# 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 {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `integer` | Upstream pg_settings type |
| Context | `user` | Settable by an ordinary user |
| Unit | — | Raw unit |
| Range | `0` – `1000000000` | Raw limits in the last observed version |
| Enum values | — | — for non-enum types |
| Category | Vacuuming / Freezing | Upstream classification |
| Latest boot value | `5000000` | 5000000 |
{.fields meta="-"}

## Lifecycle {#lifecycle}

| Fact | Value |
| --- | --- |
| First observed | PG9.3 |
| Present in | PG9.3–19 Beta 3 |
| Removed in | No |
| Introduction commit | [`fb47de2be6e4`](https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=fb47de2be6e44397ab40508729606697f52702ac) — Separate multixact freezing parameters from xid's |
| Commit date | 2014-02-13 |
| Discussion | — |

## Default history {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG9.3–19 Beta 3 | `5000000` | — | 5000000 |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

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 {#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. |
{.full-width}

## Pigsty {#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 | — | — |
{.full-width}

> [!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 {#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.

## Related parameters {#related-parameters}

[`autovacuum_multixact_freeze_max_age`](/parameters/autovacuum-multixact-freeze-max-age/) · [`vacuum_multixact_freeze_table_age`](/parameters/vacuum-multixact-freeze-table-age/) · [`vacuum_multixact_failsafe_age`](/parameters/vacuum-multixact-failsafe-age/) · [`vacuum_freeze_min_age`](/parameters/vacuum-freeze-min-age/) · [`autovacuum`](/parameters/autovacuum/) · [`log_autovacuum_min_duration`](/parameters/log-autovacuum-min-duration/)

## References {#references}

- [PostgreSQL 19 Beta 3 — vacuum_multixact_freeze_min_age](https://www.postgresql.org/docs/19/runtime-config-vacuum.html#GUC-VACUUM-MULTIXACT-FREEZE-MIN-AGE)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)