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pg_show_plans

pg_show_plans is a module which shows the query plans of all currently running SQL statements.

You can select the output format of plans: TEXT or JSON.

This module supports PostgreSQL versions from 9.5 to 14.

Note

When the server starts, pg_show_plans makes a hashtable on the shared-memory in order to temporarily store query plans. The hashtable size cannot be changed, so the plans are not stored if the hashtable is full.

Version

Version 1.0

Installation

You can install it to do the usual way shown below.

$ tar xvfj postgresql-13.0.tar.bz2
$ cd postgresql-13.0/contrib
$ git clone https://github.com/cybertec-postgresql/pg_show_plans.git
$ cd pg_show_plans
$ make && make install

You must add the line shown below in your postgresql.conf.

shared_preload_libraries = 'pg_show_plans'

After starting your server, you must issue CREATE EXTENSION statement shown below.

testdb=# CREATE EXTENSION pg_show_plans;

How to use

By issuing the following query, it shows the query plan and related information of the currently running SQL statements.

testdb=# SELECT * FROM pg_show_plans;
  pid  | level | userid | dbid  |                                 plan                                  
-------+-------+--------+-------+-----------------------------------------------------------------------
 11473 |     0 |     10 | 16384 | Function Scan on pg_show_plans  (cost=0.00..10.00 rows=1000 width=56)
 11504 |     0 |     10 | 16384 | Function Scan on print_item  (cost=0.25..10.25 rows=1000 width=524)
 11504 |     1 |     10 | 16384 | Result  (cost=0.00..0.01 rows=1 width=4)
(3 rows)

If you need the query plans of running SQL statements and also the corresponding query string, you issue the following query which is combined with pg_show_plans and pg_stat_activity.

testdb=# \x
Expanded display is on.
testdb=# SELECT p.pid, p.level, p.plan, a.query FROM pg_show_plans p 
   LEFT JOIN pg_stat_activity a
   ON p.pid = a.pid AND p.level = 0 ORDER BY p.pid, p.level;
-[ RECORD 1 ]-----------------------------------------------------------------------------------------
pid   | 11473
level | 0
plan  | Sort  (cost=72.08..74.58 rows=1000 width=80)                                                  +
      |   Sort Key: pg_show_plans.pid, pg_show_plans.level                                            +
      |   ->  Hash Left Join  (cost=2.25..22.25 rows=1000 width=80)                                   +
      |         Hash Cond: (pg_show_plans.pid = s.pid)                                                +
      |         Join Filter: (pg_show_plans.level = 0)                                                +
      |         ->  Function Scan on pg_show_plans  (cost=0.00..10.00 rows=1000 width=48)             +
      |         ->  Hash  (cost=1.00..1.00 rows=100 width=44)                                         +
      |               ->  Function Scan on pg_stat_get_activity s  (cost=0.00..1.00 rows=100 width=44)
query | SELECT p.pid, p.level, p.plan, a.query FROM pg_show_plans p                                   +
      |    LEFT JOIN pg_stat_activity a                                                               +
      |    ON p.pid = a.pid AND p.level = 0 ORDER BY p.pid, p.level;
-[ RECORD 2 ]-----------------------------------------------------------------------------------------
pid   | 11517
level | 0
plan  | Function Scan on print_item  (cost=0.25..10.25 rows=1000 width=524)
query | SELECT * FROM print_item(1,20);
-[ RECORD 3 ]-----------------------------------------------------------------------------------------
pid   | 11517
level | 1
plan  | Result  (cost=0.00..0.01 rows=1 width=4)
query | 

pg_show_plans View

  • pid: the pid of the process which the query is running.
  • level: the level of the query which runs the query. Top level is 0. For example, if you execute a simple select query, the level of this query's plan is 0. If you execute a function that invokes a select query, level 0 is the plan of the function and level 1 is the plan of the select query invoked by the function.
  • userid: the userid of the user which runs the query.
  • dbid: the database id of the database which the query is running.
  • plan: the query plan of the running query.

Functions

  • pg_show_plans_disable() disables the feature. Only superuser can execute it.
  • pg_show_plans_enable() enables the feature. Only superuser can execute it.
  • pgsp_format_json() changes the output format to json. Note that the format of the plans that are stored in the memory before executing this function cannot be changed.
  • pgsp_format_text() changes the output format to text. Note that the format of the plans that are stored in the memory before executing this function cannot be changed.

Configuration Parameters

  • pg_show_plans.plan_format : It controls the output format of query plans. It can be selected either text or json. Default is text.
  • pg_show_plans.max_plan_length : It sets the maximum length of query plans. Default is 16384 [byte]. Note that this parameter must be set to an integer. Note that pg_show plans allocates approximately (max_plan_length * max_connecions) bytes on the shared memory to store plans, Therefore, if the value of max_plan_length is too large, PostgreSQL may not start due to an out of memory error.
  • pg_show_plans.enable : It controls whether this feature is enabled or not in each user. Default is 'true'.

Change Log

  • 22 Mar, 2022: Version 1.0 Released.
  • 22 Mar, 2022: Improved memory utilization efficiency and obsoleted a parameter:pg_show_plans.enable_txid.
  • 30 Aug, 2021: Added a parameter:pg_show_plans.enable_txid.
  • 4 Feb, 2021: Added a parameter:pg_show_plans.enable.
  • 19 Oct, 2020: Confirmed this can be run on PostgreSQL 13.0.
  • 10 Apr, 2020: Version 1.0 RC3 Released. Supported Streaming Replication. This extension can be run on the standby server since this version.
  • 26 Mar, 2020: Version 1.0 RC2 Released. Added pgsp_format_json() and pgsp_format_text(); deleted the parameter show_level.
  • 21 Dec, 2019: Version 1.0 RC Released. Supported versions from 9.1 to 9.4.
  • 16 Aug, 2019: Version 0.8 Released. Supported the parameter:max_plan_length.
  • 12 Aug, 2019: Version 0.3 Released. Supported garbage collection.
  • 9 Aug, 2019: Version 0.2 Released. Supported nested queries.
  • 8 Aug, 2019: Version 0.1 Released.