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Lock Management

Complete dossiers for 5 core PostgreSQL settings in Lock Management.

Dossier URLs remain flat; this category exists only to organize browsing and the sidebar.

1 - deadlock_timeout

deadlock_timeout — Sets the time to wait on a lock before checking for deadlock. Observed in PG9.0–19 Beta 3; its last measured boot default is 1 s in PG19 Beta 3, with superuser context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.
Note

Fact — official short description: “Sets the time to wait on a lock before checking for deadlock.”

Identity

Type Valueinteger
Upstream pg_settings type
Context Valuesuperuser
Settable at runtime by a superuser
Unit Valuems
Raw unit
Range Value1 – 2147483647
Raw limits in the last observed version
Enum values Value—
— for non-enum types
Category ValueLock Management
Upstream classification
Latest boot value Value1000
1 s

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
PG9.0–19 Beta 3 1000 ms 1 s

How it works

Sets the time to wait on a lock before checking for deadlock. A superuser or a role granted SET privilege can change it for the relevant session or configuration scope.

PostgreSQL waits this long before running the comparatively expensive deadlock detector. The same interval controls lock-wait logging when log_lock_waits is enabled, so lowering it improves diagnostics and deadlock response at the cost of more checks during ordinary contention.

Monitor and change deadlock_timeout together with log_lock_waits, lock_timeout, max_locks_per_transaction. Validate on the relevant server role and real workload, then use its superuser 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 deadlock_timeout 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 50ms different 50ms
OLAP 50ms different 50ms
CRIT 50ms different 50ms
TINY 50ms different 50ms
Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 = 50ms (dcs); OLAP: PG9.0–19 Beta 3 = 50ms (dcs); CRIT: PG9.0–19 Beta 3 = 50ms (dcs); TINY: PG9.0–19 Beta 3 = 50ms (dcs). Advice, pending human review — Editorial interpretation, pending human maintainer review: the override appears intended to detect true deadlocks and emit lock-wait diagnostics faster than upstream; confirm it against the current Pigsty templates, hardware fixture, and operational guarantees before publication.

Common pitfalls

  • Reading an average shared-memory sizing value as a hard per-transaction limit.
  • Raising it without the multiplier from connections and prepared transactions.
  • Expanding lock memory instead of fixing long transactions, access order, or partition explosion.
  • Ignoring compatible startup lock capacity on standbys.

Related parameters

log_lock_waits · lock_timeout · max_locks_per_transaction · max_pred_locks_per_transaction · max_pred_locks_per_page · max_pred_locks_per_relation

References

2 - 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.

Related parameters

deadlock_timeout · log_lock_waits · lock_timeout · max_pred_locks_per_transaction · max_pred_locks_per_relation · max_pred_locks_per_page

References

3 - max_pred_locks_per_page

max_pred_locks_per_page — Sets the maximum number of predicate-locked tuples per page. Observed in PG10–19 Beta 3; its last measured boot default is 2 in PG19 Beta 3, with sighup context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.
Note

Fact — official short description: “Sets the maximum number of predicate-locked tuples per page.”

Identity

Type Valueinteger
Upstream pg_settings type
Context Valuesighup
Takes effect after configuration reload
Unit Value—
Raw unit
Range Value0 – 2147483647
Raw limits in the last observed version
Enum values Value—
— for non-enum types
Category ValueLock Management
Upstream classification
Latest boot value Value2
2

Lifecycle

Fact Value
First observed PG10
Present in PG10–19 Beta 3
Removed in No
Introduction commit c63172d60f24 — Add GUCs for predicate lock promotion thresholds.
Commit date 2017-04-07
Discussion —

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions Raw boot_val Unit Human value
PG10–19 Beta 3 2 — 2

How it works

Sets the maximum number of predicate-locked tuples per page. A configuration reload applies a new value; existing work already in flight is not retroactively changed.

Serializable Snapshot Isolation promotes tuple-level predicate locks to a page-level lock after this many tuples on one page. Promotion saves shared memory but increases the chance that unrelated writes appear to conflict and cause serialization failures.

Monitor and change max_pred_locks_per_page together with max_pred_locks_per_transaction, max_pred_locks_per_relation, default_transaction_isolation. Validate on the relevant server role and real workload, then use its sighup 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_pred_locks_per_page 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 Unmodified — —
OLAP Unmodified — —
CRIT Unmodified — —
TINY Unmodified — —
Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG10–19 Beta 3 unmodified; OLAP: PG10–19 Beta 3 unmodified; CRIT: PG10–19 Beta 3 unmodified; TINY: PG10–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

  • Reading an average shared-memory sizing value as a hard per-transaction limit.
  • Raising it without the multiplier from connections and prepared transactions.
  • Expanding lock memory instead of fixing long transactions, access order, or partition explosion.
  • Ignoring compatible startup lock capacity on standbys.

Related parameters

max_pred_locks_per_transaction · max_pred_locks_per_relation · default_transaction_isolation · max_locks_per_transaction · deadlock_timeout

References

4 - max_pred_locks_per_relation

max_pred_locks_per_relation — Sets the maximum number of predicate-locked pages and tuples per relation. Observed in PG10–19 Beta 3; its last measured boot default is -2 in PG19 Beta 3, with sighup context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.
Note

Fact — official short description: “Sets the maximum number of predicate-locked pages and tuples per relation.”

Identity

Type Valueinteger
Upstream pg_settings type
Context Valuesighup
Takes effect after configuration reload
Unit Value—
Raw unit
Range Value-2147483648 – 2147483647
Raw limits in the last observed version
Enum values Value—
— for non-enum types
Category ValueLock Management
Upstream classification
Latest boot value Value-2
-2

Lifecycle

Fact Value
First observed PG10
Present in PG10–19 Beta 3
Removed in No
Introduction commit c63172d60f24 — Add GUCs for predicate lock promotion thresholds.
Commit date 2017-04-07
Discussion —

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions Raw boot_val Unit Human value
PG10–19 Beta 3 -2 — -2

How it works

Sets the maximum number of predicate-locked pages and tuples per relation. A configuration reload applies a new value; existing work already in flight is not retroactively changed.

SSI promotes page/tuple predicate locks to one relation-level lock at this threshold. A negative value means max_pred_locks_per_transaction divided by its absolute value; promotion changes granularity, not SQL lock strength.

Monitor and change max_pred_locks_per_relation together with max_pred_locks_per_transaction, max_pred_locks_per_page, default_transaction_isolation. Validate on the relevant server role and real workload, then use its sighup 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_pred_locks_per_relation 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 Unmodified — —
OLAP Unmodified — —
CRIT Unmodified — —
TINY Unmodified — —
Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG10–19 Beta 3 unmodified; OLAP: PG10–19 Beta 3 unmodified; CRIT: PG10–19 Beta 3 unmodified; TINY: PG10–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

  • Reading an average shared-memory sizing value as a hard per-transaction limit.
  • Raising it without the multiplier from connections and prepared transactions.
  • Expanding lock memory instead of fixing long transactions, access order, or partition explosion.
  • Ignoring compatible startup lock capacity on standbys.

Related parameters

max_pred_locks_per_transaction · max_pred_locks_per_page · default_transaction_isolation · max_locks_per_transaction · deadlock_timeout

References

5 - max_pred_locks_per_transaction

max_pred_locks_per_transaction — Sets the maximum number of predicate locks per transaction. Observed in PG9.1–19 Beta 3; its last measured boot default is 64 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 predicate 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 Value64
64

Lifecycle

Fact Value
First observed PG9.1
Present in PG9.1–19 Beta 3
Removed in No
Introduction commit 6a77e9385eb4 — Rename max_predicate_locks_per_transaction.
Commit date 2011-02-15
Discussion —

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions Raw boot_val Unit Human value
PG9.1–19 Beta 3 64 — 64

How it works

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

This sizes the shared predicate-lock table per backend or prepared transaction for SERIALIZABLE conflict tracking. It is an average shared-memory allocation rather than a hard per-transaction ceiling, and is unrelated to ordinary row-lock counts.

Monitor and change max_pred_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_pred_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 Unmodified — —
OLAP Unmodified — —
CRIT Unmodified — —
TINY Unmodified — —
Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG9.1–19 Beta 3 unmodified; OLAP: PG9.1–19 Beta 3 unmodified; CRIT: PG9.1–19 Beta 3 unmodified; TINY: PG9.1–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

  • Reading an average shared-memory sizing value as a hard per-transaction limit.
  • Raising it without the multiplier from connections and prepared transactions.
  • Expanding lock memory instead of fixing long transactions, access order, or partition explosion.
  • Ignoring compatible startup lock capacity on standbys.

Related parameters

deadlock_timeout · log_lock_waits · lock_timeout · max_locks_per_transaction · max_pred_locks_per_relation · max_pred_locks_per_page

References