From 624f155ffa93d1af4fb9d91fd5c0eb05da1e9e54 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Tue, 27 Sep 2011 08:24:18 -0400
Subject: [PATCH] heap_update() must recheck tuple after unlocking and
relocking buffer.
Bug found by Alvaro Herrera, fix suggested by Heikki Linnakangas
and reviewed by Tom Lane.
---
src/backend/access/heap/heapam.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 17950d482c1..b2d19016e76 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -2645,13 +2645,16 @@ l2:
* visible while we were busy locking the buffer, or during some subsequent
* window during which we had it unlocked, we'll have to unlock and
* re-lock, to avoid holding the buffer lock across an I/O. That's a bit
- * unfortunate, but hopefully shouldn't happen often.
+ * unfortunate, esepecially since we'll now have to recheck whether the
+ * tuple has been locked or updated under us, but hopefully it won't
+ * happen very often.
*/
if (vmbuffer == InvalidBuffer && PageIsAllVisible(page))
{
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
visibilitymap_pin(relation, block, &vmbuffer);
LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+ goto l2;
}
/*
--
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