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Small performance improvement for hash joins and hash aggregation:

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when the plan is ReScanned, we don't have to rebuild the hash table
if there is no parameter change for its child node.  This idea has
been used for a long time in Sort and Material nodes, but was not in
the hash code till now.
This commit is contained in:
Tom Lane
2003-05-30 20:23:10 +00:00
parent 776d530924
commit d24d75ff19
2 changed files with 76 additions and 40 deletions
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33
src/backend/executor/nodeAgg.c
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@ -45,7 +45,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/executor/nodeAgg.c,v 1.104 2003/02/09 00:30:39 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/executor/nodeAgg.c,v 1.105 2003/05/30 20:23:10 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -1374,6 +1374,31 @@ ExecReScanAgg(AggState *node, ExprContext *exprCtxt)
ExprContext *econtext = node->ss.ps.ps_ExprContext;
int aggno;
node->agg_done = false;
if (((Agg *) node->ss.ps.plan)->aggstrategy == AGG_HASHED)
{
/*
* In the hashed case, if we haven't yet built the hash table
* then we can just return; nothing done yet, so nothing to undo.
* If subnode's chgParam is not NULL then it will be re-scanned by
* ExecProcNode, else no reason to re-scan it at all.
*/
if (!node->table_filled)
return;
/*
* If we do have the hash table and the subplan does not have any
* parameter changes, then we can just rescan the existing hash
* table; no need to build it again.
*/
if (((PlanState *) node)->lefttree->chgParam == NULL)
{
ResetTupleHashIterator(&node->hashiter);
return;
}
}
/* Make sure we have closed any open tuplesorts */
for (aggno = 0; aggno < node->numaggs; aggno++)
{
@ -1384,19 +1409,23 @@ ExecReScanAgg(AggState *node, ExprContext *exprCtxt)
peraggstate->sortstate = NULL;
}
node->agg_done = false;
/* Release first tuple of group, if we have made a copy */
if (node->grp_firstTuple != NULL)
{
heap_freetuple(node->grp_firstTuple);
node->grp_firstTuple = NULL;
}
/* Forget current agg values */
MemSet(econtext->ecxt_aggvalues, 0, sizeof(Datum) * node->numaggs);
MemSet(econtext->ecxt_aggnulls, 0, sizeof(bool) * node->numaggs);
/* Release all temp storage */
MemoryContextReset(node->aggcontext);
if (((Agg *) node->ss.ps.plan)->aggstrategy == AGG_HASHED)
{
/* Rebuild an empty hash table */
build_hash_table(node);
node->table_filled = false;
}