max_locks_per_transaction

max_locks_per_transaction — Sets the maximum number of locks per transaction. Observed in PG9.0–19 Beta 3; its last measured boot default is 128 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: “Sets the maximum number of locks per transaction.”

Identity

Type , Valueinteger: Upstream pg_settings type
Context , Valuepostmaster: Requires a server restart
Unit , Value—: Raw unit
Range , Value10 – 2147483647: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueLock Management: Upstream classification
Latest boot value , Value128: 128

Lifecycle

Fact	Value
First observed	PG9.0 (research boundary)
Present in	PG9.0–19 Beta 3
Removed in	No
Introduction commit	Not asserted: predates the PG9.0 research boundary
Commit date	—
Discussion	—

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG9.0–18	`64`	—	64
PG19 Beta 3	`128`	—	128

How it works

Sets the maximum number of locks per transaction. The value is fixed when the server starts, so changing it requires a restart.

The shared lock table is sized for this average number of distinct lockable objects per backend or prepared transaction. A single transaction may exceed the number if space remains; it does not limit row locks, and standbys need a value at least as large as the primary.

Monitor and change max_locks_per_transaction together with deadlock_timeout, log_lock_waits, lock_timeout. 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 max_locks_per_transaction from lock-wait logs, objects touched, and the concurrency bound. Fix long transactions and access ordering before adding shared memory or changing detection granularity.
OLAP	Partitioned queries, bulk DDL, and SERIALIZABLE reports may touch many objects; test the worst plan, not only an average transaction.
Small nodes	Defaults are usually sufficient. If raising a startup lock-table setting, account for max_connections, prepared transactions, and standby consistency together.

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	`500`	different	`{{ pg_max_locks_per_transaction }}`
OLAP	`1000`	different	`{{ pg_max_locks_per_transaction }}`
CRIT	`500`	different	`{{ pg_max_locks_per_transaction }}`
TINY	`250`	different	`{{ pg_max_locks_per_transaction }}`

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 = 500 (dcs); OLAP: PG9.0–19 Beta 3 = 1000 (dcs); CRIT: PG9.0–19 Beta 3 = 500 (dcs); TINY: PG9.0–19 Beta 3 = 250 (dcs). Advice, pending human review — Editorial interpretation, pending human maintainer review: the override appears intended to reserve shared lock-table capacity for partition-heavy and schema-rich workloads; confirm it against the current Pigsty templates, hardware fixture, and operational guarantees before publication.

Common pitfalls

Reading it as a row-lock limit or a hard limit for one transaction.
Raising it without accounting for max_connections and prepared transactions.
Setting a standby below its primary and preventing standby queries.
Reading an average shared-memory sizing value as a hard per-transaction limit.
Raising it without the multiplier from connections and prepared transactions.

deadlock_timeout · log_lock_waits · lock_timeout · max_pred_locks_per_transaction · max_pred_locks_per_relation · max_pred_locks_per_page