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Tom Lane 08e261cbc9 Fix race condition with toast table access from a stale syscache entry. ... If a tuple in a syscache contains an out-of-line toasted field, and we try to fetch that field shortly after some other transaction has committed an update or deletion of the tuple, there is a race condition: vacuum could come along and remove the toast tuples before we can fetch them. This leads to transient failures like "missing chunk number 0 for toast value NNNNN in pg_toast_2619", as seen in recent reports from Andrew Hammond and Tim Uckun. The design idea of syscache is that access to stale syscache entries should be prevented by relation-level locks, but that fails for at least two cases where toasted fields are possible: ANALYZE updates pg_statistic rows without locking out sessions that might want to plan queries on the same table, and CREATE OR REPLACE FUNCTION updates pg_proc rows without any meaningful lock at all. The least risky fix seems to be an idea that Heikki suggested when we were dealing with a related problem back in August: forcibly detoast any out-of-line fields before putting a tuple into syscache in the first place. This avoids the problem because at the time we fetch the parent tuple from the catalog, we should be holding an MVCC snapshot that will prevent removal of the toast tuples, even if the parent tuple is outdated immediately after we fetch it. (Note: I'm not convinced that this statement holds true at every instant where we could be fetching a syscache entry at all, but it does appear to hold true at the times where we could fetch an entry that could have a toasted field. We will need to be a bit wary of adding toast tables to low-level catalogs that don't have them already.) An additional benefit is that subsequent uses of the syscache entry should be faster, since they won't have to detoast the field. Back-patch to all supported versions. The problem is significantly harder to reproduce in pre-9.0 releases, because of their willingness to flush every entry in a syscache whenever the underlying catalog is vacuumed (cf CatalogCacheFlushRelation); but there is still a window for trouble.		14 years ago
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Makefile	Remove cvs keywords from all files.	15 years ago
attoptcache.c	Remove unnecessary #include references, per pgrminclude script.	14 years ago
catcache.c	Fix race condition with toast table access from a stale syscache entry.	14 years ago
inval.c	Improve comment about handling of temp tables in shared-inval code.	14 years ago
lsyscache.c	Remove assumptions that not-equals operators cannot be in any opclass.	14 years ago
plancache.c	Use a fresh copy of query_list when making a second plan in GetCachedPlan.	14 years ago
relcache.c	Measure the number of all-visible pages for use in index-only scan costing.	14 years ago
relmapper.c	Clean up the #include mess a little.	14 years ago
spccache.c	Clean up the #include mess a little.	14 years ago
syscache.c	Capitalization fixes	14 years ago
ts_cache.c	Remove unnecessary #include references, per pgrminclude script.	14 years ago
typcache.c	Remove unnecessary #include references, per pgrminclude script.	14 years ago