From d60e6f15180a40b117b3fc9b330967e52a5b6485 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Tue, 17 Mar 2020 17:26:41 +1300 Subject: [PATCH 4/5] Allow PrefetchBuffer() to report what happened. Report whether a prefetch was actually initiated, so that callers can limit the number of concurrent I/Os they try to issue, without counting the prefetch calls that did nothing because the page was already in our buffers. Also report when a relation's backing file is missing, to prepare for use during recovery. This will be used to handle cases of relations that are referenced in the WAL but have been unlinked already due to actions covered by WAL records that haven't been replayed yet, after a crash. Reviewed-by: Alvaro Herrera Discussion: https://postgr.es/m/CA%2BhUKGJ4VJN8ttxScUFM8dOKX0BrBiboo5uz1cq%3DAovOddfHpA%40mail.gmail.com --- src/backend/storage/buffer/bufmgr.c | 15 ++++++++++----- src/backend/storage/buffer/localbuf.c | 7 +++++-- src/backend/storage/smgr/md.c | 9 +++++++-- src/backend/storage/smgr/smgr.c | 10 +++++++--- src/include/storage/buf_internals.h | 5 +++-- src/include/storage/bufmgr.h | 17 ++++++++++++----- src/include/storage/md.h | 2 +- src/include/storage/smgr.h | 2 +- 8 files changed, 46 insertions(+), 21 deletions(-) diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index d30aed6fd9..b13e05cce8 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -469,7 +469,7 @@ static int ts_ckpt_progress_comparator(Datum a, Datum b, void *arg); /* * Implementation of PrefetchBuffer() for shared buffers. */ -void +PrefetchBufferResult PrefetchSharedBuffer(struct SMgrRelationData *smgr_reln, ForkNumber forkNum, BlockNumber blockNum) @@ -497,7 +497,11 @@ PrefetchSharedBuffer(struct SMgrRelationData *smgr_reln, /* If not in buffers, initiate prefetch */ if (buf_id < 0) - smgrprefetch(smgr_reln, forkNum, blockNum); + { + if (!smgrprefetch(smgr_reln, forkNum, blockNum)) + return PREFETCH_BUFFER_NOREL; + return PREFETCH_BUFFER_MISS; + } /* * If the block *is* in buffers, we do nothing. This is not really ideal: @@ -511,6 +515,7 @@ PrefetchSharedBuffer(struct SMgrRelationData *smgr_reln, * a problem to justify that. */ #endif /* USE_PREFETCH */ + return PREFETCH_BUFFER_HIT; } /* @@ -521,7 +526,7 @@ PrefetchSharedBuffer(struct SMgrRelationData *smgr_reln, * block will not be delayed by the I/O. Prefetching is optional. * No-op if prefetching isn't compiled in. */ -void +PrefetchBufferResult PrefetchBuffer(Relation reln, ForkNumber forkNum, BlockNumber blockNum) { #ifdef USE_PREFETCH @@ -540,12 +545,12 @@ PrefetchBuffer(Relation reln, ForkNumber forkNum, BlockNumber blockNum) errmsg("cannot access temporary tables of other sessions"))); /* pass it off to localbuf.c */ - PrefetchLocalBuffer(reln->rd_smgr, forkNum, blockNum); + return PrefetchLocalBuffer(reln->rd_smgr, forkNum, blockNum); } else { /* pass it to the shared buffer version */ - PrefetchSharedBuffer(reln->rd_smgr, forkNum, blockNum); + return PrefetchSharedBuffer(reln->rd_smgr, forkNum, blockNum); } #endif /* USE_PREFETCH */ } diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c index b528bc9553..c728986e12 100644 --- a/src/backend/storage/buffer/localbuf.c +++ b/src/backend/storage/buffer/localbuf.c @@ -60,7 +60,7 @@ static Block GetLocalBufferStorage(void); * Do PrefetchBuffer's work for temporary relations. * No-op if prefetching isn't compiled in. */ -void +PrefetchBufferResult PrefetchLocalBuffer(SMgrRelation smgr, ForkNumber forkNum, BlockNumber blockNum) { @@ -81,11 +81,14 @@ PrefetchLocalBuffer(SMgrRelation smgr, ForkNumber forkNum, if (hresult) { /* Yes, so nothing to do */ - return; + return PREFETCH_BUFFER_HIT; } /* Not in buffers, so initiate prefetch */ smgrprefetch(smgr, forkNum, blockNum); + return PREFETCH_BUFFER_MISS; +#else + return PREFETCH_BUFFER_HIT; #endif /* USE_PREFETCH */ } diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c index c5b771c531..ba12fc2077 100644 --- a/src/backend/storage/smgr/md.c +++ b/src/backend/storage/smgr/md.c @@ -525,14 +525,17 @@ mdclose(SMgrRelation reln, ForkNumber forknum) /* * mdprefetch() -- Initiate asynchronous read of the specified block of a relation */ -void +bool mdprefetch(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum) { #ifdef USE_PREFETCH off_t seekpos; MdfdVec *v; - v = _mdfd_getseg(reln, forknum, blocknum, false, EXTENSION_FAIL); + v = _mdfd_getseg(reln, forknum, blocknum, false, + InRecovery ? EXTENSION_RETURN_NULL : EXTENSION_FAIL); + if (v == NULL) + return false; seekpos = (off_t) BLCKSZ * (blocknum % ((BlockNumber) RELSEG_SIZE)); @@ -540,6 +543,8 @@ mdprefetch(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum) (void) FilePrefetch(v->mdfd_vfd, seekpos, BLCKSZ, WAIT_EVENT_DATA_FILE_PREFETCH); #endif /* USE_PREFETCH */ + + return true; } /* diff --git a/src/backend/storage/smgr/smgr.c b/src/backend/storage/smgr/smgr.c index 360b5bf5bf..c39dd533e6 100644 --- a/src/backend/storage/smgr/smgr.c +++ b/src/backend/storage/smgr/smgr.c @@ -49,7 +49,7 @@ typedef struct f_smgr bool isRedo); void (*smgr_extend) (SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, char *buffer, bool skipFsync); - void (*smgr_prefetch) (SMgrRelation reln, ForkNumber forknum, + bool (*smgr_prefetch) (SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum); void (*smgr_read) (SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, char *buffer); @@ -489,11 +489,15 @@ smgrextend(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, /* * smgrprefetch() -- Initiate asynchronous read of the specified block of a relation. + * + * In recovery only, this can return false to indicate that a file + * doesn't exist (presumably it has been dropped by a later WAL + * record). */ -void +bool smgrprefetch(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum) { - smgrsw[reln->smgr_which].smgr_prefetch(reln, forknum, blocknum); + return smgrsw[reln->smgr_which].smgr_prefetch(reln, forknum, blocknum); } /* diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h index 166fe334c7..e57f84ee9c 100644 --- a/src/include/storage/buf_internals.h +++ b/src/include/storage/buf_internals.h @@ -327,8 +327,9 @@ extern int BufTableInsert(BufferTag *tagPtr, uint32 hashcode, int buf_id); extern void BufTableDelete(BufferTag *tagPtr, uint32 hashcode); /* localbuf.c */ -extern void PrefetchLocalBuffer(SMgrRelation smgr, ForkNumber forkNum, - BlockNumber blockNum); +extern PrefetchBufferResult PrefetchLocalBuffer(SMgrRelation smgr, + ForkNumber forkNum, + BlockNumber blockNum); extern BufferDesc *LocalBufferAlloc(SMgrRelation smgr, ForkNumber forkNum, BlockNumber blockNum, bool *foundPtr); extern void MarkLocalBufferDirty(Buffer buffer); diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index e00dd3ffb7..1210d1e7e8 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -159,14 +159,21 @@ extern PGDLLIMPORT int32 *LocalRefCount; */ #define BufferGetPage(buffer) ((Page)BufferGetBlock(buffer)) +typedef enum PrefetchBufferResult +{ + PREFETCH_BUFFER_HIT, + PREFETCH_BUFFER_MISS, + PREFETCH_BUFFER_NOREL +} PrefetchBufferResult; + /* * prototypes for functions in bufmgr.c */ -extern void PrefetchSharedBuffer(struct SMgrRelationData *smgr_reln, - ForkNumber forkNum, - BlockNumber blockNum); -extern void PrefetchBuffer(Relation reln, ForkNumber forkNum, - BlockNumber blockNum); +extern PrefetchBufferResult PrefetchSharedBuffer(struct SMgrRelationData *smgr_reln, + ForkNumber forkNum, + BlockNumber blockNum); +extern PrefetchBufferResult PrefetchBuffer(Relation reln, ForkNumber forkNum, + BlockNumber blockNum); extern Buffer ReadBuffer(Relation reln, BlockNumber blockNum); extern Buffer ReadBufferExtended(Relation reln, ForkNumber forkNum, BlockNumber blockNum, ReadBufferMode mode, diff --git a/src/include/storage/md.h b/src/include/storage/md.h index ec7630ce3b..07fd1bb7d0 100644 --- a/src/include/storage/md.h +++ b/src/include/storage/md.h @@ -28,7 +28,7 @@ extern bool mdexists(SMgrRelation reln, ForkNumber forknum); extern void mdunlink(RelFileNodeBackend rnode, ForkNumber forknum, bool isRedo); extern void mdextend(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, char *buffer, bool skipFsync); -extern void mdprefetch(SMgrRelation reln, ForkNumber forknum, +extern bool mdprefetch(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum); extern void mdread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, char *buffer); diff --git a/src/include/storage/smgr.h b/src/include/storage/smgr.h index 243822137c..dc740443e2 100644 --- a/src/include/storage/smgr.h +++ b/src/include/storage/smgr.h @@ -92,7 +92,7 @@ extern void smgrdounlink(SMgrRelation reln, bool isRedo); extern void smgrdounlinkall(SMgrRelation *rels, int nrels, bool isRedo); extern void smgrextend(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, char *buffer, bool skipFsync); -extern void smgrprefetch(SMgrRelation reln, ForkNumber forknum, +extern bool smgrprefetch(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum); extern void smgrread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum, char *buffer); -- 2.20.1