vacuum_multixact_freeze_min_age

vacuum_multixact_freeze_min_age — Minimum age at which VACUUM should freeze a MultiXactId in a table row. Observed in PG9.3–19 Beta 3; its last measured boot default is 5000000 in PG19 Beta 3, with user context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.

Note

Fact — official short description: “Minimum age at which VACUUM should freeze a MultiXactId in a table row.”

Identity

Type , Valueinteger: Upstream pg_settings type
Context , Valueuser: Settable by an ordinary user
Unit , Value—: Raw unit
Range , Value0 – 1000000000: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueVacuuming / Freezing: Upstream classification
Latest boot value , Value5000000: 5000000

Lifecycle

Fact	Value
First observed	PG9.3
Present in	PG9.3–19 Beta 3
Removed in	No
Introduction commit	`fb47de2be6e4` — Separate multixact freezing parameters from xid’s
Commit date	2014-02-13
Discussion	—

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG9.3–19 Beta 3	`5000000`	—	5000000

How it works

Sets the minimum MultiXact age at which VACUUM replaces old tuple xmax MultiXact IDs. It is a user-context setting and is distinct from the XID cutoff.

Lower values make VACUUM process MXIDs earlier; higher values defer that work. PostgreSQL may still remove MultiXacts proactively, and the effective cutoff is capped at half of autovacuum_multixact_freeze_max_age.

Track mxid_age(relminmxid), mxid_age(datminmxid), and pg_multixact member storage. Interpret it with vacuum_multixact_freeze_table_age, autovacuum_multixact_freeze_max_age, and vacuum_multixact_failsafe_age.

Tuning advice

Tip

Advice. These are workload-specific starting points and must be validated with measurements.

Workload	Guidance
OLTP	Tune from MXID consumption caused by row locks and multitransaction workloads. Preserve ample distance to autovacuum_multixact_freeze_max_age and monitor member storage as well as age.
OLAP	Bulk reads alone rarely justify a change, but concurrent row-locking loaders can consume MXIDs quickly. Measure mxid_age and pg_multixact growth during the real load.
Small nodes	Keep the default unless MXID evidence says otherwise. Low transaction volume does not protect a workload that creates many shared row locks.

Pigsty

Values use the fixed 8-vCPU, 32-GiB, 100-GiB SSD fixture and render the current Pigsty templates for PG19 Beta 3; this does not assert current Pigsty support for that historical or beta release.

Template	Effective value	Versus upstream boot	Source expression
OLTP	Unmodified	—	—
OLAP	Unmodified	—	—
CRIT	Unmodified	—	—
TINY	Unmodified	—	—

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG9.3–19 Beta 3 unmodified; OLAP: PG9.3–19 Beta 3 unmodified; CRIT: PG9.3–19 Beta 3 unmodified; TINY: PG9.3–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Describing the cutoff as an XID control or monitoring only relfrozenxid.
Ignoring pg_multixact member-space pressure, which can force aggressive work before the configured age.
Raising the value while long-lived shared row locks continue to generate old MXIDs.
Using autovacuum_freeze_max_age instead of the MultiXact-specific maximum when calculating the cap.

autovacuum_multixact_freeze_max_age · vacuum_multixact_freeze_table_age · vacuum_multixact_failsafe_age · vacuum_freeze_min_age · autovacuum · log_autovacuum_min_duration