Specifies the cutoff age (in multixacts) that VACUUM should use to decide whether to trigger freezing of pages with an older multixact ID.
At a glance
| Property | Value |
|---|---|
| Parameter | vacuum_multixact_freeze_min_age |
| Category | Vacuuming |
| Default | 5 |
| Value type | integer |
| Change scope | Per-session (SET) |
| Available in | PostgreSQL 12, 13, 14, 15, 16, 17, 18, 19 (added in 12) |
What it does
Specifies the cutoff age (in multixacts) that VACUUM should use to decide whether to trigger freezing of pages with an older multixact ID. The default is 5 million multixacts. Although users can set this value anywhere from zero to one billion, VACUUM will silently limit the effective value to half the value of autovacuum_multixact_freeze_max_age, so that there is not an unreasonably short time between forced autovacuums. For more information see vacuum_for_multixact_wraparound.
(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 vacuum_multixact_freeze_min_age; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'vacuum_multixact_freeze_min_age';.
Tuning guidance
The multixact analogue of vacuum_freeze_min_age; lower it on workloads heavy in row-level locking / shared FKs that burn multixact IDs quickly.