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Small performance improvement for hash joins and hash aggregation: 

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
View File

@ -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;
}

83
src/backend/executor/nodeHashjoin.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/executor/nodeHashjoin.c,v 1.50 2003/05/05 17:57:47 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/executor/nodeHashjoin.c,v 1.51 2003/05/30 20:23:10 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -56,9 +56,7 @@ ExecHashJoin(HashJoinState *node)
HashJoinTable hashtable;
HeapTuple curtuple;
TupleTableSlot *outerTupleSlot;
TupleTableSlot *innerTupleSlot;
int i;
bool hashPhaseDone;
/*
* get information from HashJoin node
@ -69,7 +67,6 @@ ExecHashJoin(HashJoinState *node)
otherqual = node->js.ps.qual;
hashNode = (HashState *) innerPlanState(node);
outerNode = outerPlanState(node);
hashPhaseDone = node->hj_hashdone;
dir = estate->es_direction;
/*
@ -114,24 +111,20 @@ ExecHashJoin(HashJoinState *node)
/*
* if this is the first call, build the hash table for inner relation
*/
if (!hashPhaseDone)
{ /* if the hash phase not completed */
if (hashtable == NULL)
{ /* if the hash table has not been created */
if (!node->hj_hashdone)
{
/*
* create the hash table
*/
Assert(hashtable == NULL);
hashtable = ExecHashTableCreate((Hash *) hashNode->ps.plan);
node->hj_HashTable = hashtable;
/*
* create the hash table
*/
hashtable = ExecHashTableCreate((Hash *) hashNode->ps.plan);
node->hj_HashTable = hashtable;
/*
* execute the Hash node, to build the hash table
*/
hashNode->hashtable = hashtable;
innerTupleSlot = ExecProcNode((PlanState *) hashNode);
}
node->hj_hashdone = true;
/*
* execute the Hash node, to build the hash table
*/
hashNode->hashtable = hashtable;
(void) ExecProcNode((PlanState *) hashNode);
/*
* Open temp files for outer batches, if needed. Note that file
@ -139,9 +132,9 @@ ExecHashJoin(HashJoinState *node)
*/
for (i = 0; i < hashtable->nbatch; i++)
hashtable->outerBatchFile[i] = BufFileCreateTemp(false);
node->hj_hashdone = true;
}
else if (hashtable == NULL)
return NULL;
/*
* Now get an outer tuple and probe into the hash table for matches
@ -159,11 +152,7 @@ ExecHashJoin(HashJoinState *node)
node);
if (TupIsNull(outerTupleSlot))
{
/*
* when the last batch runs out, clean up and exit
*/
ExecHashTableDestroy(hashtable);
node->hj_HashTable = NULL;
/* end of join */
return NULL;
}
@ -410,8 +399,8 @@ ExecInitHashJoin(HashJoin *node, EState *estate)
*/
hjstate->hj_hashdone = false;
hjstate->hj_HashTable = (HashJoinTable) NULL;
hjstate->hj_CurBucketNo = 0;
hjstate->hj_CurTuple = (HashJoinTuple) NULL;
@ -461,7 +450,7 @@ void
ExecEndHashJoin(HashJoinState *node)
{
/*
* free hash table in case we end plan before all tuples are retrieved
* Free hash table
*/
if (node->hj_HashTable)
{
@ -682,21 +671,41 @@ ExecHashJoinSaveTuple(HeapTuple heapTuple,
void
ExecReScanHashJoin(HashJoinState *node, ExprContext *exprCtxt)
{
/*
* If we haven't yet built the hash table then we can just return;
* nothing done yet, so nothing to undo.
*/
if (!node->hj_hashdone)
return;
node->hj_hashdone = false;
Assert(node->hj_HashTable != NULL);
/*
* Unfortunately, currently we have to destroy hashtable in all
* cases...
* In a multi-batch join, we currently have to do rescans the hard way,
* primarily because batch temp files may have already been released.
* But if it's a single-batch join, and there is no parameter change
* for the inner subnode, then we can just re-use the existing hash
* table without rebuilding it.
*/
if (node->hj_HashTable)
if (node->hj_HashTable->nbatch == 0 &&
((PlanState *) node)->righttree->chgParam == NULL)
{
/* okay to reuse the hash table; needn't rescan inner, either */
}
else
{
/* must destroy and rebuild hash table */
node->hj_hashdone = false;
ExecHashTableDestroy(node->hj_HashTable);
node->hj_HashTable = NULL;
/*
* if chgParam of subnode is not null then plan will be re-scanned
* by first ExecProcNode.
*/
if (((PlanState *) node)->righttree->chgParam == NULL)
ExecReScan(((PlanState *) node)->righttree, exprCtxt);
}
/* Always reset intra-tuple state */
node->hj_CurBucketNo = 0;
node->hj_CurTuple = (HashJoinTuple) NULL;
@ -706,11 +715,9 @@ ExecReScanHashJoin(HashJoinState *node, ExprContext *exprCtxt)
node->hj_MatchedOuter = false;
/*
* if chgParam of subnodes is not null then plans will be re-scanned
* if chgParam of subnode is not null then plan will be re-scanned
* by first ExecProcNode.
*/
if (((PlanState *) node)->lefttree->chgParam == NULL)
ExecReScan(((PlanState *) node)->lefttree, exprCtxt);
if (((PlanState *) node)->righttree->chgParam == NULL)
ExecReScan(((PlanState *) node)->righttree, exprCtxt);
}