diff options
Diffstat (limited to 'src/backend/storage/buffer/bufmgr.c')
| -rw-r--r-- | src/backend/storage/buffer/bufmgr.c | 59 |
1 files changed, 58 insertions, 1 deletions
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 6046f6ef6aa..534c7516f78 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.244 2009/01/01 17:23:47 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.245 2009/01/12 05:10:44 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -65,6 +65,13 @@ bool zero_damaged_pages = false; int bgwriter_lru_maxpages = 100; double bgwriter_lru_multiplier = 2.0; +/* + * How many buffers PrefetchBuffer callers should try to stay ahead of their + * ReadBuffer calls by. This is maintained by the assign hook for + * effective_io_concurrency. Zero means "never prefetch". + */ +int target_prefetch_pages = 0; + /* local state for StartBufferIO and related functions */ static volatile BufferDesc *InProgressBuf = NULL; static bool IsForInput; @@ -96,6 +103,56 @@ static void AtProcExit_Buffers(int code, Datum arg); /* + * PrefetchBuffer -- initiate asynchronous read of a block of a relation + * + * This is named by analogy to ReadBuffer but doesn't actually allocate a + * buffer. Instead it tries to ensure that a future ReadBuffer for the given + * block will not be delayed by the I/O. Prefetching is optional. + * No-op if prefetching isn't compiled in. + */ +void +PrefetchBuffer(Relation reln, ForkNumber forkNum, BlockNumber blockNum) +{ +#ifdef USE_PREFETCH + Assert(RelationIsValid(reln)); + Assert(BlockNumberIsValid(blockNum)); + + /* Open it at the smgr level if not already done */ + RelationOpenSmgr(reln); + + if (reln->rd_istemp) + { + /* pass it off to localbuf.c */ + LocalPrefetchBuffer(reln->rd_smgr, forkNum, blockNum); + } + else + { + BufferTag newTag; /* identity of requested block */ + uint32 newHash; /* hash value for newTag */ + LWLockId newPartitionLock; /* buffer partition lock for it */ + int buf_id; + + /* create a tag so we can lookup the buffer */ + INIT_BUFFERTAG(newTag, reln->rd_smgr->smgr_rnode, forkNum, blockNum); + + /* determine its hash code and partition lock ID */ + newHash = BufTableHashCode(&newTag); + newPartitionLock = BufMappingPartitionLock(newHash); + + /* see if the block is in the buffer pool already */ + LWLockAcquire(newPartitionLock, LW_SHARED); + buf_id = BufTableLookup(&newTag, newHash); + LWLockRelease(newPartitionLock); + + /* If not in buffers, initiate prefetch */ + if (buf_id < 0) + smgrprefetch(reln->rd_smgr, forkNum, blockNum); + } +#endif /* USE_PREFETCH */ +} + + +/* * ReadBuffer -- a shorthand for ReadBufferExtended, for reading from main * fork with RBM_NORMAL mode and default strategy. */ |