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Teach planner about the idea that a mergejoin won't necessarily read

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both input streams to the end.  If one variable's range is much less
than the other, an indexscan-based merge can win by not scanning all
of the other table.  Per example from Reinhard Max.
This commit is contained in:
Tom Lane
2002-03-01 04:09:28 +00:00
parent fdc60bd9d9
commit f8c109528c
6 changed files with 422 additions and 113 deletions
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72
src/backend/utils/cache/lsyscache.c vendored
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@ -7,7 +7,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/utils/cache/lsyscache.c,v 1.59 2001/10/25 05:49:46 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/utils/cache/lsyscache.c,v 1.60 2002/03/01 04:09:26 tgl Exp $
*
* NOTES
* Eventually, the index information should go through here, too.
@ -369,6 +369,76 @@ op_mergejoinable(Oid opno, Oid ltype, Oid rtype, Oid *leftOp, Oid *rightOp)
return result;
}
/*
* op_mergejoin_crossops
*
* Returns the cross-type comparison operators (ltype "<" rtype and
* ltype ">" rtype) for an operator previously determined to be
* mergejoinable. Optionally, fetches the regproc ids of these
* operators, as well as their operator OIDs.
*
* Raises error if operators cannot be found. Assuming that the operator
* had indeed been marked mergejoinable, this indicates that whoever marked
* it so was mistaken.
*/
void
op_mergejoin_crossops(Oid opno, Oid *ltop, Oid *gtop,
RegProcedure *ltproc, RegProcedure *gtproc)
{
HeapTuple tp;
Form_pg_operator optup;
Oid oprleft,
oprright;
/*
* Get the declared left and right operand types of the operator.
*/
tp = SearchSysCache(OPEROID,
ObjectIdGetDatum(opno),
0, 0, 0);
if (!HeapTupleIsValid(tp)) /* shouldn't happen */
elog(ERROR, "op_mergejoin_crossops: operator %u not found", opno);
optup = (Form_pg_operator) GETSTRUCT(tp);
oprleft = optup->oprleft;
oprright = optup->oprright;
ReleaseSysCache(tp);
/*
* Look up the "<" operator with the same input types. If there isn't
* one, whoever marked the "=" operator mergejoinable was a loser.
*/
tp = SearchSysCache(OPERNAME,
PointerGetDatum("<"),
ObjectIdGetDatum(oprleft),
ObjectIdGetDatum(oprright),
CharGetDatum('b'));
if (!HeapTupleIsValid(tp))
elog(ERROR, "op_mergejoin_crossops: mergejoin operator %u has no matching < operator",
opno);
optup = (Form_pg_operator) GETSTRUCT(tp);
*ltop = tp->t_data->t_oid;
if (ltproc)
*ltproc = optup->oprcode;
ReleaseSysCache(tp);
/*
* And the same for the ">" operator.
*/
tp = SearchSysCache(OPERNAME,
PointerGetDatum(">"),
ObjectIdGetDatum(oprleft),
ObjectIdGetDatum(oprright),
CharGetDatum('b'));
if (!HeapTupleIsValid(tp))
elog(ERROR, "op_mergejoin_crossops: mergejoin operator %u has no matching > operator",
opno);
optup = (Form_pg_operator) GETSTRUCT(tp);
*gtop = tp->t_data->t_oid;
if (gtproc)
*gtproc = optup->oprcode;
ReleaseSysCache(tp);
}
/*
* op_hashjoinable
*