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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 13:11:54 -04:00
parent 1bb69245ab
commit 2ada6779c5
4 changed files with 57 additions and 49 deletions
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3
src/include/utils/relcache.h
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@ -98,7 +98,8 @@ extern void AtEOSubXact_RelationCache(bool isCommit, SubTransactionId mySubid,
* Routines to help manage rebuilding of relcache init files
*/
extern bool RelationIdIsInInitFile(Oid relationId);
extern void RelationCacheInitFileInvalidate(bool beforeSend);
extern void RelationCacheInitFilePreInvalidate(void);
extern void RelationCacheInitFilePostInvalidate(void);
extern void RelationCacheInitFileRemove(void);
/* should be used only by relcache.c and catcache.c */