From 0c4b39bd119dfe995f7a91195679615db35c7d02 Mon Sep 17 00:00:00 2001
From: Leo Yuriev <leo@yuriev.ru>
Date: Fri, 4 May 2018 17:22:59 +0300
Subject: [PATCH] mdbx: fix wrong freeDB search.

Avoid search freeDB while tree is updating.
Bug was inherited from LMDB.
https://github.com/leo-yuriev/libmdbx/issues/31
---
 mdb.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mdb.c b/mdb.c
index 43f95cb0..740ad00d 100644
--- a/mdb.c
+++ b/mdb.c
@@ -2140,6 +2140,10 @@ mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp, int flags)
 			/* If mc is updating the freeDB, then the freelist cannot play
 			 * catch-up with itself by growing while trying to save it. */
 			flags &= ~(MDBX_ALLOC_GC | MDBX_ALLOC_KICK | MDBX_COALESCE | MDBX_LIFORECLAIM);
+		} else if (unlikely(txn->mt_dbs[FREE_DBI].md_entries == 0)) {
+			/* avoid (recursive) search inside empty tree and while tree is updating,
+			 * https://github.com/leo-yuriev/libmdbx/issues/31 */
+			flags &= ~MDBX_ALLOC_GC;
 		}
 	}