From dc39ecfb9fc153b33063c3de1009aad3757f471c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=9B=D0=B5=D0=BE=D0=BD=D0=B8=D0=B4=20=D0=AE=D1=80=D1=8C?=
 =?UTF-8?q?=D0=B5=D0=B2=20=28Leonid=20Yuriev=29?= <leo@yuriev.ru>
Date: Sun, 24 Jul 2022 21:20:22 +0300
Subject: [PATCH] mdbx: auto-coalesce of GC's records with less overhead.

---
 src/core.c      | 20 +++++++-------------
 src/internals.h |  2 +-
 2 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/src/core.c b/src/core.c
index 65f1369c..991141a0 100644
--- a/src/core.c
+++ b/src/core.c
@@ -6645,19 +6645,18 @@ __hot static pgno_t *scan4range(const MDBX_PNL pnl, const unsigned len,
 #define MDBX_ALLOC_NOLOG 32
 #define MDBX_ALLOC_ALL (MDBX_ALLOC_GC | MDBX_ALLOC_NEW)
 
-__cold static pgr_t page_alloc_slowpath(MDBX_cursor *mc, const pgno_t num,
-                                        int flags) {
+static pgr_t page_alloc_slowpath(MDBX_cursor *mc, const pgno_t num, int flags) {
   pgr_t ret;
   MDBX_txn *const txn = mc->mc_txn;
   MDBX_env *const env = txn->mt_env;
   mdbx_assert(env, num == 0 || !(flags & MDBX_ALLOC_SLOT));
   mdbx_assert(env, num > 0 || !(flags & MDBX_ALLOC_NEW));
 
-  const unsigned coalesce_threshold =
-      env->me_maxgc_ov1page - env->me_maxgc_ov1page / 4;
+  const unsigned coalesce_threshold = env->me_maxgc_ov1page >> 2;
   if (likely(flags & MDBX_ALLOC_GC)) {
     flags |= env->me_flags & MDBX_LIFORECLAIM;
-    if (MDBX_PNL_SIZE(txn->tw.reclaimed_pglist) < coalesce_threshold)
+    if (txn->mt_dbs[FREE_DBI].md_branch_pages &&
+        MDBX_PNL_SIZE(txn->tw.reclaimed_pglist) < coalesce_threshold)
       flags |= MDBX_ALLOC_COALESCE;
     if (unlikely(
             /* If mc is updating the GC, then the retired-list cannot play
@@ -6858,7 +6857,6 @@ __cold static pgr_t page_alloc_slowpath(MDBX_cursor *mc, const pgno_t num,
       }
 
       /* Merge in descending sorted order */
-      const unsigned prev_re_len = MDBX_PNL_SIZE(re_list);
       pnl_merge(re_list, gc_pnl);
       if (mdbx_audit_enabled() &&
           unlikely(!mdbx_pnl_check(re_list, txn->mt_next_pgno))) {
@@ -6891,15 +6889,11 @@ __cold static pgr_t page_alloc_slowpath(MDBX_cursor *mc, const pgno_t num,
       }
 
       /* Don't try to coalesce too much. */
-      if (flags & MDBX_ALLOC_COALESCE) {
-        if (re_len /* current size */ > coalesce_threshold ||
-            (re_len > prev_re_len &&
-             re_len - prev_re_len /* delta from prev */ >=
-                 coalesce_threshold / 2)) {
+      if (re_len /* current size */ > coalesce_threshold) {
+        if (flags & MDBX_ALLOC_COALESCE)
           mdbx_trace("clear %s %s", "MDBX_ALLOC_COALESCE",
                      "since got threshold");
-          flags &= ~MDBX_ALLOC_COALESCE;
-        }
+        flags &= ~MDBX_ALLOC_COALESCE;
       }
     }
 
diff --git a/src/internals.h b/src/internals.h
index dff6b216..cc2a578a 100644
--- a/src/internals.h
+++ b/src/internals.h
@@ -1109,7 +1109,7 @@ struct MDBX_env {
 #define MDBX_ENV_TXKEY UINT32_C(0x10000000)
   /* Legacy MDBX_MAPASYNC (prior v0.9) */
 #define MDBX_DEPRECATED_MAPASYNC UINT32_C(0x100000)
-  /* Legacy MDBX_MAPASYNC (prior v0.12) */
+  /* Legacy MDBX_COALESCE (prior v0.12) */
 #define MDBX_DEPRECATED_COALESCE UINT32_C(0x2000000)
 #define ENV_INTERNAL_FLAGS (MDBX_FATAL_ERROR | MDBX_ENV_ACTIVE | MDBX_ENV_TXKEY)
   uint32_t me_flags;