From c3b2c1fdef880f7a564859adfe26ba3bc4a77a62 Mon Sep 17 00:00:00 2001
From: Leonid Yuriev <leo@yuriev.ru>
Date: Wed, 28 Apr 2021 19:51:58 +0300
Subject: [PATCH] mdbx: handling the case when all dirty pages are unspillable.

Related to https://github.com/erthink/libmdbx/issues/186

Change-Id: Iff7a123c1c171371624d8b7ae497941ec4622385
---
 src/core.c | 125 ++++++++++++++++++++++++++++++-----------------------
 1 file changed, 71 insertions(+), 54 deletions(-)

diff --git a/src/core.c b/src/core.c
index 6c48a23d..fcf5927c 100644
--- a/src/core.c
+++ b/src/core.c
@@ -4828,59 +4828,6 @@ static __inline int mdbx_page_retire(MDBX_cursor *mc, MDBX_page *mp) {
   return mdbx_page_retire_ex(mc, mp->mp_pgno, mp, PAGETYPE(mp));
 }
 
-/* Set P_KEEP in dirty, non-overflow, non-sub pages watched by txn. */
-static void mdbx_cursor_keep(MDBX_txn *txn, MDBX_cursor *mc) {
-  if (!(mc->mc_flags & C_INITIALIZED))
-    return;
-
-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;
-    }
-  }
-  if (!(mp && IS_LEAF(mp)))
-    return;
-
-  /* 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;
-
-  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;
-  }
-}
-
-static void mdbx_txn_keep(MDBX_txn *txn, MDBX_cursor *m0) {
-  if (m0)
-    mdbx_cursor_keep(txn, m0);
-
-  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)
-            mdbx_cursor_keep(txn, mc);
-      }
-    }
-  }
-}
-
 struct mdbx_iov_ctx {
   unsigned iov_items;
   size_t iov_bytes;
@@ -5016,6 +4963,65 @@ static int spill_page(MDBX_txn *txn, struct mdbx_iov_ctx *ctx, MDBX_page *dp,
   return err;
 }
 
+/* Set unspillable LRU-label for dirty pages watched by txn.
+ * 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++;
+      }
+    }
+  }
+  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;
+  }
+  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);
+      }
+    }
+  }
+  return keep;
+}
+
 /* Returns the spilling priority (0..255) for a dirty page:
  *      0 = should be spilled;
  *    ...
@@ -5186,7 +5192,18 @@ static int mdbx_txn_spill(MDBX_txn *const txn, MDBX_cursor *const m0,
   MDBX_dpl *const dl = mdbx_dpl_sort(txn);
 
   /* Preserve pages which may soon be dirtied again */
-  mdbx_txn_keep(txn, m0);
+  const unsigned unspillable = mdbx_txn_keep(txn, m0);
+  if (unspillable + txn->tw.loose_count >= dl->length) {
+#if MDBX_DEBUG_SPILLING == 1 /* avoid false failure in debug mode  */
+    if (likely(txn->tw.dirtyroom + txn->tw.loose_count >= need))
+      return MDBX_SUCCESS;
+#endif /* MDBX_DEBUG_SPILLING */
+    mdbx_error("all %u dirty pages are unspillable  since referenced "
+               "by a cursor(s), use fewer cursors or increase "
+               "MDBX_opt_txn_dp_limit",
+               unspillable);
+    return MDBX_TXN_FULL;
+  }
 
   /* Подзадача: Вытолкнуть часть страниц на диск в соответствии с LRU,
    * но при этом учесть важные поправки: