-plantuner module provides plantuner.forbid_index GUC which contains comma-separated
-list of indexes forbidden to use in query.
+Plantuner - enable planner hints
-USAGE (see sql/plantuner.sql:
-% LOAD 'plantuner';
-% SET plantuner.forbid_index="i_idx, j_idx";
-% SET enable_seqscan=off;
-% explain SELECT * FROM wow;
- QUERY PLAN
---------------------------------------------------------------------------
- Seq Scan on wow (cost=10000000000.00..10000000031.40 rows=2140 width=8)
+ contrib/plantuner is a contribution module for PostgreSQL 8.4+, which
+ enable planner hints.
+ All work was done by Teodor Sigaev (teodor@sigaev.ru) and Oleg Bartunov
+ (oleg@sai.msu.su).
+
+ Sponsor: Nomao project (http://www.nomao.com)
+
+Motivation
+
+ Whether somebody think it's bad or not, but sometime it's very
+ interesting to be able to control planner (provide hints, which tells
+ optimizer to ignore its algorithm in part), which is currently
+ impossible in POstgreSQL. Oracle, for example, has over 120 hints, SQL
+ Server also provides hints.
+
+ This first version of plantuner provides a possibility to hide
+ specified indexes from PostgreSQL planner, so it will not use them.
+
+ There are many situation, when developer want to temporarily disable
+ specific index(es), without dropping them, or to instruct planner to
+ use specific index.
+
+ Next, for some workload PostgreSQL could be too pessimistic for
+ newly created tables and assumes much more rows in table than
+ it actually has. If plantuner.fix_empty_table GUC variable is set
+ to true then module will set to zero number of pages/tuples of
+ table which hasn't blocks in file.
+
+Installation
+
+ * Get latest source of plantuner from CVS Repository
+ * gmake && gmake install && gmake installcheck
+
+Syntax
+ plantuner.forbid_index (deprecated)
+ plantuner.disable_index
+ List of indexes invisible to planner
+ plantuner.enable_index
+ List of indexes visible to planner even they are hided
+ by plantuner.disable_index.
+
+Usage
+
+ To enable the module you can either load shared library 'plantuner' in
+ psql session or specify 'shared_preload_libraries' option in
+ postgresql.conf.
+=# LOAD 'plantuner';
+=# create table test(id int);
+=# create index id_idx on test(id);
+=# create index id_idx2 on test(id);
+=# \d test
+ Table "public.test"
+ Column | Type | Modifiers
+--------+---------+-----------
+ id | integer |
+Indexes:
+ "id_idx" btree (id)
+ "id_idx2" btree (id)
+=# explain select id from test where id=1;
+ QUERY PLAN
+-----------------------------------------------------------------------
+ Bitmap Heap Scan on test (cost=4.34..15.03 rows=12 width=4)
+ Recheck Cond: (id = 1)
+ -> Bitmap Index Scan on id_idx2 (cost=0.00..4.34 rows=12 width=0)
+ Index Cond: (id = 1)
+(4 rows)
+=# set enable_seqscan=off;
+=# set plantuner.disable_index='id_idx2';
+=# explain select id from test where id=1;
+ QUERY PLAN
+----------------------------------------------------------------------
+ Bitmap Heap Scan on test (cost=4.34..15.03 rows=12 width=4)
+ Recheck Cond: (id = 1)
+ -> Bitmap Index Scan on id_idx (cost=0.00..4.34 rows=12 width=0)
+ Index Cond: (id = 1)
+(4 rows)
+=# set plantuner.disable_index='id_idx2,id_idx';
+=# explain select id from test where id=1;
+ QUERY PLAN
+-------------------------------------------------------------------------
+ Seq Scan on test (cost=10000000000.00..10000000040.00 rows=12 width=4)
+ Filter: (id = 1)
+(2 rows)
+=# set plantuner.enable_index='id_idx';
+=# explain select id from test where id=1;
+ QUERY PLAN
+-----------------------------------------------------------------------
+ Bitmap Heap Scan on test (cost=4.34..15.03 rows=12 width=4)
+ Recheck Cond: (id = 1)
+ -> Bitmap Index Scan on id_idx (cost=0.00..4.34 rows=12 width=0)
+ Index Cond: (id = 1)
+(4 rows)
-It's recommended to load library by shared_preload_libraries option
-in postgresql.conf
projects / plantuner.git / blobdiff