wal_log_hints — PostgreSQL configuration parameter

When this parameter is on, the PostgreSQL server writes the entire content of each disk page to WAL during the first modification of that page after a checkpoint, even for non-critical modifications of so-called hint bits.

At a glance

What it does

When this parameter is on, the PostgreSQL server writes the entire content of each disk page to WAL during the first modification of that page after a checkpoint, even for non-critical modifications of so-called hint bits.

If data checksums are enabled, hint bit updates are always WAL-logged and this setting is ignored. You can use this setting to test how much extra WAL-logging would occur if your database had data checksums enabled.

(Description quoted from the official PostgreSQL documentation.)

How to apply a change

Can be set per session with SET, per role/database with ALTER ROLE/DATABASE ... SET, or globally in postgresql.conf.

Inspect the current value and source with SHOW wal_log_hints; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'wal_log_hints';.

Tuning guidance

Turning it on (required for pg_rewind) increases WAL volume because the first change to a page after a checkpoint is fully logged. Enable it if you need pg_rewind or use data checksums; otherwise leave it off.

Reference

PostgreSQL documentation — wal_log_hints.