From bc6a69073357c3bc9c4bde690da0c56f6002eada Mon Sep 17 00:00:00 2001
From: Leonid Yuriev <leo@yuriev.ru>
Date: Thu, 20 May 2021 12:29:59 +0300
Subject: [PATCH] mdbx: simplify & fix `mdbx_txn_keep()` and
 `mdbx_cursor_keep()`.

1 of 2 fixes for https://github.com/erthink/libmdbx/issues/195
---
 src/core.c | 63 ++++++++++++++++--------------------------------------
 1 file changed, 19 insertions(+), 44 deletions(-)

diff --git a/src/core.c b/src/core.c
index 8ae47b79..1afd3e01 100644
--- a/src/core.c
+++ b/src/core.c
@@ -4976,58 +4976,33 @@ static int spill_page(MDBX_txn *txn, struct mdbx_iov_ctx *ctx, MDBX_page *dp,
  * Returns the number of pages marked as unspillable. */
 static unsigned mdbx_cursor_keep(MDBX_txn *txn, MDBX_cursor *mc) {
   unsigned keep = 0;
-  if (!(mc->mc_flags & C_INITIALIZED))
-    return keep;
-
-loop:;
-  const MDBX_page *mp = NULL;
-  for (unsigned i = 0; i < mc->mc_snum; i++) {
-    mp = mc->mc_pg[i];
-    if (IS_MODIFIABLE(txn, mp)) {
-      unsigned const n = mdbx_dpl_search(txn, mp->mp_pgno);
-      if (txn->tw.dirtylist->items[n].pgno == mp->mp_pgno &&
-          txn->tw.dirtylist->items[n].lru != txn->tw.dirtylru) {
-        txn->tw.dirtylist->items[n].lru = txn->tw.dirtylru;
-        keep++;
+  while (mc->mc_flags & C_INITIALIZED) {
+    for (unsigned i = 0; i < mc->mc_snum; i++) {
+      const MDBX_page *mp = mc->mc_pg[i];
+      if (IS_MODIFIABLE(txn, mp) && !IS_SUBP(mp)) {
+        unsigned const n = mdbx_dpl_search(txn, mp->mp_pgno);
+        if (txn->tw.dirtylist->items[n].pgno == mp->mp_pgno &&
+            txn->tw.dirtylist->items[n].lru != txn->tw.dirtylru) {
+          txn->tw.dirtylist->items[n].lru = txn->tw.dirtylru;
+          keep++;
+        }
       }
     }
-  }
-  if (!(mp && IS_LEAF(mp)))
-    return keep;
-
-  /* Proceed to mx if it is at a sub-database */
-  MDBX_xcursor *mx = mc->mc_xcursor;
-  if (!(mx && (mx->mx_cursor.mc_flags & C_INITIALIZED)))
-    return keep;
-
-  const unsigned nkeys = page_numkeys(mp);
-  unsigned ki = mc->mc_ki[mc->mc_top];
-  mdbx_cassert(mc, nkeys > 0 &&
-                       (ki < nkeys ||
-                        (ki == nkeys && (mx->mx_cursor.mc_flags & C_EOF))));
-  ki -= ki >= nkeys;
-  if ((node_flags(page_node(mp, ki)) & F_SUBDATA)) {
-    mc = &mx->mx_cursor;
-    goto loop;
+    if (!mc->mc_xcursor)
+      break;
+    mc = &mc->mc_xcursor->mx_cursor;
   }
   return keep;
 }
 
 static unsigned mdbx_txn_keep(MDBX_txn *txn, MDBX_cursor *m0) {
   unsigned keep = m0 ? mdbx_cursor_keep(txn, m0) : 0;
-
-  for (unsigned i = FREE_DBI; i < txn->mt_numdbs; ++i) {
-    const pgno_t pgno = txn->mt_dbs[i].md_root;
-    if ((txn->mt_dbistate[i] & DBI_DIRTY) && pgno != P_INVALID) {
-      unsigned const n = mdbx_dpl_search(txn, pgno);
-      if (likely(txn->tw.dirtylist->items[n].pgno == pgno)) {
-        txn->tw.dirtylist->items[n].lru = txn->tw.dirtylru;
-        for (MDBX_cursor *mc = txn->tw.cursors[i]; mc; mc = mc->mc_next)
-          if (mc != m0)
-            keep += mdbx_cursor_keep(txn, mc);
-      }
-    }
-  }
+  for (unsigned i = FREE_DBI; i < txn->mt_numdbs; ++i)
+    if (F_ISSET(txn->mt_dbistate[i], DBI_DIRTY | DBI_VALID) &&
+        txn->mt_dbs[i].md_root != P_INVALID)
+      for (MDBX_cursor *mc = txn->tw.cursors[i]; mc; mc = mc->mc_next)
+        if (mc != m0)
+          keep += mdbx_cursor_keep(txn, mc);
   return keep;
 }