autovacuum_multixact_freeze_max_age

autovacuum_multixact_freeze_max_age — Multixact age at which to autovacuum a table to prevent multixact wraparound. Observed in PG9.3–19 Beta 3; its last measured boot default is 400000000 in PG19 Beta 3, with postmaster context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.

Note

Fact — official short description: “Multixact age at which to autovacuum a table to prevent multixact wraparound.”

Identity

Type , Valueinteger: Upstream pg_settings type
Context , Valuepostmaster: Requires a server restart
Unit , Value—: Raw unit
Range , Value10000 – 2000000000: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueVacuuming / Automatic Vacuuming: Upstream classification
Latest boot value , Value400000000: 400000000

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	`400000000`	—	400000000

How it works

Multixact age at which to autovacuum a table to prevent multixact wraparound. The value is fixed when the server starts, so changing it requires a restart.

Reaching the max age forces an aggressive autovacuum even if ordinary autovacuum is disabled; a per-table override can only lower the global ceiling. Safety must be assessed across every database/table age together with long transactions and replication slots.

Monitor and change autovacuum_multixact_freeze_max_age together with autovacuum_freeze_max_age, vacuum_freeze_min_age, vacuum_freeze_table_age. Validate on the relevant server role and real workload, then use its postmaster context to choose session change, reload, or restart; a historical boot default is not the current effective value.

Tuning advice

Tip

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

Workload	Guidance
OLTP	Calibrate autovacuum_multixact_freeze_max_age against the oldest XID/MXID age in every database and measured vacuum completion rate. Remove long transactions, stale slots, and blocked workers; never raise ages merely to hide a backlog.
OLAP	Proactively VACUUM (FREEZE) newly loaded or static partitions in batch windows and reserve I/O time for full scans. Convert age budgets using peak transaction rate, not a wall-clock guess.
Small nodes	Upstream defaults are usually safest. A small system still needs anti-wraparound maintenance; monitor every database, not only the application database.

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

Ignoring MultiXact member storage pressure, which can force work earlier.
Assuming XID-age monitoring also covers MXID age.
Raising the ceiling while long-lived row locks keep generating old multixacts.
Changing the global value while a table storage parameter overrides it.
Treating reltuples and cumulative change statistics as exact real-time counts.

autovacuum_freeze_max_age · vacuum_freeze_min_age · vacuum_freeze_table_age · vacuum_failsafe_age · vacuum_multixact_freeze_min_age · vacuum_multixact_freeze_table_age