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New cost model for planning, incorporating a penalty for random page

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accesses versus sequential accesses, a (very crude) estimate of the
effects of caching on random page accesses, and cost to evaluate WHERE-
clause expressions.  Export critical parameters for this model as SET
variables.  Also, create SET variables for the planner's enable flags
(enable_seqscan, enable_indexscan, etc) so that these can be controlled
more conveniently than via PGOPTIONS.

Planner now estimates both startup cost (cost before retrieving
first tuple) and total cost of each path, so it can optimize queries
with LIMIT on a reasonable basis by interpolating between these costs.
Same facility is a win for EXISTS(...) subqueries and some other cases.

Redesign pathkey representation to achieve a major speedup in planning
(I saw as much as 5X on a 10-way join); also minor changes in planner
to reduce memory consumption by recycling discarded Path nodes and
not constructing unnecessary lists.

Minor cleanups to display more-plausible costs in some cases in
EXPLAIN output.

Initdb forced by change in interface to index cost estimation
functions.
This commit is contained in:
Tom Lane
2000-02-15 20:49:31 +00:00
parent 553b5da6a1
commit b1577a7c78
50 changed files with 3200 additions and 1723 deletions
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13
src/include/optimizer/pathnode.h
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2000, PostgreSQL, Inc
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Id: pathnode.h,v 1.25 2000/02/07 04:41:04 tgl Exp $
* $Id: pathnode.h,v 1.26 2000/02/15 20:49:26 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -19,15 +19,18 @@
/*
* prototypes for pathnode.c
*/
extern bool path_is_cheaper(Path *path1, Path *path2);
extern Path *set_cheapest(RelOptInfo *parent_rel, List *pathlist);
extern int compare_path_costs(Path *path1, Path *path2,
CostSelector criterion);
extern int compare_fractional_path_costs(Path *path1, Path *path2,
double fraction);
extern void set_cheapest(RelOptInfo *parent_rel);
extern void add_path(RelOptInfo *parent_rel, Path *new_path);
extern void add_pathlist(RelOptInfo *parent_rel, List *new_paths);
extern Path *create_seqscan_path(RelOptInfo *rel);
extern IndexPath *create_index_path(Query *root, RelOptInfo *rel,
IndexOptInfo *index,
List *restriction_clauses);
List *restriction_clauses,
ScanDirection indexscandir);
extern TidPath *create_tidscan_path(RelOptInfo *rel, List *tideval);
extern NestPath *create_nestloop_path(RelOptInfo *joinrel,