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Change the division of labor between grouping_planner and query_planner

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so that the latter estimates the number of groups that grouping will
produce.  This is needed because it is primarily query_planner that
makes the decision between fast-start and fast-finish plans, and in the
original coding it was unable to make more than a crude rule-of-thumb
choice when the query involved grouping.  This revision helps us make
saner choices for queries like SELECT ... GROUP BY ... LIMIT, as in a
recent example from Mark Kirkwood.  Also move the responsibility for
canonicalizing sort_pathkeys and group_pathkeys into query_planner;
this information has to be available anyway to support the first change,
and doing it this way lets us get rid of compare_noncanonical_pathkeys
entirely.
This commit is contained in:
Tom Lane
2005-08-27 22:13:44 +00:00
parent 9e56c5a4cf
commit 4e5fbb34b3
7 changed files with 144 additions and 206 deletions
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5
src/include/optimizer/paths.h
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/optimizer/paths.h,v 1.86 2005/07/28 20:26:22 tgl Exp $
* $PostgreSQL: pgsql/src/include/optimizer/paths.h,v 1.87 2005/08/27 22:13:44 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -102,9 +102,6 @@ extern void generate_implied_equalities(PlannerInfo *root);
extern List *canonicalize_pathkeys(PlannerInfo *root, List *pathkeys);
extern PathKeysComparison compare_pathkeys(List *keys1, List *keys2);
extern bool pathkeys_contained_in(List *keys1, List *keys2);
extern PathKeysComparison compare_noncanonical_pathkeys(List *keys1,
List *keys2);
extern bool noncanonical_pathkeys_contained_in(List *keys1, List *keys2);
extern Path *get_cheapest_path_for_pathkeys(List *paths, List *pathkeys,
CostSelector cost_criterion);
extern Path *get_cheapest_fractional_path_for_pathkeys(List *paths,

5
src/include/optimizer/planmain.h
View File

@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/optimizer/planmain.h,v 1.87 2005/08/18 17:51:12 tgl Exp $
* $PostgreSQL: pgsql/src/include/optimizer/planmain.h,v 1.88 2005/08/27 22:13:44 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -22,7 +22,8 @@
*/
extern void query_planner(PlannerInfo *root, List *tlist,
double tuple_fraction,
Path **cheapest_path, Path **sorted_path);
Path **cheapest_path, Path **sorted_path,
double *num_groups);
/*
* prototypes for plan/planagg.c