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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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24
src/backend/storage/buffer/bufmgr.c
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@ -589,9 +589,6 @@ PrefetchBuffer(Relation reln, ForkNumber forkNum, BlockNumber blockNum)
Assert(RelationIsValid(reln));
Assert(BlockNumberIsValid(blockNum));
/* Open it at the smgr level if not already done */
RelationOpenSmgr(reln);
if (RelationUsesLocalBuffers(reln))
{
/* see comments in ReadBufferExtended */
@ -601,12 +598,12 @@ PrefetchBuffer(Relation reln, ForkNumber forkNum, BlockNumber blockNum)
errmsg("cannot access temporary tables of other sessions")));
/* pass it off to localbuf.c */
return PrefetchLocalBuffer(reln->rd_smgr, forkNum, blockNum);
return PrefetchLocalBuffer(RelationGetSmgr(reln), forkNum, blockNum);
}
else
{
/* pass it to the shared buffer version */
return PrefetchSharedBuffer(reln->rd_smgr, forkNum, blockNum);
return PrefetchSharedBuffer(RelationGetSmgr(reln), forkNum, blockNum);
}
}
@ -747,9 +744,6 @@ ReadBufferExtended(Relation reln, ForkNumber forkNum, BlockNumber blockNum,
bool hit;
Buffer buf;
/* Open it at the smgr level if not already done */
RelationOpenSmgr(reln);
/*
* Reject attempts to read non-local temporary relations; we would be
* likely to get wrong data since we have no visibility into the owning
@ -765,7 +759,7 @@ ReadBufferExtended(Relation reln, ForkNumber forkNum, BlockNumber blockNum,
* miss.
*/
pgstat_count_buffer_read(reln);
buf = ReadBuffer_common(reln->rd_smgr, reln->rd_rel->relpersistence,
buf = ReadBuffer_common(RelationGetSmgr(reln), reln->rd_rel->relpersistence,
forkNum, blockNum, mode, strategy, &hit);
if (hit)
pgstat_count_buffer_hit(reln);
@ -2949,10 +2943,7 @@ RelationGetNumberOfBlocksInFork(Relation relation, ForkNumber forkNum)
case RELKIND_SEQUENCE:
case RELKIND_INDEX:
case RELKIND_PARTITIONED_INDEX:
/* Open it at the smgr level if not already done */
RelationOpenSmgr(relation);
return smgrnblocks(relation->rd_smgr, forkNum);
return smgrnblocks(RelationGetSmgr(relation), forkNum);
case RELKIND_RELATION:
case RELKIND_TOASTVALUE:
@ -3527,9 +3518,6 @@ FlushRelationBuffers(Relation rel)
int i;
BufferDesc *bufHdr;
/* Open rel at the smgr level if not already done */
RelationOpenSmgr(rel);
if (RelationUsesLocalBuffers(rel))
{
for (i = 0; i < NLocBuffer; i++)
@ -3554,7 +3542,7 @@ FlushRelationBuffers(Relation rel)
PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
smgrwrite(rel->rd_smgr,
smgrwrite(RelationGetSmgr(rel),
bufHdr->tag.forkNum,
bufHdr->tag.blockNum,
localpage,
@ -3595,7 +3583,7 @@ FlushRelationBuffers(Relation rel)
{
PinBuffer_Locked(bufHdr);
LWLockAcquire(BufferDescriptorGetContentLock(bufHdr), LW_SHARED);
FlushBuffer(bufHdr, rel->rd_smgr);
FlushBuffer(bufHdr, RelationGetSmgr(rel));
LWLockRelease(BufferDescriptorGetContentLock(bufHdr));
UnpinBuffer(bufHdr, true);
}