https://github.com/postgrespro/plantuner
https://github.com/postgrespro/plantuner
Last synced: 6 days ago
JSON representation
- Host: GitHub
- URL: https://github.com/postgrespro/plantuner
- Owner: postgrespro
- License: other
- Created: 2018-05-23T11:42:51.000Z (almost 7 years ago)
- Default Branch: master
- Last Pushed: 2021-02-12T11:57:02.000Z (about 4 years ago)
- Last Synced: 2025-04-24T10:48:42.975Z (7 days ago)
- Language: C
- Size: 14.6 KB
- Stars: 9
- Watchers: 30
- Forks: 4
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
[](https://travis-ci.org/postgrespro/plantuner)
[](https://raw.githubusercontent.com/postgrespro/jsquery/master/LICENSE)
# Plantuner - enable planner hints
`plantuner` is a contribution module for PostgreSQL 9.5+, which
enable planner hints.
All work was done by Teodor Sigaev ([email protected]) and Oleg Bartunov
([email protected]).
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 the latest source code.
export USE_PGXS=1
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)
```