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Fix race condition in relcache init file invalidation.

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The previous code tried to synchronize by unlinking the init file twice,
but that doesn't actually work: it leaves a window wherein a third process
could read the already-stale init file but miss the SI messages that would
tell it the data is stale.  The result would be bizarre failures in catalog
accesses, typically "could not read block 0 in file ..." later during
startup.

Instead, hold RelCacheInitLock across both the unlink and the sending of
the SI messages.  This is more straightforward, and might even be a bit
faster since only one unlink call is needed.

This has been wrong since it was put in (in 2002!), so back-patch to all
supported releases.
This commit is contained in:
Tom Lane
2011-08-16 13:12:03 -04:00
parent 0615782b23
commit 45476031a5
4 changed files with 57 additions and 49 deletions
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4
src/backend/access/transam/twophase.c
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@@ -1356,10 +1356,10 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
* after we send the SI messages. See AtEOXact_Inval()
*/
if (hdr->initfileinval)
RelationCacheInitFileInvalidate(true);
RelationCacheInitFilePreInvalidate();
SendSharedInvalidMessages(invalmsgs, hdr->ninvalmsgs);
if (hdr->initfileinval)
RelationCacheInitFileInvalidate(false);
RelationCacheInitFilePostInvalidate();
/* And now do the callbacks */
if (isCommit)