When logging to syslog is enabled, this parameter determines how messages are delivered to syslog.
At a glance
| Property | Value |
|---|---|
| Parameter | syslog_split_messages |
| Category | Error Reporting and Logging |
| Default | (see documentation) |
| Value type | boolean (on/off) |
| Change scope | Per-session (SET) |
| Available in | PostgreSQL 12, 13, 14, 15, 16, 17, 18, 19 (added in 12) |
What it does
When logging to syslog is enabled, this parameter determines how messages are delivered to syslog. When on (the default), messages are split by lines, and long lines are split so that they will fit into 1024 bytes, which is a typical size limit for traditional syslog implementations. When off, PostgreSQL server log messages are delivered to the syslog service as is, and it is up to the syslog service to cope with the potentially bulky messages.
If syslog is ultimately logging to a text file, then the effect will be the same either way, and it is best to leave the setting on, since most syslog implementations either cannot handle large messages or would need to be specially configured to handle them. But if syslog is ultimately writing into some other medium, it might be necessary or more useful to keep messages logically together.
(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 syslog_split_messages; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'syslog_split_messages';.
Tuning guidance
Tune this for observability versus log volume, not for raw performance. More verbose logging helps diagnose problems but costs disk and I/O; quieter logging saves space but hides detail. Pick a level your log pipeline can store and search, and raise verbosity temporarily when investigating an incident.