Parameter · Vacuuming / Freezing
vacuum_multixact_freeze_min_age
Minimum age at which VACUUM should freeze a MultiXactId in a table row.
- Default:
5000000 - Type: integer
- Range: 0 … 1000000000
- Applies: Session (any user)
In plain words
The MultiXact counterpart of vacuum_freeze_min_age: when VACUUM visits a row with a MultiXact older than this (5 million), it replaces it with a plain XID or removes it, so old MultiXact storage can be discarded.
For DBAs and operators
Effective value is capped at half of autovacuum_multixact_freeze_max_age. The default (5 million) is much lower than for XIDs, so old MultiXacts are replaced early and pg_multixact can be truncated sooner. After an aggressive vacuum, mxid_age(relminmxid) drops to roughly this value. Lowering it helps tables with heavy row-locking whose pg_multixact directory keeps growing.
How to change it
Any user can change it for their session with SET.
See it in context
Related parameters
autovacuum_multixact_freeze_max_age vacuum_multixact_freeze_table_age vacuum_freeze_min_age