From 8aaa04b32d790da595684de58ae4fc2db96becff Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Thu, 30 Mar 2023 19:22:40 -0700 Subject: Track shared buffer hits in pg_stat_io Among other things, this should make it easier to calculate a useful cache hit ratio by excluding buffer reads via buffer access strategies. As buffer access strategies reuse buffers (and thus evict the prior buffer contents), it is normal to see reads on repeated scans of the same data. Author: Melanie Plageman Reviewed-by: Bertrand Drouvot Reviewed-by: Andres Freund Discussion: https://postgr.es/m/CAAKRu_beMa9Hzih40%3DXPYqhDVz6tsgUGTrhZXRo%3Dunp%2Bszb%3DUA%40mail.gmail.com --- src/backend/storage/buffer/bufmgr.c | 38 ++++++++++++++----------------------- 1 file changed, 14 insertions(+), 24 deletions(-) (limited to 'src/backend/storage/buffer/bufmgr.c') diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index fe029d2ea60..b3adbbe7d23 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -472,7 +472,7 @@ static BufferDesc *BufferAlloc(SMgrRelation smgr, ForkNumber forkNum, BlockNumber blockNum, BufferAccessStrategy strategy, - bool *foundPtr, IOContext *io_context); + bool *foundPtr, IOContext io_context); static void FlushBuffer(BufferDesc *buf, SMgrRelation reln, IOObject io_object, IOContext io_context); static void FindAndDropRelationBuffers(RelFileLocator rlocator, @@ -850,13 +850,14 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, if (isLocalBuf) { /* - * LocalBufferAlloc() will set the io_context to IOCONTEXT_NORMAL. We - * do not use a BufferAccessStrategy for I/O of temporary tables. + * We do not use a BufferAccessStrategy for I/O of temporary tables. * However, in some cases, the "strategy" may not be NULL, so we can't * rely on IOContextForStrategy() to set the right IOContext for us. * This may happen in cases like CREATE TEMPORARY TABLE AS... */ - bufHdr = LocalBufferAlloc(smgr, forkNum, blockNum, &found, &io_context); + io_context = IOCONTEXT_NORMAL; + io_object = IOOBJECT_TEMP_RELATION; + bufHdr = LocalBufferAlloc(smgr, forkNum, blockNum, &found); if (found) pgBufferUsage.local_blks_hit++; else if (isExtend) @@ -871,8 +872,10 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, * lookup the buffer. IO_IN_PROGRESS is set if the requested block is * not currently in memory. */ + io_context = IOContextForStrategy(strategy); + io_object = IOOBJECT_RELATION; bufHdr = BufferAlloc(smgr, relpersistence, forkNum, blockNum, - strategy, &found, &io_context); + strategy, &found, io_context); if (found) pgBufferUsage.shared_blks_hit++; else if (isExtend) @@ -892,6 +895,7 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, /* Just need to update stats before we exit */ *hit = true; VacuumPageHit++; + pgstat_count_io_op(io_object, io_context, IOOP_HIT); if (VacuumCostActive) VacuumCostBalance += VacuumCostPageHit; @@ -987,16 +991,7 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, */ Assert(!(pg_atomic_read_u32(&bufHdr->state) & BM_VALID)); /* spinlock not needed */ - if (isLocalBuf) - { - bufBlock = LocalBufHdrGetBlock(bufHdr); - io_object = IOOBJECT_TEMP_RELATION; - } - else - { - bufBlock = BufHdrGetBlock(bufHdr); - io_object = IOOBJECT_RELATION; - } + bufBlock = isLocalBuf ? LocalBufHdrGetBlock(bufHdr) : BufHdrGetBlock(bufHdr); if (isExtend) { @@ -1139,7 +1134,7 @@ static BufferDesc * BufferAlloc(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, BlockNumber blockNum, BufferAccessStrategy strategy, - bool *foundPtr, IOContext *io_context) + bool *foundPtr, IOContext io_context) { bool from_ring; BufferTag newTag; /* identity of requested block */ @@ -1193,11 +1188,8 @@ BufferAlloc(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, { /* * If we get here, previous attempts to read the buffer must - * have failed ... but we shall bravely try again. Set - * io_context since we will in fact need to count an IO - * Operation. + * have failed ... but we shall bravely try again. */ - *io_context = IOContextForStrategy(strategy); *foundPtr = false; } } @@ -1211,8 +1203,6 @@ BufferAlloc(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, */ LWLockRelease(newPartitionLock); - *io_context = IOContextForStrategy(strategy); - /* Loop here in case we have to try another victim buffer */ for (;;) { @@ -1295,7 +1285,7 @@ BufferAlloc(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, smgr->smgr_rlocator.locator.dbOid, smgr->smgr_rlocator.locator.relNumber); - FlushBuffer(buf, NULL, IOOBJECT_RELATION, *io_context); + FlushBuffer(buf, NULL, IOOBJECT_RELATION, io_context); LWLockRelease(BufferDescriptorGetContentLock(buf)); ScheduleBufferTagForWriteback(&BackendWritebackContext, @@ -1494,7 +1484,7 @@ BufferAlloc(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, * we may have been forced to release the buffer due to concurrent * pinners or erroring out. */ - pgstat_count_io_op(IOOBJECT_RELATION, *io_context, + pgstat_count_io_op(IOOBJECT_RELATION, io_context, from_ring ? IOOP_REUSE : IOOP_EVICT); } -- cgit v1.2.3