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Tweak indexscan and seqscan code to arrange that steps from one page to

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the next are handled by ReleaseAndReadBuffer rather than separate
ReleaseBuffer and ReadBuffer calls.  This cuts the number of acquisitions
of the BufMgrLock by a factor of 2 (possibly more, if an indexscan happens
to pull successive rows from the same heap page).  Unfortunately this
doesn't seem enough to get us out of the recently discussed context-switch
storm problem, but it's surely worth doing anyway.
This commit is contained in:
Tom Lane
2004-04-21 18:24:26 +00:00
parent 95a03e9cdf
commit 37fa3b6c89
11 changed files with 132 additions and 65 deletions
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29
src/backend/access/heap/heapam.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.164 2004/04/01 21:28:43 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.165 2004/04/21 18:24:23 tgl Exp $
*
*
* INTERFACE ROUTINES
@ -888,6 +888,28 @@ heap_fetch(Relation relation,
Buffer *userbuf,
bool keep_buf,
PgStat_Info *pgstat_info)
{
/* Assume *userbuf is undefined on entry */
*userbuf = InvalidBuffer;
return heap_release_fetch(relation, snapshot, tuple,
userbuf, keep_buf, pgstat_info);
}
/*
* heap_release_fetch - retrieve tuple with given tid
*
* This has the same API as heap_fetch except that if *userbuf is not
* InvalidBuffer on entry, that buffer will be released before reading
* the new page. This saves a separate ReleaseBuffer step and hence
* one entry into the bufmgr when looping through multiple fetches.
*/
bool
heap_release_fetch(Relation relation,
Snapshot snapshot,
HeapTuple tuple,
Buffer *userbuf,
bool keep_buf,
PgStat_Info *pgstat_info)
{
ItemPointer tid = &(tuple->t_self);
ItemId lp;
@ -898,9 +920,10 @@ heap_fetch(Relation relation,
/*
* get the buffer from the relation descriptor. Note that this does a
* buffer pin.
* buffer pin, and releases the old *userbuf if not InvalidBuffer.
*/
buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
buffer = ReleaseAndReadBuffer(*userbuf, relation,
ItemPointerGetBlockNumber(tid));
if (!BufferIsValid(buffer))
elog(ERROR, "ReadBuffer(\"%s\", %lu) failed",