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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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12
src/backend/executor/nodeIndexscan.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/nodeIndexscan.c,v 1.92 2004/02/28 19:46:05 tgl Exp $
* $PostgreSQL: pgsql/src/backend/executor/nodeIndexscan.c,v 1.93 2004/04/21 18:24:26 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -128,6 +128,15 @@ IndexNext(IndexScanState *node)
slot = node->ss.ss_ScanTupleSlot;
scanrelid = ((IndexScan *) node->ss.ps.plan)->scan.scanrelid;
/*
* Clear any reference to the previously returned tuple. The idea here
* is to not have the tuple slot be the last holder of a pin on that
* tuple's buffer; if it is, we'll need a separate visit to the bufmgr
* to release the buffer. By clearing here, we get to have the release
* done by ReleaseAndReadBuffer inside index_getnext.
*/
ExecClearTuple(slot);
/*
* Check if we are evaluating PlanQual for tuple of this relation.
* Additional checking is not good, but no other way for now. We could
@ -139,7 +148,6 @@ IndexNext(IndexScanState *node)
{
List *qual;
ExecClearTuple(slot);
if (estate->es_evTupleNull[scanrelid - 1])
return slot; /* return empty slot */

12
src/backend/executor/nodeSeqscan.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/nodeSeqscan.c,v 1.47 2003/11/29 19:51:48 pgsql Exp $
* $PostgreSQL: pgsql/src/backend/executor/nodeSeqscan.c,v 1.48 2004/04/21 18:24:26 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -61,6 +61,15 @@ SeqNext(SeqScanState *node)
direction = estate->es_direction;
slot = node->ss_ScanTupleSlot;
/*
* Clear any reference to the previously returned tuple. The idea here
* is to not have the tuple slot be the last holder of a pin on that
* tuple's buffer; if it is, we'll need a separate visit to the bufmgr
* to release the buffer. By clearing here, we get to have the release
* done by ReleaseAndReadBuffer inside heap_getnext.
*/
ExecClearTuple(slot);
/*
* Check if we are evaluating PlanQual for tuple of this relation.
* Additional checking is not good, but no other way for now. We could
@ -70,7 +79,6 @@ SeqNext(SeqScanState *node)
if (estate->es_evTuple != NULL &&
estate->es_evTuple[scanrelid - 1] != NULL)
{
ExecClearTuple(slot);
if (estate->es_evTupleNull[scanrelid - 1])
return slot; /* return empty slot */

10
src/backend/executor/nodeTidscan.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/nodeTidscan.c,v 1.36 2003/11/29 19:51:48 pgsql Exp $
* $PostgreSQL: pgsql/src/backend/executor/nodeTidscan.c,v 1.37 2004/04/21 18:24:26 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -106,6 +106,13 @@ TidNext(TidScanState *node)
slot = node->ss.ss_ScanTupleSlot;
scanrelid = ((TidScan *) node->ss.ps.plan)->scan.scanrelid;
/*
* Clear any reference to the previously returned tuple. This doesn't
* offer any great performance benefit, but it keeps this code in sync
* with SeqNext and IndexNext.
*/
ExecClearTuple(slot);
/*
* Check if we are evaluating PlanQual for tuple of this relation.
* Additional checking is not good, but no other way for now. We could
@ -115,7 +122,6 @@ TidNext(TidScanState *node)
if (estate->es_evTuple != NULL &&
estate->es_evTuple[scanrelid - 1] != NULL)
{
ExecClearTuple(slot);
if (estate->es_evTupleNull[scanrelid - 1])
return slot; /* return empty slot */