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Implement prefetching via posix_fadvise() for bitmap index scans. A new

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GUC variable effective_io_concurrency controls how many concurrent block
prefetch requests will be issued.

(The best way to handle this for plain index scans is still under debate,
so that part is not applied yet --- tgl)

Greg Stark
This commit is contained in:
Tom Lane
2009-01-12 05:10:45 +00:00
parent 1a37056a74
commit b7b8f0b609
15 changed files with 422 additions and 17 deletions
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59
src/backend/storage/buffer/bufmgr.c
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@ -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;
@ -95,6 +102,56 @@ static void FlushBuffer(volatile BufferDesc *buf, SMgrRelation reln);
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.