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Improve INTERSECT/EXCEPT hashing by realizing that we don't need to make any

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hashtable entries for tuples that are found only in the second input: they
can never contribute to the output.  Furthermore, this implies that the
planner should endeavor to put first the smaller (in number of groups) input
relation for an INTERSECT.  Implement that, and upgrade prepunion's estimation
of the number of rows returned by setops so that there's some amount of sanity
in the estimate of which one is smaller.
This commit is contained in:
Tom Lane
2008-08-07 19:35:02 +00:00
parent 368df30427
commit af95d7aa63
9 changed files with 278 additions and 159 deletions
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3
src/backend/nodes/outfuncs.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.332 2008/08/07 03:04:03 tgl Exp $
* $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.333 2008/08/07 19:35:02 tgl Exp $
*
* NOTES
* Every node type that can appear in stored rules' parsetrees *must*
@ -611,6 +611,7 @@ _outSetOp(StringInfo str, SetOp *node)
appendStringInfo(str, " %u", node->dupOperators[i]);
WRITE_INT_FIELD(flagColIdx);
WRITE_INT_FIELD(firstFlag);
WRITE_LONG_FIELD(numGroups);
}