custom_variable_classes

custom_variable_classes — Sets the list of known custom variable classes. Observed in PG9.0–9.1; its last measured boot default is not set in PG9.1, with sighup context. It was removed in PG9.2.

Note

Fact — official short description: “Sets the list of known custom variable classes.”

Identity

Type , Valuestring: Upstream pg_settings type
Context , Valuesighup: Takes effect after configuration reload
Unit , Value—: Raw unit
Range , Value—: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueCustomized Options: Upstream classification
Latest boot value , Value—: not set

Lifecycle

Fact	Value
First observed	PG9.0 (research boundary)
Present in	PG9.0–9.1
Removed in	PG9.2
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
PG9.0–9.1	—	—	not set

How it works

PostgreSQL describes custom_variable_classes as follows: “Sets the list of known custom variable classes.” A configuration reload applies the value to the server without a full restart. The atlas measures it in PG9.0–9.1; boot_val is the compiled or initialized baseline, not proof of a running cluster’s effective setting.

Old releases required extensions and applications to predeclare accepted custom GUC prefixes. PostgreSQL 9.2 removed that registration mechanism; modern servers accept any two-part custom name and preserve an unrecognized placeholder until the defining extension is loaded.

Read it together with shared_preload_libraries, session_preload_libraries, config_file, allow_alter_system. Check SHOW and pg_settings on the target server, verify the source and pending_restart fields, and compare workload, logs, and resource metrics before and after any change.

Tuning advice

Tip

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

Workload	Guidance
OLTP	Do not add this retired name to a current OLTP configuration. Translate its intent to the documented successor, test the migration under connection and write concurrency, and remove stale automation that still emits it.
OLAP	For an upgrade or analytical estate, inventory every generated configuration before cutover. Map the old control to its successor and compare plans, throughput, WAL, or logging behavior rather than assuming the old numeric value is portable.
Small nodes	Delete the obsolete override after recording why it existed. On a small node, prefer the successor’s default until measurements justify a new value; an unknown startup parameter can otherwise stop the server.

Pigsty

Values use the fixed 8-vCPU, 32-GiB, 100-GiB SSD fixture and render the current Pigsty templates for PG9.1; 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: PG9.0–9.1 unmodified; OLAP: PG9.0–9.1 unmodified; CRIT: PG9.0–9.1 unmodified; TINY: PG9.0–9.1 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Treating the measured boot_val for custom_variable_classes as proof of the effective value on an initialized or managed cluster.
Applying a change as though it were immediate while pg_settings reports sighup context.
Changing this setting in isolation without checking the linked limits, observability, and rollback path.
Copying the removed name into a modern postgresql.conf instead of migrating to its documented successor.

shared_preload_libraries · session_preload_libraries · config_file · allow_alter_system