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Take OUTER JOIN semantics into account when estimating the size of join

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relations.  It's not very bright, but at least it now knows that
A LEFT JOIN B must produce at least as many rows as are in A ...
This commit is contained in:
Tom Lane 2001-02-16 00:03:08 +00:00
parent ca71c66190
commit b29f68f611
5 changed files with 47 additions and 11 deletions
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35
src/backend/optimizer/path/costsize.c
View File

@ -41,7 +41,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.67 2001/02/15 17:46:40 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.68 2001/02/16 00:03:07 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -837,11 +837,12 @@ void
set_joinrel_size_estimates(Query *root, RelOptInfo *rel,
RelOptInfo *outer_rel,
RelOptInfo *inner_rel,
JoinType jointype,
List *restrictlist)
{
double temp;
/* cartesian product */
/* Start with the Cartesian product */
temp = outer_rel->rows * inner_rel->rows;
/*
@ -854,6 +855,35 @@ set_joinrel_size_estimates(Query *root, RelOptInfo *rel,
restrictlist,
0);
/*
* If we are doing an outer join, take that into account: the output
* must be at least as large as the non-nullable input. (Is there any
* chance of being even smarter?)
*/
switch (jointype)
{
case JOIN_INNER:
break;
case JOIN_LEFT:
if (temp < outer_rel->rows)
temp = outer_rel->rows;
break;
case JOIN_RIGHT:
if (temp < inner_rel->rows)
temp = inner_rel->rows;
break;
case JOIN_FULL:
if (temp < outer_rel->rows)
temp = outer_rel->rows;
if (temp < inner_rel->rows)
temp = inner_rel->rows;
break;
default:
elog(ERROR, "set_joinrel_size_estimates: unsupported join type %d",
(int) jointype);
break;
}
/*
* Force estimate to be at least one row, to make explain output look
* better and to avoid possible divide-by-zero when interpolating
@ -861,6 +891,7 @@ set_joinrel_size_estimates(Query *root, RelOptInfo *rel,
*/
if (temp < 1.0)
temp = 1.0;
rel->rows = temp;
/*

4
src/backend/optimizer/path/joinrels.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinrels.c,v 1.50 2001/01/24 19:42:58 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinrels.c,v 1.51 2001/02/16 00:03:07 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -394,7 +394,7 @@ make_join_rel(Query *root, RelOptInfo *rel1, RelOptInfo *rel2,
* Find or build the join RelOptInfo, and compute the restrictlist
* that goes with this particular joining.
*/
joinrel = get_join_rel(root, rel1, rel2, &restrictlist);
joinrel = get_join_rel(root, rel1, rel2, jointype, &restrictlist);
/*
* Consider paths using each rel as both outer and inner.

6
src/backend/optimizer/util/relnode.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/relnode.c,v 1.31 2001/01/24 19:43:00 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/relnode.c,v 1.32 2001/02/16 00:03:08 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -152,6 +152,7 @@ find_join_rel(Query *root, Relids relids)
*
* 'outer_rel' and 'inner_rel' are relation nodes for the relations to be
* joined
* 'jointype': type of join (inner/outer)
* 'restrictlist_ptr': result variable. If not NULL, *restrictlist_ptr
* receives the list of RestrictInfo nodes that apply to this
* particular pair of joinable relations.
@ -163,6 +164,7 @@ RelOptInfo *
get_join_rel(Query *root,
RelOptInfo *outer_rel,
RelOptInfo *inner_rel,
JoinType jointype,
List **restrictlist_ptr)
{
List *joinrelids;
@ -252,7 +254,7 @@ get_join_rel(Query *root,
* Set estimates of the joinrel's size.
*/
set_joinrel_size_estimates(root, joinrel, outer_rel, inner_rel,
restrictlist);
jointype, restrictlist);
/*
* Add the joinrel to the query's joinrel list.

3
src/include/optimizer/cost.h
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Id: cost.h,v 1.37 2001/01/24 19:43:26 momjian Exp $
* $Id: cost.h,v 1.38 2001/02/16 00:03:05 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -70,6 +70,7 @@ extern void set_baserel_size_estimates(Query *root, RelOptInfo *rel);
extern void set_joinrel_size_estimates(Query *root, RelOptInfo *rel,
RelOptInfo *outer_rel,
RelOptInfo *inner_rel,
JoinType jointype,
List *restrictlist);
/*

10
src/include/optimizer/pathnode.h
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Id: pathnode.h,v 1.33 2001/01/24 19:43:26 momjian Exp $
* $Id: pathnode.h,v 1.34 2001/02/16 00:03:06 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -66,8 +66,10 @@ extern HashPath *create_hashjoin_path(RelOptInfo *joinrel,
*/
extern RelOptInfo *get_base_rel(Query *root, int relid);
extern RelOptInfo *make_base_rel(Query *root, int relid);
extern RelOptInfo *get_join_rel(Query *root, RelOptInfo *outer_rel,
RelOptInfo *inner_rel,
List **restrictlist_ptr);
extern RelOptInfo *get_join_rel(Query *root,
RelOptInfo *outer_rel,
RelOptInfo *inner_rel,
JoinType jointype,
List **restrictlist_ptr);
#endif /* PATHNODE_H */