Heroku PGSettings

Last updated April 28, 2023

Heroku Postgres non-legacy Standard, Premium, Private, and Shield plans can manage database settings by configuring parameters via the pg:settings command.

$ heroku pg:settings postgresql-large-1234 -a example-app
=== postgresql-large-1234
log-lock-waits:                     true
log-min-duration-statement:         2000
log-statement:                      ddl
track-functions:                    pl
auto-explain:                       true
auto-explain.log-analyze:           false
auto-explain.log-buffers:           false
auto-explain.log-min-duration:      200
auto-explain.log-nested-statements: false
auto-explain.log-triggers:          false
auto-explain.log-verbose:           false

Essential-tier plans include the default settings, which you can’t reconfigure.

log-lock-waits

log-lock-waits determines whether a log message is produced when a session waits longer than 1 second to acquire a lock. Lock waits can cause performance issues. The default value in Heroku Postgres is on.

$ heroku pg:settings:log-lock-waits off -a example-app
log-lock-waits has been set to false for postgresql-large-1234.
When a deadlock is detected, no log message will be emitted in your application's logs.

log-min-duration-statement

log-min-duration-statement logs the duration of each completed statement if the statement ran for at least the specified number of milliseconds. A value of 0 logs everything and a value of -1 disables logging. This setting can help you track down unoptimized queries in your applications. The default value of log-min-duration-statement in Heroku Postgres is set to 2000 milliseconds (2 seconds).

In a system with hundreds of queries executing every second, log files can grow quickly and hamper database performance.

$ heroku pg:settings:log-min-duration-statement 3000 postgresql-large-1234 -a example-app
log-min-duration-statement has been set to 3000 for postgresql-large-1234.

log-statement

log-statement controls which normal SQL statements are logged. This setting can help you debug complex queries or review queries made by your app or any database user. Valid values for log-statement are:

  • none: Stops logging normal queries. Other logs are still generated such as slow query logs, queries waiting in locks, and syntax errors
  • ddl: All data definition statements, such as CREATE, ALTER, and DROP are logged
  • mod: Includes all statements from ddl as well as data-modifying statements such as INSERT, UPDATE, DELETE, TRUNCATE, and COPY
  • all: All statements are logged

The default value of log-statement in Heroku Postgres is ddl.

$ heroku pg:settings:log-statement all postgresql-large-1234 -a example-app
log-statement has been set to all for postgresql-large-1234.

track-functions

track-functions determines which functions have their execution statistics tracked. These statistics can be found in the pg_stat_user_functions view. Valid values for track-functions are:

  • none: No function statistics are recorded. This value is the default.
  • pl: Procedural language function statistics are recorded (for example, PL/pgSQL functions).
  • all: All functions, including SQL and C language function statics are recorded.
$ heroku pg:settings:track-functions pl postgresql-large-1234 -a example-app
track-functions has been set to pl for postgresql-large-1234.
Track only procedural-language functions.

auto-explain

auto_explain logs query execution plans automatically without having to run EXPLAIN by hand. Running auto-explain can help identify queries that run slowly and can help you understand how to optimize your database’s performance. Enable auto_explain with:

$ heroku pg:settings:auto-explain on -a example-app

Enabling auto_explain can cause performance impacts and a significant increase in log volume so use with caution and monitor your database performance. auto-explain enables the module for all future Heroku Postgres connections. Existing connections must be reestablished before auto_explain logging occurs.

auto-explain:log_min_duration

log-min-duration configures a minimum log duration in milliseconds. Setting a log duration of -1 disables all logging, while setting a log duration of 0 logs all executed queries. The default value is -1.

$ heroku pg:settings:auto-explain:log-min-duration 200 -a example-app

auto-explain:log-analyze

log-analyze runs EXPLAIN ANALYZE on all queries regardless if they’re logged or not. This setting can have a significant performance impact on your database so use with caution. The default value is off.

$ heroku pg:settings:auto-explain:log-analyze on -a example-app

auto-explain:log-buffers

log-buffers is equivalent to calling EXPLAIN BUFFERS and can only be used with pg:settings:auto-explain:log-analyze turned on. The default value is off.

$ heroku pg:settings:auto-explain:log-buffers on -a example-app

auto-explain:log-nested-statements

log-nested-statements adds nested statements to the execution plan’s log. The default value is off.

$ heroku pg:settings:auto-explain:log-nested-statements on -a example-app

auto-explain:log-triggers

log-triggers includes trigger execution statistics in the execution plan’s logs. The default value is off.

$ heroku pg:settings:auto-explain:log-triggers on -a example-app

auto-explain:log-verbose

log-verbose includes verbose details in the execution plan’s logs. This setting is equivalent to running EXPLAIN VERBOSE. The default value is off.

$ heroku pg:settings:auto-explain:log-verbose on -a example-app

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