Fix race condition in relcache init file invalidation.
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.
Branch
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REL8_4_STABLE
Details
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http://git.postgresql.org/pg/commitdiff/bcc9b17bbf92d1d94581d5536770b9689a767c37
Modified Files
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src/backend/utils/cache/inval.c | 8 ++--
src/backend/utils/cache/relcache.c | 68 +++++++++++++++++++----------------
src/include/utils/relcache.h | 3 +-
3 files changed, 43 insertions(+), 36 deletions(-)