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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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4
src/include/utils/lsyscache.h
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@ -6,7 +6,7 @@
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Id: lsyscache.h,v 1.39 2001/11/05 17:46:36 momjian Exp $
* $Id: lsyscache.h,v 1.40 2002/03/01 04:09:28 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -29,6 +29,8 @@ extern RegProcedure get_opcode(Oid opno);
extern char *get_opname(Oid opno);
extern bool op_mergejoinable(Oid opno, Oid ltype, Oid rtype,
Oid *leftOp, Oid *rightOp);
extern void op_mergejoin_crossops(Oid opno, Oid *ltop, Oid *gtop,
RegProcedure *ltproc, RegProcedure *gtproc);
extern Oid op_hashjoinable(Oid opno, Oid ltype, Oid rtype);
extern bool op_iscachable(Oid opno);
extern Oid get_commutator(Oid opno);