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Optimize multi-batch hash joins when the outer relation has a nonuniform

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distribution, by creating a special fast path for the (first few) most common
values of the outer relation.  Tuples having hashvalues matching the MCVs
are effectively forced to be in the first batch, so that we never write
them out to the batch temp files.

Bryce Cutt and Ramon Lawrence, with some editorialization by me.
This commit is contained in:
Tom Lane
2009-03-21 00:04:40 +00:00
parent 249d936bed
commit 596efd27ed
10 changed files with 604 additions and 34 deletions
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8
src/include/executor/nodeHash.h
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/executor/nodeHash.h,v 1.46 2009/01/01 17:23:59 momjian Exp $
* $PostgreSQL: pgsql/src/include/executor/nodeHash.h,v 1.47 2009/03/21 00:04:40 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -41,8 +41,10 @@ extern void ExecHashGetBucketAndBatch(HashJoinTable hashtable,
extern HashJoinTuple ExecScanHashBucket(HashJoinState *hjstate,
ExprContext *econtext);
extern void ExecHashTableReset(HashJoinTable hashtable);
extern void ExecChooseHashTableSize(double ntuples, int tupwidth,
extern void ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
int *numbuckets,
int *numbatches);
int *numbatches,
int *num_skew_mcvs);
extern int ExecHashGetSkewBucket(HashJoinTable hashtable, uint32 hashvalue);
#endif /* NODEHASH_H */