Enables the WAL summarizer process.
At a glance
| Property | Value |
|---|---|
| Parameter | summarize_wal |
| Category | Write Ahead Log |
| Default | off |
| Value type | boolean (on/off) |
| Change scope | Reload (postgresql.conf, SIGHUP) |
| Available in | PostgreSQL 17, 18, 19 (added in 17) |
What it does
Enables the WAL summarizer process. Note that WAL summarization can be enabled either on a primary or on a standby. This parameter can only be set in the postgresql.conf file or on the server command line. The default is off.
The server cannot be started with summarize_wal=on if wal_level is set to minimal. If summarize_wal=on is configured after server startup while wal_level=minimal, the summarizer will run but refuse to generate summary files for any WAL generated with wal_level=minimal.
(Description quoted from the official PostgreSQL documentation.)
How to apply a change
Set it in postgresql.conf (or with ALTER SYSTEM) and reload with SELECT pg_reload_conf(); or pg_ctl reload — no restart needed.
Inspect the current value and source with SHOW summarize_wal; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'summarize_wal';.
Tuning guidance
Enable it to support incremental backups (it produces WAL summaries pg_basebackup uses); it adds a small background cost. Turn it on only if you actually run incremental backups.