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Replace RelationOpenSmgr() with RelationGetSmgr().

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The idea behind this patch is to design out bugs like the one fixed
by commit 9d523119f.  Previously, once one did RelationOpenSmgr(rel),
it was considered okay to access rel->rd_smgr directly for some
not-very-clear interval.  But since that pointer will be cleared by
relcache flushes, we had bugs arising from overreliance on a previous
RelationOpenSmgr call still being effective.

Now, very little code except that in rel.h and relcache.c should ever
touch the rd_smgr field directly.  The normal coding rule is to use
RelationGetSmgr(rel) and not expect the result to be valid for longer
than one smgr function call.  There are a couple of places where using
the function every single time seemed like overkill, but they are now
annotated with large warning comments.

Amul Sul, after an idea of mine.

Discussion: https://postgr.es/m/CANiYTQsU7yMFpQYnv=BrcRVqK_3U3mtAzAsJCaqtzsDHfsUbdQ@mail.gmail.com
This commit is contained in:
Tom Lane
2021-07-12 17:01:29 -04:00
parent 5b60cf35f5
commit f10f0ae420
21 changed files with 164 additions and 165 deletions
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6
contrib/pg_visibility/pg_visibility.c
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@ -391,14 +391,14 @@ pg_truncate_visibility_map(PG_FUNCTION_ARGS)
/* Only some relkinds have a visibility map */
check_relation_relkind(rel);
RelationOpenSmgr(rel);
rel->rd_smgr->smgr_cached_nblocks[VISIBILITYMAP_FORKNUM] = InvalidBlockNumber;
/* Forcibly reset cached file size */
RelationGetSmgr(rel)->smgr_cached_nblocks[VISIBILITYMAP_FORKNUM] = InvalidBlockNumber;
block = visibilitymap_prepare_truncate(rel, 0);
if (BlockNumberIsValid(block))
{
fork = VISIBILITYMAP_FORKNUM;
smgrtruncate(rel->rd_smgr, &fork, 1, &block);
smgrtruncate(RelationGetSmgr(rel), &fork, 1, &block);
}
if (RelationNeedsWAL(rel))