plantuner

Plantuner - enable planner hints

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.

Installation

  • Get latest source of plantuner from CVS Repository
  • gmake && gmake install && gmake installcheck

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.forbid_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.forbid_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)