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heap_update() must recheck tuple after unlocking and relocking buffer.

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Bug found by Alvaro Herrera, fix suggested by Heikki Linnakangas
and reviewed by Tom Lane.
This commit is contained in:
Robert Haas 2011-09-27 08:24:18 -04:00
parent 269c5dd2f4
commit 624f155ffa
1 changed files with 4 additions and 1 deletions
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5
src/backend/access/heap/heapam.c
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@ -2645,13 +2645,16 @@ l2:
* visible while we were busy locking the buffer, or during some subsequent * 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 * 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 * 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)) if (vmbuffer == InvalidBuffer && PageIsAllVisible(page))
{ {
LockBuffer(buffer, BUFFER_LOCK_UNLOCK); LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
visibilitymap_pin(relation, block, &vmbuffer); visibilitymap_pin(relation, block, &vmbuffer);
LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE); LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
goto l2;
} }
/* /*