mn.mc_snum--;
			mn.mc_top--;
			/* We want mdb_rebalance to find mn when doing fixups */
			WITH_CURSOR_TRACKING(mn, rc = mdb_update_key(&mn, &key));
			if (unlikely(rc != MDB_SUCCESS))
				return rc;
		}
		if (IS_BRANCH(csrc->mc_pg[csrc->mc_top])) {
			MDB_val	 nullkey;
			indx_t	ix = csrc->mc_ki[csrc->mc_top];
			nullkey.mv_size = 0;
			csrc->mc_ki[csrc->mc_top] = 0;
			rc = mdb_update_key(csrc, &nullkey);
			csrc->mc_ki[csrc->mc_top] = ix;
			mdb_cassert(csrc, rc == MDB_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.mv_data = LEAF2KEY(cdst->mc_pg[cdst->mc_top], 0, key.mv_size);
			} else {
				srcnode = NODEPTR(cdst->mc_pg[cdst->mc_top], 0);
				key.mv_size = NODEKSZ(srcnode);
				key.mv_data = NODEKEY(srcnode);
			}
			mdb_debug("update separator for destination page %zu to [%s]",
				cdst->mc_pg[cdst->mc_top]->mp_pgno, DKEY(&key));
			mdb_cursor_copy(cdst, &mn);
			mn.mc_snum--;
			mn.mc_top--;
			/* We want mdb_rebalance to find mn when doing fixups */
			WITH_CURSOR_TRACKING(mn, rc = mdb_update_key(&mn, &key));
			if (unlikely(rc != MDB_SUCCESS))
				return rc;
		}
		if (IS_BRANCH(cdst->mc_pg[cdst->mc_top])) {
			MDB_val	 nullkey;
			indx_t	ix = cdst->mc_ki[cdst->mc_top];
			nullkey.mv_size = 0;
			cdst->mc_ki[cdst->mc_top] = 0;
			rc = mdb_update_key(cdst, &nullkey);
			cdst->mc_ki[cdst->mc_top] = ix;
			mdb_cassert(cdst, rc == MDB_SUCCESS);
		}
	}

	return MDB_SUCCESS;
}

/** Merge one page into another.
 *  The nodes from the page pointed to by \b csrc will
 *	be copied to the page pointed to by \b cdst and then
 *	the \b csrc page will be freed.
 * @param[in] csrc Cursor pointing to the source page.
 * @param[in] cdst Cursor pointing to the destination page.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_merge(MDB_cursor *csrc, MDB_cursor *cdst)
{
	MDB_page	*psrc, *pdst;
	MDB_node	*srcnode;
	MDB_val		 key, data;
	unsigned	 nkeys;
	int			 rc;
	indx_t		 i, j;

	psrc = csrc->mc_pg[csrc->mc_top];
	pdst = cdst->mc_pg[cdst->mc_top];

	mdb_debug("merging page %zu into %zu", psrc->mp_pgno, pdst->mp_pgno);

	mdb_cassert(csrc, csrc->mc_snum > 1);	/* can't merge root page */
	mdb_cassert(csrc, cdst->mc_snum > 1);

	/* Mark dst as dirty. */
	if (unlikely(rc = mdb_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.mv_size = csrc->mc_db->md_xsize;
		key.mv_data = PAGEDATA(psrc);
		for (i = 0; i < NUMKEYS(psrc); i++, j++) {
			rc = mdb_node_add(cdst, j, &key, NULL, 0, 0);
			if (unlikely(rc != MDB_SUCCESS))
				return rc;
			key.mv_data = (char *)key.mv_data + key.mv_size;
		}
	} else {
		for (i = 0; i < NUMKEYS(psrc); i++, j++) {
			srcnode = NODEPTR(psrc, i);
			if (i == 0 && IS_BRANCH(psrc)) {
				MDB_cursor mn;
				MDB_node *s2;
				mdb_cursor_copy(csrc, &mn);
				mn.mc_xcursor = NULL;
				/* must find the lowest key below src */
				rc = mdb_page_search_lowest(&mn);
				if (unlikely(rc))
					return rc;
				if (IS_LEAF2(mn.mc_pg[mn.mc_top])) {
					key.mv_size = mn.mc_db->md_xsize;
					key.mv_data = LEAF2KEY(mn.mc_pg[mn.mc_top], 0, key.mv_size);
				} else {
					s2 = NODEPTR(mn.mc_pg[mn.mc_top], 0);
					key.mv_size = NODEKSZ(s2);
					key.mv_data = NODEKEY(s2);
				}
			} else {
				key.mv_size = srcnode->mn_ksize;
				key.mv_data = NODEKEY(srcnode);
			}

			data.mv_size = NODEDSZ(srcnode);
			data.mv_data = NODEDATA(srcnode);
			rc = mdb_node_add(cdst, j, &key, &data, NODEPGNO(srcnode), srcnode->mn_flags);
			if (unlikely(rc != MDB_SUCCESS))
				return rc;
		}
	}

	mdb_debug("dst page %zu 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--;
	mdb_node_del(csrc, 0);
	if (csrc->mc_ki[csrc->mc_top] == 0) {
		key.mv_size = 0;
		rc = mdb_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 = mdb_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 */
		MDB_cursor *m2, *m3;
		MDB_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;
				m3->mc_ki[top] += 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 (m3->mc_xcursor && (m3->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) &&
				IS_LEAF(psrc)) {
				MDB_node *node = NODEPTR(m3->mc_pg[top], m3->mc_ki[top]);
				if ((node->mn_flags & (F_DUPDATA|F_SUBDATA)) == F_DUPDATA)
					m3->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(node);
			}
		}
	}
	{
		unsigned snum = cdst->mc_snum;
		uint16_t depth = cdst->mc_db->md_depth;
		mdb_cursor_pop(cdst);
		rc = mdb_rebalance(cdst);
		/* Did the tree height change? */
		if (depth != cdst->mc_db->md_depth)
			snum += cdst->mc_db->md_depth - depth;
		cdst->mc_snum = snum;
		cdst->mc_top = snum-1;
	}
	return rc;
}

/** Copy the contents of a cursor.
 * @param[in] csrc The cursor to copy from.
 * @param[out] cdst The cursor to copy to.
 */
static void
mdb_cursor_copy(const MDB_cursor *csrc, MDB_cursor *cdst)
{
	unsigned i;

	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.
 * @param[in] mc Cursor pointing to the page where rebalancing
 * should begin.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_rebalance(MDB_cursor *mc)
{
	MDB_node	*node;
	int rc, fromleft;
	unsigned ptop, minkeys, thresh;
	MDB_cursor	mn;
	indx_t oldki;

	if (IS_BRANCH(mc->mc_pg[mc->mc_top])) {
		minkeys = 2;
		thresh = 1;
	} else {
		minkeys = 1;
		thresh = FILL_THRESHOLD;
	}
	mdb_debug("rebalancing %s page %zu (has %u keys, %.1f%% full)",
		IS_LEAF(mc->mc_pg[mc->mc_top]) ? "leaf" : "branch",
		mdb_dbg_pgno(mc->mc_pg[mc->mc_top]), 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) {
		mdb_debug("no need to rebalance page %zu, above fill threshold",
			mdb_dbg_pgno(mc->mc_pg[mc->mc_top]));
		return MDB_SUCCESS;
	}

	if (mc->mc_snum < 2) {
		MDB_page *mp = mc->mc_pg[0];
		if (IS_SUBP(mp)) {
			mdb_debug("Can't rebalance a subpage, ignoring");
			return MDB_SUCCESS;
		}
		if (NUMKEYS(mp) == 0) {
			mdb_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 = mdb_midl_append(&mc->mc_txn->mt_free_pgs, 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;
			{
				MDB_cursor *m2, *m3;
				MDB_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;
			mdb_debug("collapsing root page!");
			rc = mdb_midl_append(&mc->mc_txn->mt_free_pgs, mp->mp_pgno);
			if (unlikely(rc))
				return rc;
			mc->mc_db->md_root = NODEPGNO(NODEPTR(mp, 0));
			rc = mdb_page_get(mc->mc_txn,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 */
				MDB_cursor *m2, *m3;
				MDB_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
			mdb_debug("root page doesn't need rebalancing");
		return MDB_SUCCESS;
	}

	/* The parent (branch page) must have at least 2 pointers,
	 * otherwise the tree is invalid.
	 */
	ptop = mc->mc_top-1;
	mdb_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.
	 */
	mdb_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.
		 */
		mdb_debug("reading right neighbor");
		mn.mc_ki[ptop]++;
		node = NODEPTR(mc->mc_pg[ptop], mn.mc_ki[ptop]);
		rc = mdb_page_get(mc->mc_txn,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.
		 */
		mdb_debug("reading left neighbor");
		mn.mc_ki[ptop]--;
		node = NODEPTR(mc->mc_pg[ptop], mn.mc_ki[ptop]);
		rc = mdb_page_get(mc->mc_txn,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;
	}

	mdb_debug("found neighbor page %zu (%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 = mdb_node_move(&mn, mc, fromleft);
		if (fromleft) {
			/* if we inserted on left, bump position up */
			oldki++;
		}
	} else {
		if (!fromleft) {
			rc = mdb_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 mdb_rebalance to find mn when doing fixups */
			WITH_CURSOR_TRACKING(mn,
				rc = mdb_page_merge(mc, &mn));
			mdb_cursor_copy(&mn, mc);
		}
		mc->mc_flags &= ~C_EOF;
	}
	mc->mc_ki[mc->mc_top] = oldki;
	return rc;
}

/** Complete a delete operation started by #mdb_cursor_del(). */
static int
mdb_cursor_del0(MDB_cursor *mc)
{
	int rc;
	MDB_page *mp;
	indx_t ki;
	unsigned nkeys;
	MDB_cursor *m2, *m3;
	MDB_dbi dbi = mc->mc_dbi;

	ki = mc->mc_ki[mc->mc_top];
	mp = mc->mc_pg[mc->mc_top];
	mdb_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;
				} else if (m3->mc_ki[mc->mc_top] > ki) {
					m3->mc_ki[mc->mc_top]--;
				}
				if (m3->mc_xcursor && (m3->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED)) {
					MDB_node *node = NODEPTR(m3->mc_pg[mc->mc_top], m3->mc_ki[mc->mc_top]);
					if ((node->mn_flags & (F_DUPDATA|F_SUBDATA)) == F_DUPDATA)
						m3->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(node);
				}
			}
		}
	}
	rc = mdb_rebalance(mc);

	if (likely(rc == MDB_SUCCESS)) {
		/* DB is totally empty now, just bail out.
		 * Other cursors adjustments were already done
		 * by mdb_rebalance and aren't needed here.
		 */
		if (!mc->mc_snum)
			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 = mdb_cursor_sibling(m3, 1);
						if (rc == MDB_NOTFOUND) {
							m3->mc_flags |= C_EOF;
							rc = MDB_SUCCESS;
							continue;
						}
					}
					if (mc->mc_db->md_flags & MDB_DUPSORT) {
						MDB_node *node = NODEPTR(m3->mc_pg[m3->mc_top], m3->mc_ki[m3->mc_top]);
						if (node->mn_flags & F_DUPDATA) {
							mdb_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 |= MDB_TXN_ERROR;
	return rc;
}

int
mdb_del(MDB_txn *txn, MDB_dbi dbi,
	MDB_val *key, MDB_val *data)
{
	if (unlikely(!key || !txn))
		return EINVAL;

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

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

	if (unlikely(txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_BLOCKED)))
		return (txn->mt_flags & MDB_TXN_RDONLY) ? EACCES : MDB_BAD_TXN;

	if (!F_ISSET(txn->mt_dbs[dbi].md_flags, MDB_DUPSORT)) {
		/* must ignore any data */
		data = NULL;
	}

	return mdb_del0(txn, dbi, key, data, 0);
}

static int
mdb_del0(MDB_txn *txn, MDB_dbi dbi,
	MDB_val *key, MDB_val *data, unsigned flags)
{
	MDB_cursor mc;
	MDB_xcursor mx;
	MDB_cursor_op op;
	MDB_val rdata, *xdata;
	int	rc, exact = 0;
	DKBUF;

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

	mdb_cursor_init(&mc, txn, dbi, &mx);

	if (data) {
		op = MDB_GET_BOTH;
		rdata = *data;
		xdata = &rdata;
	} else {
		op = MDB_SET;
		xdata = NULL;
		flags |= MDB_NODUPDATA;
	}
	rc = mdb_cursor_set(&mc, key, xdata, op, &exact);
	if (likely(rc == 0)) {
		/* let mdb_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_flags |= C_UNTRACK;
		mc.mc_next = txn->mt_cursors[dbi];
		txn->mt_cursors[dbi] = &mc;
		rc = mdb_cursor_del(&mc, flags);
		txn->mt_cursors[dbi] = mc.mc_next;
	}
	return rc;
}

/** Split a page and insert a new node.
 * @param[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.
 * @param[in] newkey The key for the newly inserted node.
 * @param[in] newdata The data for the newly inserted node.
 * @param[in] newpgno The page number, if the new node is a branch node.
 * @param[in] nflags The #NODE_ADD_FLAGS for the new node.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata, pgno_t newpgno,
	unsigned nflags)
{
	unsigned flags;
	int		 rc = MDB_SUCCESS, new_root = 0, did_split = 0;
	indx_t		 newindx;
	pgno_t		 pgno = 0;
	int	 i, j, split_indx, nkeys, pmax;
	MDB_env 	*env = mc->mc_txn->mt_env;
	MDB_node	*node;
	MDB_val	 sepkey, rkey, xdata, *rdata = &xdata;
	MDB_page	*copy = NULL;
	MDB_page	*mp, *rp, *pp;
	int ptop;
	MDB_cursor	mn;
	DKBUF;

	mp = mc->mc_pg[mc->mc_top];
	newindx = mc->mc_ki[mc->mc_top];
	nkeys = NUMKEYS(mp);

	mdb_debug("-----> splitting %s page %zu 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 = mdb_page_new(mc, mp->mp_flags, 1, &rp)))
		return rc;
	rp->mp_ksize = mp->mp_ksize;
	mdb_debug("new right sibling: page %zu", rp->mp_pgno);

	/* Usually when splitting the root page, the cursor
	 * height is 1. But when called from mdb_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 = mdb_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;
		mdb_debug("root split! new root = %zu", pp->mp_pgno);
		new_root = mc->mc_db->md_depth++;

		/* Add left (implicit) pointer. */
		if (unlikely((rc = mdb_node_add(mc, 0, NULL, NULL, mp->mp_pgno, 0)) != MDB_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;
		mdb_debug("parent branch page is %zu", mc->mc_pg[ptop]->mp_pgno);
	}

	mdb_cursor_copy(mc, &mn);
	mn.mc_xcursor = NULL;
	mn.mc_pg[mn.mc_top] = rp;
	mn.mc_ki[ptop] = mc->mc_ki[ptop]+1;

	if (nflags & MDB_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);
			mp->mp_lower -= lsize;
			rp->mp_lower += lsize;
			mp->mp_upper += rsize - lsize;
			rp->mp_upper -= rsize - lsize;
			sepkey.mv_size = ksize;
			if (newindx == split_indx) {
				sepkey.mv_data = newkey->mv_data;
			} else {
				sepkey.mv_data = split;
			}
			if (x<0) {
				ins = LEAF2KEY(mp, mc->mc_ki[mc->mc_top], ksize);
				memcpy(rp->mp_ptrs, split, rsize);
				sepkey.mv_data = rp->mp_ptrs;
				memmove(ins+ksize, ins, (split_indx - mc->mc_ki[mc->mc_top]) * ksize);
				memcpy(ins, newkey->mv_data, ksize);
				mp->mp_lower += sizeof(indx_t);
				mp->mp_upper -= ksize - sizeof(indx_t);
			} else {
				if (x)
					memcpy(rp->mp_ptrs, split, x * ksize);
				ins = LEAF2KEY(rp, x, ksize);
				memcpy(ins, newkey->mv_data, ksize);
				memcpy(ins+ksize, split + x * ksize, rsize - x * ksize);
				rp->mp_lower += sizeof(indx_t);
				rp->mp_upper -= ksize - sizeof(indx_t);
				mc->mc_ki[mc->mc_top] = x;
			}
		} else {
			int psize, nsize, k;
			/* Maximum free space in an empty page */
			pmax = env->me_psize - PAGEHDRSZ;
			if (IS_LEAF(mp))
				nsize = mdb_leaf_size(env, newkey, newdata);
			else
				nsize = mdb_branch_size(env, newkey);
			nsize = EVEN(nsize);

			/* grab a page to hold a temporary copy */
			copy = mdb_page_malloc(mc->mc_txn, 1);
			if (unlikely(copy == NULL)) {
				rc = ENOMEM;
				goto done;
			}
			copy->mp_pgno  = mp->mp_pgno;
			copy->mp_flags = mp->mp_flags;
			copy->mp_lower = (PAGEHDRSZ-PAGEBASE);
			copy->mp_upper = env->me_psize - PAGEBASE;

			/* prepare to insert */
			for (i=0, j=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 mdb_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.
			 */
			if (nkeys < 20 || nsize > pmax/16 || newindx >= nkeys) {
				/* Find split point */
				psize = 0;
				if (newindx <= split_indx || newindx >= nkeys) {
					i = 0; j = 1;
					k = newindx >= nkeys ? nkeys : split_indx+1+IS_LEAF(mp);
				} else {
					i = nkeys; j = -1;
					k = split_indx-1;
				}
				for (; i!=k; i+=j) {
					if (i == newindx) {
						psize += nsize;
						node = NULL;
					} else {
						node = (MDB_node *)((char *)mp + copy->mp_ptrs[i] + PAGEBASE);
						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-j) {
						split_indx = i + (j<0);
						break;
					}
				}
			}
			if (split_indx == newindx) {
				sepkey.mv_size = newkey->mv_size;
				sepkey.mv_data = newkey->mv_data;
			} else {
				node = (MDB_node *)((char *)mp + copy->mp_ptrs[split_indx] + PAGEBASE);
				sepkey.mv_size = node->mn_ksize;
				sepkey.mv_data = NODEKEY(node);
			}
		}
	}

	mdb_debug("separator is %d [%s]", split_indx, DKEY(&sepkey));

	/* Copy separator key to the parent.
	 */
	if (SIZELEFT(mn.mc_pg[ptop]) < mdb_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 = mdb_page_split(&mn, &sepkey, NULL, rp->mp_pgno, 0));
		if (unlikely(rc != MDB_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];
				mdb_cursor_sibling(mc, 0);
			}
		}
	} else {
		mn.mc_top--;
		rc = mdb_node_add(&mn, mn.mc_ki[ptop], &sepkey, NULL, rp->mp_pgno, 0);
		mn.mc_top++;
	}
	if (unlikely(rc != MDB_SUCCESS))
		goto done;
	if (nflags & MDB_APPEND) {
		mc->mc_pg[mc->mc_top] = rp;
		mc->mc_ki[mc->mc_top] = 0;
		rc = mdb_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;
		j = 0;
		do {
			if (i == newindx) {
				rkey.mv_data = newkey->mv_data;
				rkey.mv_size = newkey->mv_size;
				if (IS_LEAF(mp)) {
					rdata = newdata;
				} else
					pgno = newpgno;
				flags = nflags;
				/* Update index for the new key. */
				mc->mc_ki[mc->mc_top] = j;
			} else {
				node = (MDB_node *)((char *)mp + copy->mp_ptrs[i] + PAGEBASE);
				rkey.mv_data = NODEKEY(node);
				rkey.mv_size = node->mn_ksize;
				if (IS_LEAF(mp)) {
					xdata.mv_data = NODEDATA(node);
					xdata.mv_size = NODEDSZ(node);
					rdata = &xdata;
				} else
					pgno = NODEPGNO(node);
				flags = node->mn_flags;
			}

			if (!IS_LEAF(mp) && j == 0) {
				/* First branch index doesn't need key data. */
				rkey.mv_size = 0;
			}

			rc = mdb_node_add(mc, j, &rkey, rdata, pgno, flags);
			if (rc)
				goto done;
			if (i == nkeys) {
				i = 0;
				j = 0;
				mc->mc_pg[mc->mc_top] = copy;
			} else {
				i++;
				j++;
			}
		} 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 - PAGEBASE);

		/* 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 & MDB_RESERVE) {
			node = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
			if (!(node->mn_flags & F_BIGDATA))
				newdata->mv_data = 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 */
		MDB_cursor *m2, *m3;
		MDB_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 & MDB_SPLIT_REPLACE))
					m3->mc_ki[mc->mc_top]++;
				if (m3->mc_ki[mc->mc_top] >= nkeys) {
					m3->mc_pg[mc->mc_top] = rp;
					m3->mc_ki[mc->mc_top] -= 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 (m3->mc_xcursor && (m3->mc_xcursor->mx_cursor.mc_flags & C_INITIALIZED) &&
				IS_LEAF(mp)) {
				MDB_node *node = NODEPTR(m3->mc_pg[mc->mc_top], m3->mc_ki[mc->mc_top]);
				if ((node->mn_flags & (F_DUPDATA|F_SUBDATA)) == F_DUPDATA)
					m3->mc_xcursor->mx_cursor.mc_pg[0] = NODEDATA(node);
			}
		}
	}
	mdb_debug("mp left: %d, rp left: %d", SIZELEFT(mp), SIZELEFT(rp));

done:
	if (copy)					/* tmp page */
		mdb_page_free(env, copy);
	if (unlikely(rc))
		mc->mc_txn->mt_flags |= MDB_TXN_ERROR;
	return rc;
}

int
mdb_put(MDB_txn *txn, MDB_dbi dbi,
	MDB_val *key, MDB_val *data, unsigned flags)
{
	MDB_cursor mc;
	MDB_xcursor mx;
	int rc;

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

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

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

	if (unlikely(flags & ~(MDB_NOOVERWRITE|MDB_NODUPDATA|MDB_RESERVE|MDB_APPEND|MDB_APPENDDUP)))
		return EINVAL;

	if (unlikely(txn->mt_flags & (MDB_TXN_RDONLY|MDB_TXN_BLOCKED)))
		return (txn->mt_flags & MDB_TXN_RDONLY) ? EACCES : MDB_BAD_TXN;

	mdb_cursor_init(&mc, txn, dbi, &mx);
	mc.mc_next = txn->mt_cursors[dbi];
	txn->mt_cursors[dbi] = &mc;
	rc = mdb_cursor_put(&mc, key, data, flags);
	txn->mt_cursors[dbi] = mc.mc_next;
	return rc;
}

#ifndef MDB_WBUF
#define MDB_WBUF	(1024*1024)
#endif

	/** State needed for a compacting copy. */
typedef struct mdb_copy {
	pthread_mutex_t mc_mutex;
	pthread_cond_t mc_cond;
	char *mc_wbuf[2];
	char *mc_over[2];
	MDB_env *mc_env;
	MDB_txn *mc_txn;
	int mc_wlen[2];
	int mc_olen[2];
	pgno_t mc_next_pgno;
	HANDLE mc_fd;
	int mc_status;
	volatile int mc_new;
	int mc_toggle;

} mdb_copy;

	/** Dedicated writer thread for compacting copy. */
static void* __cold
mdb_env_copythr(void *arg)
{
	mdb_copy *my = arg;
	char *ptr;
	int toggle = 0, wsize, rc = 0;
	int len;

	pthread_mutex_lock(&my->mc_mutex);
	my->mc_new = 0;
	pthread_cond_signal(&my->mc_cond);
	for(;;) {
		while (!my->mc_new)
			pthread_cond_wait(&my->mc_cond, &my->mc_mutex);
		if (my->mc_new < 0) {
			my->mc_new = 0;
			break;
		}
		my->mc_new = 0;
		wsize = my->mc_wlen[toggle];
		ptr = my->mc_wbuf[toggle];
again:
		while (wsize > 0) {
			len = write(my->mc_fd, ptr, wsize);
			if (len < 0) {
				rc = errno;
				break;
			} else if (len > 0) {
				rc = MDB_SUCCESS;
				ptr += len;
				wsize -= len;
				continue;
			} else {
				rc = EIO;
				break;
			}
		}
		if (rc) {
			my->mc_status = rc;
			break;
		}
		/* 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;
		pthread_cond_signal(&my->mc_cond);
	}
	pthread_cond_signal(&my->mc_cond);
	pthread_mutex_unlock(&my->mc_mutex);
	return (void*)0;
}

	/** Tell the writer thread there's a buffer ready to write */
static int __cold
mdb_env_cthr_toggle(mdb_copy *my, int st)
{
	int toggle = my->mc_toggle ^ 1;
	pthread_mutex_lock(&my->mc_mutex);
	if (my->mc_status) {
		pthread_mutex_unlock(&my->mc_mutex);
		return my->mc_status;
	}
	while (my->mc_new == 1)
		pthread_cond_wait(&my->mc_cond, &my->mc_mutex);
	my->mc_new = st;
	my->mc_toggle = toggle;
	pthread_cond_signal(&my->mc_cond);
	pthread_mutex_unlock(&my->mc_mutex);
	return 0;
}

	/** Depth-first tree traversal for compacting copy. */
static int __cold
mdb_env_cwalk(mdb_copy *my, pgno_t *pg, int flags)
{
	MDB_cursor mc;
	MDB_txn *txn = my->mc_txn;
	MDB_node *ni;
	MDB_page *mo, *mp, *leaf;
	char *buf, *ptr;
	int rc, toggle;
	unsigned i;

	/* Empty DB, nothing to do */
	if (*pg == P_INVALID)
		return MDB_SUCCESS;

	mc.mc_snum = 1;
	mc.mc_top = 0;
	mc.mc_txn = txn;

	rc = mdb_page_get(my->mc_txn, *pg, &mc.mc_pg[0], NULL);
	if (rc)
		return rc;
	rc = mdb_page_search_root(&mc, NULL, MDB_PS_FIRST);
	if (rc)
		return rc;

	/* Make cursor pages writable */
	buf = ptr = malloc(my->mc_env->me_psize * mc.mc_snum);
	if (buf == NULL)
		return ENOMEM;

	for (i=0; i<mc.mc_top; i++) {
		mdb_page_copy((MDB_page *)ptr, mc.mc_pg[i], my->mc_env->me_psize);
		mc.mc_pg[i] = (MDB_page *)ptr;
		ptr += my->mc_env->me_psize;
	}

	/* This is writable space for a leaf page. Usually not needed. */
	leaf = (MDB_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) {
						MDB_page *omp;
						pgno_t pg;

						/* Need writable leaf */
						if (mp != leaf) {
							mc.mc_pg[mc.mc_top] = leaf;
							mdb_page_copy(leaf, mp, my->mc_env->me_psize);
							mp = leaf;
							ni = NODEPTR(mp, i);
						}

						memcpy(&pg, NODEDATA(ni), sizeof(pg));
						rc = mdb_page_get(txn, pg, &omp, NULL);
						if (rc)
							goto done;
						if (my->mc_wlen[toggle] >= MDB_WBUF) {
							rc = mdb_env_cthr_toggle(my, 1);
							if (rc)
								goto done;
							toggle = my->mc_toggle;
						}
						mo = (MDB_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] = my->mc_env->me_psize * (omp->mp_pages - 1);
							my->mc_over[toggle] = (char *)omp + my->mc_env->me_psize;
							rc = mdb_env_cthr_toggle(my, 1);
							if (rc)
								goto done;
							toggle = my->mc_toggle;
						}
						memcpy(NODEDATA(ni), &mo->mp_pgno, sizeof(pgno_t));
					} else if (ni->mn_flags & F_SUBDATA) {
						MDB_db db;

						/* Need writable leaf */
						if (mp != leaf) {
							mc.mc_pg[mc.mc_top] = leaf;
							mdb_page_copy(leaf, mp, my->mc_env->me_psize);
							mp = leaf;
							ni = NODEPTR(mp, i);
						}

						memcpy(&db, NODEDATA(ni), sizeof(db));
						my->mc_toggle = toggle;
						rc = mdb_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 pg;
again:
				ni = NODEPTR(mp, mc.mc_ki[mc.mc_top]);
				pg = NODEPGNO(ni);
				rc = mdb_page_get(txn, pg, &mp, NULL);
				if (rc)
					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.
					 */
					mdb_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] >= MDB_WBUF) {
			rc = mdb_env_cthr_toggle(my, 1);
			if (rc)
				goto done;
			toggle = my->mc_toggle;
		}
		mo = (MDB_page *)(my->mc_wbuf[toggle] + my->mc_wlen[toggle]);
		mdb_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);
			mdb_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
mdb_env_copyfd1(MDB_env *env, HANDLE fd)
{
	MDB_meta *mm;
	MDB_page *mp;
	mdb_copy my;
	MDB_txn *txn = NULL;
	pthread_t thr;
	int rc;

	pthread_mutex_init(&my.mc_mutex, NULL);
	pthread_cond_init(&my.mc_cond, NULL);
	rc = posix_memalign((void **)&my.mc_wbuf[0], env->me_os_psize, MDB_WBUF*2);
	if (rc)
		return rc;
	memset(my.mc_wbuf[0], 0, MDB_WBUF*2);
	my.mc_wbuf[1] = my.mc_wbuf[0] + MDB_WBUF;
	my.mc_wlen[0] = 0;
	my.mc_wlen[1] = 0;
	my.mc_olen[0] = 0;
	my.mc_olen[1] = 0;
	my.mc_next_pgno = NUM_METAS;
	my.mc_status = 0;
	my.mc_new = 1;
	my.mc_toggle = 0;
	my.mc_env = env;
	my.mc_fd = fd;
	rc = pthread_create(&thr, NULL, mdb_env_copythr, &my);
	assert(rc == 0);

	rc = mdb_txn_begin(env, NULL, MDB_RDONLY, &txn);
	if (rc)
		return rc;

	mp = (MDB_page *)my.mc_wbuf[0];
	memset(mp, 0, NUM_METAS * env->me_psize);
	mp->mp_pgno = 0;
	mp->mp_flags = P_META;
	mm = (MDB_meta *)PAGEDATA(mp);
	mdb_env_init_meta0(env, mm);
	mm->mm_address = METAPAGE_1(env)->mm_address;

	mp = (MDB_page *)(my.mc_wbuf[0] + env->me_psize);
	mp->mp_pgno = 1;
	mp->mp_flags = P_META;
	*(MDB_meta *)PAGEDATA(mp) = *mm;
	mm = (MDB_meta *)PAGEDATA(mp);

	/* Count the number of free pages, subtract from lastpg to find
	 * number of active pages
	 */
	{
		MDB_ID freecount = 0;
		MDB_cursor mc;
		MDB_val key, data;
		mdb_cursor_init(&mc, txn, FREE_DBI, NULL);
		while ((rc = mdb_cursor_get(&mc, &key, &data, MDB_NEXT)) == 0)
			freecount += *(MDB_ID *)data.mv_data;
		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;

		/* Set metapage 1 */
		mm->mm_last_pg = txn->mt_next_pgno - freecount - 1;
		mm->mm_dbs[MAIN_DBI] = txn->mt_dbs[MAIN_DBI];
		if (mm->mm_last_pg > NUM_METAS-1) {
			mm->mm_dbs[MAIN_DBI].md_root = mm->mm_last_pg;
			mm->mm_txnid = 1;
		} else {
			mm->mm_dbs[MAIN_DBI].md_root = P_INVALID;
		}
	}
	my.mc_wlen[0] = env->me_psize * NUM_METAS;
	my.mc_txn = txn;
	pthread_mutex_lock(&my.mc_mutex);
	while(my.mc_new)
		pthread_cond_wait(&my.mc_cond, &my.mc_mutex);
	pthread_mutex_unlock(&my.mc_mutex);
	rc = mdb_env_cwalk(&my, &txn->mt_dbs[MAIN_DBI].md_root, 0);
	if (rc == MDB_SUCCESS && my.mc_wlen[my.mc_toggle])
		rc = mdb_env_cthr_toggle(&my, 1);
	mdb_env_cthr_toggle(&my, -1);
	pthread_mutex_lock(&my.mc_mutex);
	while(my.mc_new)
		pthread_cond_wait(&my.mc_cond, &my.mc_mutex);
	pthread_mutex_unlock(&my.mc_mutex);
	pthread_join(thr, NULL);

	mdb_txn_abort(txn);
	pthread_cond_destroy(&my.mc_cond);
	pthread_mutex_destroy(&my.mc_mutex);
	free(my.mc_wbuf[0]);
	return rc;
}

	/** Copy environment as-is. */
static int __cold
mdb_env_copyfd0(MDB_env *env, HANDLE fd)
{
	MDB_txn *txn = NULL;
	pthread_mutex_t *wmutex = NULL;
	int rc;
	size_t wsize;
	char *ptr;
	ssize_t len;
	size_t w2;

	/* Do the lock/unlock of the reader mutex before starting the
	 * write txn.  Otherwise other read txns could block writers.
	 */
	rc = mdb_txn_begin(env, NULL, MDB_RDONLY, &txn);
	if (rc)
		return rc;

	/* We must start the actual read txn after blocking writers */
	rc = mdb_txn_end(txn, MDB_END_RESET_TMP);
	if (rc)
		return rc;

	/* Temporarily block writers until we snapshot the meta pages */
	wmutex = MDB_MUTEX(env, w);
	rc = mdb_mutex_lock(env, wmutex);
	if (unlikely(rc))
		goto leave;

	rc = mdb_txn_renew0(txn, MDB_RDONLY);
	if (rc) {
		mdb_mutex_unlock(env, wmutex);
		goto leave;
	}

	wsize = env->me_psize * NUM_METAS;
	ptr = env->me_map;
	w2 = wsize;
	while (w2 > 0) {
		len = write(fd, ptr, w2);
		if (len < 0) {
			rc = errno;
			break;
		} else if (len > 0) {
			rc = MDB_SUCCESS;
			ptr += len;
			w2 -= len;
			continue;
		} else {
			/* Non-blocking or async handles are not supported */
			rc = EIO;
			break;
		}
	}
	mdb_mutex_unlock(env, wmutex);

	if (rc)
		goto leave;

	w2 = txn->mt_next_pgno * env->me_psize;
	{
		size_t fsize = 0;
		if ((rc = mdb_fsize(env->me_fd, &fsize)))
			goto leave;
		if (w2 > fsize)
			w2 = fsize;
	}
	wsize = w2 - wsize;
	while (wsize > 0) {
		if (wsize > MAX_WRITE)
			w2 = MAX_WRITE;
		else
			w2 = wsize;
		len = write(fd, ptr, w2);
		if (len < 0 ) {
			rc = errno;
			break;
		} else if (len > 0) {
			rc = MDB_SUCCESS;
			ptr += len;
			wsize -= len;
			continue;
		} else {
			rc = EIO;
			break;
		}
	}

leave:
	mdb_txn_abort(txn);
	return rc;
}

int __cold
mdb_env_copyfd2(MDB_env *env, HANDLE fd, unsigned flags)
{
	if (flags & MDB_CP_COMPACT)
		return mdb_env_copyfd1(env, fd);
	else
		return mdb_env_copyfd0(env, fd);
}

int __cold
mdb_env_copyfd(MDB_env *env, HANDLE fd)
{
	return mdb_env_copyfd2(env, fd, 0);
}

int __cold
mdb_env_copy2(MDB_env *env, const char *path, unsigned flags)
{
	int rc, len;
	char *lpath;
	HANDLE newfd = INVALID_HANDLE_VALUE;

	if (env->me_flags & MDB_NOSUBDIR) {
		lpath = (char *)path;
	} else {
		len = strlen(path);
		len += sizeof(DATANAME);
		lpath = malloc(len);
		if (!lpath)
			return ENOMEM;
		sprintf(lpath, "%s" 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.
	 */
	newfd = open(lpath, O_WRONLY|O_CREAT|O_EXCL, 0666);
	if (newfd == INVALID_HANDLE_VALUE) {
		rc = errno;
		goto leave;
	}

	if (env->me_psize >= env->me_os_psize) {
#ifdef O_DIRECT
	/* 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
#ifdef F_NOCACHE	/* __APPLE__ */
	rc = fcntl(newfd, F_NOCACHE, 1);
	if (rc) {
		rc = errno;
		goto leave;
	}
#endif
	}

	rc = mdb_env_copyfd2(env, newfd, flags);

leave:
	if (!(env->me_flags & MDB_NOSUBDIR))
		free(lpath);
	if (newfd != INVALID_HANDLE_VALUE)
		if (close(newfd) < 0 && rc == MDB_SUCCESS)
			rc = errno;

	return rc;
}

int __cold
mdb_env_copy(MDB_env *env, const char *path)
{
	return mdb_env_copy2(env, path, 0);
}

int __cold
mdb_env_set_flags(MDB_env *env, unsigned flags, int onoff)
{
	if (unlikely(flags & ~CHANGEABLE))
		return EINVAL;

	pthread_mutex_t *mutex = MDB_MUTEX(env, w);
	int rc = mdb_mutex_lock(env, mutex);
	if (unlikely(rc))
		return rc;

	if (onoff)
		flags = env->me_flags | flags;
	else
		flags = env->me_flags & ~flags;

#if MDB_LIFORECLAIM
	/* LY: don't allow LIFO with just NOMETASYNC */
	if ((flags & (MDB_NOMETASYNC | MDB_LIFORECLAIM | MDB_NOSYNC))
			== (MDB_NOMETASYNC | MDB_LIFORECLAIM))
		return EINVAL;
#endif /* MDB_LIFORECLAIM */
	env->me_flags = flags;

	mdb_mutex_unlock(env, mutex);
	return MDB_SUCCESS;
}

int __cold
mdb_env_get_flags(MDB_env *env, unsigned *arg)
{
	if (unlikely(!env || !arg))
		return EINVAL;

	*arg = env->me_flags & (CHANGEABLE|CHANGELESS);
	return MDB_SUCCESS;
}

int __cold
mdb_env_set_userctx(MDB_env *env, void *ctx)
{
	if (unlikely(!env))
		return EINVAL;
	env->me_userctx = ctx;
	return MDB_SUCCESS;
}

void * __cold
mdb_env_get_userctx(MDB_env *env)
{
	return env ? env->me_userctx : NULL;
}

int __cold
mdb_env_set_assert(MDB_env *env, MDB_assert_func *func)
{
	if (unlikely(!env))
		return EINVAL;
#if MDB_DEBUG
	env->me_assert_func = func;
	return MDB_SUCCESS;
#else
	(void) func;
	return ENOSYS;
#endif
}

int __cold
mdb_env_get_path(MDB_env *env, const char **arg)
{
	if (unlikely(!env || !arg))
		return EINVAL;

	*arg = env->me_path;
	return MDB_SUCCESS;
}

int __cold
mdb_env_get_fd(MDB_env *env, mdb_filehandle_t *arg)
{
	if (unlikely(!env || !arg))
		return EINVAL;

	*arg = env->me_fd;
	return MDB_SUCCESS;
}

/** Common code for #mdb_stat() and #mdb_env_stat().
 * @param[in] env the environment to operate in.
 * @param[in] db the #MDB_db record containing the stats to return.
 * @param[out] arg the address of an #MDB_stat structure to receive the stats.
 * @return 0, this function always succeeds.
 */
static int __cold
mdb_stat0(MDB_env *env, MDB_db *db, MDB_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 MDB_SUCCESS;
}

#if ! MDBX_MODE_ENABLED
static
#endif /* ! MDBX_MODE_ENABLED */
int __cold
mdbx_env_stat(MDB_env *env, MDBX_stat *arg, size_t bytes)
{
	MDB_meta *meta;

	if (unlikely(env == NULL || arg == NULL))
		return EINVAL;
	if (unlikely(bytes != sizeof(MDBX_stat)))
		return EINVAL;

	meta = mdb_meta_head_r(env);
	return mdb_stat0(env, &meta->mm_dbs[MAIN_DBI], &arg->base);
}

int __cold
mdb_env_stat(MDB_env *env, MDB_stat *arg)
{
	return mdbx_env_stat(env, (MDBX_stat *) arg, sizeof(MDB_stat));
}

#if ! MDBX_MODE_ENABLED
static
#endif /* ! MDBX_MODE_ENABLED */
int __cold
mdbx_env_info(MDB_env *env, MDBX_envinfo *arg, size_t bytes)
{
	MDB_meta *meta;

	if (unlikely(env == NULL || arg == NULL))
		return EINVAL;

	if (bytes == sizeof(MDB_envinfo)) {
		do {
			meta = mdb_meta_head_r(env);
			arg->base.me_last_txnid = meta->mm_txnid;
			arg->base.me_last_pgno = meta->mm_last_pg;
			arg->base.me_mapaddr = meta->mm_address;
			arg->base.me_mapsize = env->me_mapsize;
			arg->base.me_maxreaders = env->me_maxreaders;
			arg->base.me_numreaders = env->me_txns->mti_numreaders;
		} while (unlikely( arg->base.me_last_txnid != env->me_txns->mti_txnid));
#if MDBX_MODE_ENABLED
	} else if (bytes == sizeof(MDBX_envinfo)) {
		MDB_meta *m1, *m2;
		MDB_reader *r;
		unsigned i;

		m1 = METAPAGE_1(env);
		m2 = METAPAGE_2(env);

		do {
			meta = mdb_meta_head_r(env);
			arg->base.me_last_txnid = meta->mm_txnid;
			arg->base.me_last_pgno = meta->mm_last_pg;
			arg->me_meta1_txnid = m1->mm_txnid;
			arg->me_meta1_sign = m1->mm_datasync_sign;
			arg->me_meta2_txnid = m2->mm_txnid;
			arg->me_meta2_sign = m2->mm_datasync_sign;
		} while (unlikely( arg->base.me_last_txnid != env->me_txns->mti_txnid
				|| arg->me_meta1_sign != m1->mm_datasync_sign
				|| arg->me_meta2_sign != m2->mm_datasync_sign ));

		arg->base.me_mapaddr = meta->mm_address;
		arg->base.me_mapsize = env->me_mapsize;
		arg->base.me_maxreaders = env->me_maxreaders;
		arg->base.me_numreaders = env->me_txns->mti_numreaders;
		arg->me_tail_txnid = 0;

		r = env->me_txns->mti_readers;
		arg->me_tail_txnid = arg->base.me_last_txnid;
		for (i = 0; i < arg->base.me_numreaders; ++i ) {
			if (r[i].mr_pid) {
				txnid_t mr = r[i].mr_txnid;
				if (arg->me_tail_txnid > mr)
					arg->me_tail_txnid = mr;
			}
		}
#endif /* MDBX_MODE_ENABLED */
	} else {
		return EINVAL;
	}

	return MDB_SUCCESS;
}

int __cold
mdb_env_info(MDB_env *env, MDB_envinfo *arg)
{
	return mdbx_env_info(env, (MDBX_envinfo*) arg, sizeof(MDB_envinfo));
}

/** Set the default comparison functions for a database.
 * Called immediately after a database is opened to set the defaults.
 * The user can then override them with #mdb_set_compare() or
 * #mdb_set_dupsort().
 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
 * @param[in] dbi A database handle returned by #mdb_dbi_open()
 */
static void
mdb_default_cmp(MDB_txn *txn, MDB_dbi dbi)
{
	unsigned f = txn->mt_dbs[dbi].md_flags;

	txn->mt_dbxs[dbi].md_cmp =
		(f & MDB_REVERSEKEY) ? mdb_cmp_memnr :
		(f & MDB_INTEGERKEY) ? mdb_cmp_int_a2 : mdb_cmp_memn;

	txn->mt_dbxs[dbi].md_dcmp =
		!(f & MDB_DUPSORT) ? 0 :
		((f & MDB_INTEGERDUP) ? mdb_cmp_int_ua :
		((f & MDB_REVERSEDUP) ? mdb_cmp_memnr : mdb_cmp_memn));
}

int mdb_dbi_open(MDB_txn *txn, const char *name, unsigned flags, MDB_dbi *dbi)
{
	MDB_val key, data;
	MDB_dbi i;
	MDB_cursor mc;
	MDB_db dummy;
	int rc, dbflag, exact;
	unsigned unused = 0, seq;
	char *namedup;
	size_t len;

	if (unlikely(!txn || !dbi))
		return EINVAL;

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

	if (unlikely(flags & ~VALID_FLAGS))
		return EINVAL;

	if (unlikely(txn->mt_flags & MDB_TXN_BLOCKED))
		return MDB_BAD_TXN;

	/* main DB? */
	if (!name) {
		*dbi = MAIN_DBI;
		if (flags & PERSISTENT_FLAGS) {
			uint16_t f2 = flags & PERSISTENT_FLAGS;
			/* make sure flag changes get committed */
			if ((txn->mt_dbs[MAIN_DBI].md_flags | f2) != txn->mt_dbs[MAIN_DBI].md_flags) {
				txn->mt_dbs[MAIN_DBI].md_flags |= f2;
				txn->mt_flags |= MDB_TXN_DIRTY;
			}
		}
		mdb_default_cmp(txn, MAIN_DBI);
		return MDB_SUCCESS;
	}

	if (txn->mt_dbxs[MAIN_DBI].md_cmp == NULL) {
		mdb_default_cmp(txn, MAIN_DBI);
	}

	/* Is the DB already open? */
	len = strlen(name);
	for (i=CORE_DBS; i<txn->mt_numdbs; i++) {
		if (!txn->mt_dbxs[i].md_name.mv_size) {
			/* Remember this free slot */
			if (!unused) unused = i;
			continue;
		}
		if (len == txn->mt_dbxs[i].md_name.mv_size &&
			!strncmp(name, txn->mt_dbxs[i].md_name.mv_data, len)) {
			*dbi = i;
			return MDB_SUCCESS;
		}
	}

	/* If no free slot and max hit, fail */
	if (!unused && unlikely(txn->mt_numdbs >= txn->mt_env->me_maxdbs))
		return MDB_DBS_FULL;

	/* Cannot mix named databases with some mainDB flags */
	if (unlikely(txn->mt_dbs[MAIN_DBI].md_flags & (MDB_DUPSORT|MDB_INTEGERKEY)))
		return (flags & MDB_CREATE) ? MDB_INCOMPATIBLE : MDB_NOTFOUND;

	/* Find the DB info */
	dbflag = DB_NEW|DB_VALID|DB_USRVALID;
	exact = 0;
	key.mv_size = len;
	key.mv_data = (void *)name;
	mdb_cursor_init(&mc, txn, MAIN_DBI, NULL);
	rc = mdb_cursor_set(&mc, &key, &data, MDB_SET, &exact);
	if (likely(rc == MDB_SUCCESS)) {
		/* make sure this is actually a DB */
		MDB_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 MDB_INCOMPATIBLE;
	} else if (! (rc == MDB_NOTFOUND && (flags & MDB_CREATE))) {
		return rc;
	}

	/* Done here so we cannot fail after creating a new DB */
	if (unlikely((namedup = strdup(name)) == NULL))
		return ENOMEM;

	if (unlikely(rc)) {
		/* MDB_NOTFOUND and MDB_CREATE: Create new DB */
		data.mv_size = sizeof(MDB_db);
		data.mv_data = &dummy;
		memset(&dummy, 0, sizeof(dummy));
		dummy.md_root = P_INVALID;
		dummy.md_flags = flags & PERSISTENT_FLAGS;
		rc = mdb_cursor_put(&mc, &key, &data, F_SUBDATA);
		dbflag |= DB_DIRTY;
	}

	if (unlikely(rc)) {
		free(namedup);
	} else {
		/* Got info, register DBI in this txn */
		unsigned slot = unused ? unused : txn->mt_numdbs;
		txn->mt_dbxs[slot].md_name.mv_data = namedup;
		txn->mt_dbxs[slot].md_name.mv_size = len;
		txn->mt_dbxs[slot].md_rel = NULL;
		txn->mt_dbflags[slot] = dbflag;
		/* txn-> and env-> are the same in read txns, use
		 * tmp variable to avoid undefined assignment
		 */
		seq = ++txn->mt_env->me_dbiseqs[slot];
		txn->mt_dbiseqs[slot] = seq;

		memcpy(&txn->mt_dbs[slot], data.mv_data, sizeof(MDB_db));
		*dbi = slot;
		mdb_default_cmp(txn, slot);
		if (!unused) {
			txn->mt_numdbs++;
		}
	}

	return rc;
}

#if ! MDBX_MODE_ENABLED
static
#endif
int __cold
mdbx_stat(MDB_txn *txn, MDB_dbi dbi, MDBX_stat *arg, size_t bytes)
{
	if (unlikely(!arg || !txn))
		return EINVAL;

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

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

	if (unlikely(bytes != sizeof(MDBX_stat)))
		return EINVAL;

	if (unlikely(txn->mt_flags & MDB_TXN_BLOCKED))
		return MDB_BAD_TXN;

	if (txn->mt_dbflags[dbi] & DB_STALE) {
		MDB_cursor mc;
		MDB_xcursor mx;
		/* Stale, must read the DB's root. cursor_init does it for us. */
		mdb_cursor_init(&mc, txn, dbi, &mx);
	}
	return mdb_stat0(txn->mt_env, &txn->mt_dbs[dbi], &arg->base);
}

int __cold
mdb_stat(MDB_txn *txn, MDB_dbi dbi, MDB_stat *arg)
{
	return mdbx_stat(txn, dbi, (MDBX_stat*) arg, sizeof(MDB_stat));
}

void mdb_dbi_close(MDB_env *env, MDB_dbi dbi)
{
	char *ptr;
	if (dbi < CORE_DBS || dbi >= env->me_maxdbs)
		return;
	ptr = env->me_dbxs[dbi].md_name.mv_data;
	/* If there was no name, this was already closed */
	if (ptr) {
		env->me_dbxs[dbi].md_name.mv_data = NULL;
		env->me_dbxs[dbi].md_name.mv_size = 0;
		env->me_dbflags[dbi] = 0;
		env->me_dbiseqs[dbi]++;
		free(ptr);
	}
}

int mdb_dbi_flags(MDB_txn *txn, MDB_dbi dbi, unsigned *flags)
{
	if (unlikely(!txn || !flags))
		return EINVAL;

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

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

	*flags = txn->mt_dbs[dbi].md_flags & PERSISTENT_FLAGS;
	return MDB_SUCCESS;
}

/** Add all the DB's pages to the free list.
 * @param[in] mc Cursor on the DB to free.
 * @param[in] subs non-Zero to check for sub-DBs in this DB.
 * @return 0 on success, non-zero on failure.
 */
static int
mdb_drop0(MDB_cursor *mc, int subs)
{
	int rc;

	rc = mdb_page_search(mc, NULL, MDB_PS_FIRST);
	if (likely(rc == MDB_SUCCESS)) {
		MDB_txn *txn = mc->mc_txn;
		MDB_node *ni;
		MDB_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))
			mdb_cursor_pop(mc);

		mdb_cursor_copy(mc, &mx);
		while (mc->mc_snum > 0) {
			MDB_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) {
						MDB_page *omp;
						pgno_t pg;
						memcpy(&pg, NODEDATA(ni), sizeof(pg));
						rc = mdb_page_get(txn, pg, &omp, NULL);
						if (unlikely(rc))
							goto done;
						mdb_cassert(mc, IS_OVERFLOW(omp));
						rc = mdb_midl_append_range(&txn->mt_free_pgs,
							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)) {
						mdb_xcursor_init1(mc, ni);
						rc = mdb_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 = mdb_midl_need(&txn->mt_free_pgs, n)) != 0))
					goto done;
				for (i=0; i<n; i++) {
					pgno_t pg;
					ni = NODEPTR(mp, i);
					pg = NODEPGNO(ni);
					/* free it */
					mdb_midl_xappend(txn->mt_free_pgs, pg);
				}
			}
			if (!mc->mc_top)
				break;
			mc->mc_ki[mc->mc_top] = i;
			rc = mdb_cursor_sibling(mc, 1);
			if (rc) {
				if (unlikely(rc != MDB_NOTFOUND))
					goto done;
				/* no more siblings, go back to beginning
				 * of previous level.
				 */
pop:
				mdb_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 = mdb_midl_append(&txn->mt_free_pgs, mc->mc_db->md_root);
done:
		if (unlikely(rc))
			txn->mt_flags |= MDB_TXN_ERROR;
	} else if (rc == MDB_NOTFOUND) {
		rc = MDB_SUCCESS;
	}
	mc->mc_flags &= ~C_INITIALIZED;
	return rc;
}

int mdb_drop(MDB_txn *txn, MDB_dbi dbi, int del)
{
	MDB_cursor *mc, *m2;
	int rc;

	if (unlikely(1 < (unsigned) del || !txn))
		return EINVAL;

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

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

	if (unlikely(TXN_DBI_CHANGED(txn, dbi)))
		return MDB_BAD_DBI;

	if (unlikely(F_ISSET(txn->mt_flags, MDB_TXN_RDONLY)))
		return EACCES;

	rc = mdb_cursor_open(txn, dbi, &mc);
	if (unlikely(rc))
		return rc;

	rc = mdb_drop0(mc, mc->mc_db->md_flags & MDB_DUPSORT);
	/* Invalidate the dropped DB's cursors */
	for (m2 = txn->mt_cursors[dbi]; m2; m2 = m2->mc_next)
		m2->mc_flags &= ~(C_INITIALIZED|C_EOF);
	if (unlikely(rc))
		goto leave;

	/* Can't delete the main DB */
	if (del && dbi >= CORE_DBS) {
		rc = mdb_del0(txn, MAIN_DBI, &mc->mc_dbx->md_name, NULL, F_SUBDATA);
		if (likely(!rc)) {
			txn->mt_dbflags[dbi] = DB_STALE;
			mdb_dbi_close(txn->mt_env, dbi);
		} else {
			txn->mt_flags |= MDB_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_flags |= MDB_TXN_DIRTY;
	}
leave:
	mdb_cursor_close(mc);
	return rc;
}

int mdb_set_compare(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
{
	if (unlikely(!txn))
		return EINVAL;

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

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

	txn->mt_dbxs[dbi].md_cmp = cmp;
	return MDB_SUCCESS;
}

int mdb_set_dupsort(MDB_txn *txn, MDB_dbi dbi, MDB_cmp_func *cmp)
{
	if (unlikely(!txn))
		return EINVAL;

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

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

	txn->mt_dbxs[dbi].md_dcmp = cmp;
	return MDB_SUCCESS;
}

int mdb_set_relfunc(MDB_txn *txn, MDB_dbi dbi, MDB_rel_func *rel)
{
	if (unlikely(!txn))
		return EINVAL;

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

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

	txn->mt_dbxs[dbi].md_rel = rel;
	return MDB_SUCCESS;
}

int mdb_set_relctx(MDB_txn *txn, MDB_dbi dbi, void *ctx)
{
	if (unlikely(!txn))
		return EINVAL;

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

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

	txn->mt_dbxs[dbi].md_relctx = ctx;
	return MDB_SUCCESS;
}

int __cold
mdb_env_get_maxkeysize(MDB_env *env)
{
	if (!env || env->me_signature != MDBX_ME_SIGNATURE)
		return EINVAL;
	return ENV_MAXKEY(env);
}

int __cold
mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx)
{
	unsigned i, rdrs;
	MDB_reader *mr;
	char buf[64];
	int rc = 0, first = 1;

	if (unlikely(!env || !func))
		return -EINVAL;

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

	rdrs = env->me_txns->mti_numreaders;
	mr = env->me_txns->mti_readers;
	for (i=0; i<rdrs; i++) {
		if (mr[i].mr_pid) {
			txnid_t	txnid = mr[i].mr_txnid;
			if (txnid == ~(txnid_t)0)
				sprintf(buf, "%10d %zx -\n",
					(int) mr[i].mr_pid, (size_t) mr[i].mr_tid);
			else
				sprintf(buf, "%10d %zx %zu\n",
					(int) mr[i].mr_pid, (size_t) mr[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
mdb_pid_insert(pid_t *ids, pid_t pid)
{
	/* binary search of pid in list */
	unsigned base = 0;
	unsigned cursor = 1;
	int val = 0;
	unsigned n = ids[0];

	while( 0 < n ) {
		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
mdb_reader_check(MDB_env *env, int *dead)
{
	if (unlikely(!env || env->me_signature != MDBX_ME_SIGNATURE))
		return EINVAL;
	if (dead)
		*dead = 0;
	return mdb_reader_check0(env, 0, dead);
}

/** As #mdb_reader_check(). rlocked = <caller locked the reader mutex>. */
static int __cold
mdb_reader_check0(MDB_env *env, int rlocked, int *dead)
{
	pthread_mutex_t *rmutex = rlocked ? NULL : MDB_MUTEX(env, r);
	unsigned i, j, rdrs;
	MDB_reader *mr;
	pid_t *pids, pid;
	int rc = MDB_SUCCESS, count = 0;

	if (unlikely(env->me_pid != getpid())) {
		env->me_flags |= MDB_FATAL_ERROR;
		return MDB_PANIC;
	}

	rdrs = env->me_txns->mti_numreaders;
	pids = malloc((rdrs+1) * sizeof(pid_t));
	if (!pids)
		return ENOMEM;
	pids[0] = 0;
	mr = env->me_txns->mti_readers;
	for (i=0; i<rdrs; i++) {
		pid = mr[i].mr_pid;
		if (pid && pid != env->me_pid) {
			if (mdb_pid_insert(pids, pid) == 0) {
				if (!mdb_reader_pid(env, F_GETLK, pid)) {
					/* Stale reader found */
					j = i;
					if (rmutex) {
						if ((rc = pthread_mutex_lock(rmutex)) != 0) {
							if ((rc = mdb_mutex_failed(env, rmutex, rc)))
								break;
							rdrs = 0; /* the above checked all readers */
						} else {
							/* Recheck, a new process may have reused pid */
							if (mdb_reader_pid(env, F_GETLK, pid))
								j = rdrs;
						}
					}
					for (; j<rdrs; j++)
							if (mr[j].mr_pid == pid) {
								mdb_debug("clear stale reader pid %u txn %zd",
									(unsigned) pid, mr[j].mr_txnid);
								mr[j].mr_rthc = NULL;
								mdb_compiler_barrier();
								mr[j].mr_pid = 0;
								count++;
							}
					if (rmutex)
						mdb_mutex_unlock(env, rmutex);
				}
			}
		}
	}
	free(pids);
	if (dead)
		*dead = count;
	return rc;
}

static int __cold
mdb_mutex_failed(MDB_env *env, pthread_mutex_t *mutex, int rc)
{
#if MDB_USE_ROBUST
	if (unlikely(rc == EOWNERDEAD)) {
		int rlocked, rc2;

		/* We own the mutex. Clean up after dead previous owner. */
		rc = MDB_SUCCESS;
		rlocked = (mutex == MDB_MUTEX(env, r));
		if (!rlocked) {
			/* Keep mti_txnid updated, otherwise next writer can
			 * overwrite data which latest meta page refers to.
			 */
	#if 0
			/* LY: Hm, how this can happen, if the mti_txnid
			 * is updating only at the finish of a successful commit ? */

			MDB_meta *meta = mdb_env_meta_head(env);
			env->me_txns->mti_txnid = meta->mm_txnid;
	#endif
			/* env is hosed if the dead thread was ours */
			if (env->me_txn) {
				env->me_flags |= MDB_FATAL_ERROR;
				env->me_txn = NULL;
				rc = MDB_PANIC;
			}
		}
		mdb_debug("%cmutex owner died, %s", (rlocked ? 'r' : 'w'),
			(rc ? "this process' env is hosed" : "recovering"));
		rc2 = mdb_reader_check0(env, rlocked, NULL);
		if (rc2 == 0)
			rc2 = pthread_mutex_consistent(mutex);
		if (rc || (rc = rc2)) {
			mdb_debug("mutex recovery failed, %s", mdb_strerror(rc));
			pthread_mutex_unlock(mutex);
		}
	}
#endif /* MDB_USE_ROBUST */
	if (unlikely(rc)) {
		mdb_debug("lock mutex failed, %s", mdb_strerror(rc));
		if (rc != EDEADLK) {
			env->me_flags |= MDB_FATAL_ERROR;
			rc = MDB_PANIC;
		}
	}

	return rc;
}

static int mdb_mutex_lock(MDB_env *env, pthread_mutex_t *mutex) {
	int rc = pthread_mutex_lock(mutex);
	if (unlikely(rc))
		rc = mdb_mutex_failed(env, mutex, rc);
	return rc;
}

static void mdb_mutex_unlock(MDB_env *env, pthread_mutex_t *mutex) {
	int rc = pthread_mutex_unlock(mutex);
	mdb_assert(env, rc == 0);
	(void) env;
	(void) rc;
}

#if MDBX_MODE_ENABLED

void __cold
mdbx_env_set_oomfunc(MDB_env *env, MDB_oom_func *oomfunc)
{
	if (likely(env && env->me_signature == MDBX_ME_SIGNATURE))
		env->me_oom_func = oomfunc;
}

MDB_oom_func* __cold
mdbx_env_get_oomfunc(MDB_env *env)
{
	return likely(env && env->me_signature == MDBX_ME_SIGNATURE)
		? env->me_oom_func : NULL;
}

struct mdb_walk_ctx {
	MDB_txn *mw_txn;
	void *mw_user;
	MDB_pgvisitor_func *mw_visitor;
};

typedef struct mdb_walk_ctx mdb_walk_ctx_t;


/** Depth-first tree traversal. */
static int __cold
mdb_env_walk(mdb_walk_ctx_t *ctx, const char* dbi, pgno_t pg, int flags, int deep)
{
	MDB_page *mp;
	int rc, i, nkeys;
	unsigned header_size, unused_size, payload_size, align_bytes;
	const char* type;

	if (pg == P_INVALID)
		return MDB_CORRUPTED;

	rc = mdb_page_get(ctx->mw_txn, pg, &mp, NULL);
	if (rc)
		return rc;
	if (pg != mp->mp_p.p_pgno)
		return MDB_CORRUPTED;

	nkeys = NUMKEYS(mp);
	header_size = IS_LEAF2(mp) ? PAGEHDRSZ : PAGEBASE + 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 MDB_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 MDB_CORRUPTED;
	}

	for (align_bytes = i = 0; i < nkeys;
		 align_bytes += ((payload_size + align_bytes) & 1), i++) {
		MDB_node *node;

		if (IS_LEAF2(mp)) {
			/* LEAF2 pages have no mp_ptrs[] or node headers */
			payload_size += mp->mp_ksize;
			continue;
		}

		node = NODEPTR(mp, i);
		payload_size += NODESIZE + node->mn_ksize;

		if (IS_BRANCH(mp)) {
			rc = mdb_env_walk(ctx, dbi, NODEPGNO(node), flags, deep);
			if (rc)
				return rc;
			continue;
		}

		assert(IS_LEAF(mp));
		if (node->mn_ksize < 1)
			return MDB_CORRUPTED;
		if (node->mn_flags & F_BIGDATA) {
			MDB_page *omp;
			pgno_t *opg;
			size_t over_header, over_payload, over_unused;

			payload_size += sizeof(pgno_t);
			opg = NODEDATA(node);
			rc = mdb_page_get(ctx->mw_txn, *opg, &omp, NULL);
			if (rc)
				return rc;
			if (*opg != omp->mp_p.p_pgno)
				return MDB_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 MDB_CORRUPTED;

			over_header = PAGEHDRSZ;
			over_payload = NODEDSZ(node);
			over_unused = omp->mp_pages * ctx->mw_txn->mt_env->me_psize
					- 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) {
			MDB_db *db = NODEDATA(node);
			char* name = NULL;

			if (NODEDSZ(node) < 1)
				return MDB_CORRUPTED;
			if (! (node->mn_flags & F_DUPDATA)) {
				name = NODEKEY(node);
				int namelen = (char*) db - name;
				name = memcpy(alloca(namelen + 1), name, namelen);
				name[namelen] = 0;
			}
			rc = mdb_env_walk(ctx, (name && name[0]) ? name : dbi,
					db->md_root, node->mn_flags & F_DUPDATA, deep + 1);
			if (rc)
				return rc;
		}
	}

	return ctx->mw_visitor(mp->mp_p.p_pgno, 1, ctx->mw_user, dbi, type,
		nkeys, payload_size, header_size, unused_size + align_bytes);
}

int __cold
mdbx_env_pgwalk(MDB_txn *txn, MDB_pgvisitor_func* visitor, void* user)
{
	mdb_walk_ctx_t ctx;
	int rc;

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

	ctx.mw_txn = txn;
	ctx.mw_user = user;
	ctx.mw_visitor = visitor;

	rc = visitor(0, 2, user, "lmdb", "meta", 2, sizeof(MDB_meta)*2, PAGEHDRSZ*2,
				 (txn->mt_env->me_psize - sizeof(MDB_meta) - PAGEHDRSZ) *2);
	if (! rc && txn->mt_dbs[FREE_DBI].md_root != P_INVALID)
		rc = mdb_env_walk(&ctx, "free", txn->mt_dbs[FREE_DBI].md_root, 0, 0);
	if (! rc && txn->mt_dbs[MAIN_DBI].md_root != P_INVALID)
		rc = mdb_env_walk(&ctx, "main", txn->mt_dbs[MAIN_DBI].md_root, 0, 0);
	if (! rc)
		rc = visitor(P_INVALID, 0, user, NULL, NULL, 0, 0, 0, 0);
	return rc;
}

#endif /* MDBX_MODE_ENABLED */

/** @} */

#include "./midl.c"