database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-10-27 00:12:01 +03:00
Code Activity

Make the planner estimate costs for nestloop inner indexscans on the basis

Browse Source 
that the Mackert-Lohmann formula applies across all the repetitions of the
nestloop, not just each scan independently.  We use the M-L formula to
estimate the number of pages fetched from the index as well as from the table;
that isn't what it was designed for, but it seems reasonably applicable
anyway.  This makes large numbers of repetitions look much cheaper than
before, which accords with many reports we've received of overestimation
of the cost of a nestloop.  Also, change the index access cost model to
charge random_page_cost per index leaf page touched, while explicitly
not counting anything for access to metapage or upper tree pages.  This
may all need tweaking after we get some field experience, but in simple
tests it seems to be giving saner results than before.  The main thing
is to get the infrastructure in place to let cost_index() and amcostestimate
functions take repeated scans into account at all.  Per my recent proposal.

Note: this patch changes pg_proc.h, but I did not force initdb because
the changes are basically cosmetic --- the system does not look into
pg_proc to decide how to call an index amcostestimate function, and
there's no way to call such a function from SQL at all.
This commit is contained in:
Tom Lane
2006-06-06 17:59:58 +00:00
parent 05631354f3
commit 8a30cc2127
14 changed files with 340 additions and 202 deletions
Download Patch File Download Diff File Expand all files Collapse all files

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

@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/optimizer/cost.h,v 1.75 2006/06/05 03:03:42 tgl Exp $
* $PostgreSQL: pgsql/src/include/optimizer/cost.h,v 1.76 2006/06/06 17:59:58 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -41,7 +41,7 @@ extern DLLIMPORT double random_page_cost;
extern DLLIMPORT double cpu_tuple_cost;
extern DLLIMPORT double cpu_index_tuple_cost;
extern DLLIMPORT double cpu_operator_cost;
extern double effective_cache_size;
extern DLLIMPORT double effective_cache_size;
extern Cost disable_cost;
extern bool enable_seqscan;
extern bool enable_indexscan;
@@ -55,11 +55,13 @@ extern bool enable_hashjoin;
extern bool constraint_exclusion;
extern double clamp_row_est(double nrows);
extern double index_pages_fetched(double tuples_fetched, BlockNumber pages,
BlockNumber other_pages);
extern void cost_seqscan(Path *path, PlannerInfo *root, RelOptInfo *baserel);
extern void cost_index(IndexPath *path, PlannerInfo *root, IndexOptInfo *index,
List *indexQuals, bool is_injoin);
List *indexQuals, RelOptInfo *outer_rel);
extern void cost_bitmap_heap_scan(Path *path, PlannerInfo *root, RelOptInfo *baserel,
Path *bitmapqual, bool is_injoin);
Path *bitmapqual);
extern void cost_bitmap_and_node(BitmapAndPath *path, PlannerInfo *root);
extern void cost_bitmap_or_node(BitmapOrPath *path, PlannerInfo *root);
extern void cost_bitmap_tree_node(Path *path, Cost *cost, Selectivity *selec);

4
src/include/optimizer/pathnode.h
View File

@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/optimizer/pathnode.h,v 1.67 2006/03/05 15:58:57 momjian Exp $
* $PostgreSQL: pgsql/src/include/optimizer/pathnode.h,v 1.68 2006/06/06 17:59:58 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -33,7 +33,7 @@ extern IndexPath *create_index_path(PlannerInfo *root,
List *clause_groups,
List *pathkeys,
ScanDirection indexscandir,
bool isjoininner);
RelOptInfo *outer_rel);
extern BitmapHeapPath *create_bitmap_heap_path(PlannerInfo *root,
RelOptInfo *rel,
Path *bitmapqual,

7
src/include/optimizer/paths.h
View File

@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/optimizer/paths.h,v 1.92 2006/03/05 15:58:57 momjian Exp $
* $PostgreSQL: pgsql/src/include/optimizer/paths.h,v 1.93 2006/06/06 17:59:58 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -44,10 +44,9 @@ typedef enum
extern void create_index_paths(PlannerInfo *root, RelOptInfo *rel);
extern List *generate_bitmap_or_paths(PlannerInfo *root, RelOptInfo *rel,
List *clauses, List *outer_clauses,
bool isjoininner,
Relids outer_relids);
RelOptInfo *outer_rel);
extern Path *best_inner_indexscan(PlannerInfo *root, RelOptInfo *rel,
Relids outer_relids, JoinType jointype);
RelOptInfo *outer_rel, JoinType jointype);
extern List *group_clauses_by_indexkey(IndexOptInfo *index,
List *clauses, List *outer_clauses,
Relids outer_relids,