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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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7
src/backend/commands/tablecmds.c
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@ -14151,7 +14151,6 @@ index_copy_data(Relation rel, RelFileNode newrnode)
SMgrRelation dstrel;
dstrel = smgropen(newrnode, rel->rd_backend);
RelationOpenSmgr(rel);
/*
* Since we copy the file directly without looking at the shared buffers,
@ -14171,14 +14170,14 @@ index_copy_data(Relation rel, RelFileNode newrnode)
RelationCreateStorage(newrnode, rel->rd_rel->relpersistence);
/* copy main fork */
RelationCopyStorage(rel->rd_smgr, dstrel, MAIN_FORKNUM,
RelationCopyStorage(RelationGetSmgr(rel), dstrel, MAIN_FORKNUM,
rel->rd_rel->relpersistence);
/* copy those extra forks that exist */
for (ForkNumber forkNum = MAIN_FORKNUM + 1;
forkNum <= MAX_FORKNUM; forkNum++)
{
if (smgrexists(rel->rd_smgr, forkNum))
if (smgrexists(RelationGetSmgr(rel), forkNum))
{
smgrcreate(dstrel, forkNum, false);
@ -14190,7 +14189,7 @@ index_copy_data(Relation rel, RelFileNode newrnode)
(rel->rd_rel->relpersistence == RELPERSISTENCE_UNLOGGED &&
forkNum == INIT_FORKNUM))
log_smgrcreate(&newrnode, forkNum);
RelationCopyStorage(rel->rd_smgr, dstrel, forkNum,
RelationCopyStorage(RelationGetSmgr(rel), dstrel, forkNum,
rel->rd_rel->relpersistence);
}
}