lc_ctype

lc_ctype — Shows the character classification and case conversion locale. Observed in PG9.0–15; its last measured boot default is C in PG15, with internal context. It was removed in PG16.

Note

Fact — official short description: “Shows the character classification and case conversion locale.”

Identity

Type , Valuestring: Upstream pg_settings type
Context , Valueinternal: Internal/preset and not user-settable
Unit , Value—: Raw unit
Range , Value—: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValuePreset Options: Upstream classification
Latest boot value , ValueC: C

Lifecycle

Fact	Value
First observed	PG9.0 (research boundary)
Present in	PG9.0–15
Removed in	PG16
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
PG9.0–15	`C`	—	C

How it works

Reported the current database’s character-classification and case-conversion locale through PG15. It was internal/read-only and PostgreSQL 16 removed it from pg_settings.

The locale is fixed when a database is created and can differ by database. It affects locale-aware character classes and case conversion, but is not a session switch and cannot be changed with ALTER SYSTEM.

On PG16 and later, migrate SHOW/current_setting consumers to pg_database locale-provider metadata and inspect pg_collation for object-level behavior. Application tests should cover case conversion and pattern/character-class assumptions.

Tuning advice

Tip

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

Workload	Guidance
OLTP	Not tunable. Migrate readers to pg_database and test case-folding, upper/lower behavior, and expression indexes before a locale/provider upgrade.
OLAP	Record locale metadata with ETL outputs whose classification or normalization depends on it. Changing the locale requires deliberate migration, not a runtime setting.
Small nodes	Keep locale choice explicit at database creation and in rebuild automation. Do not assume the host default is stable across images or operating-system upgrades.

Pigsty

Values use the fixed 8-vCPU, 32-GiB, 100-GiB SSD fixture and render the current Pigsty templates for PG15; 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: PG9.0–15 unmodified; OLAP: PG9.0–15 unmodified; CRIT: PG9.0–15 unmodified; TINY: PG9.0–15 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Trying to configure a value that was always internal/read-only.
Assuming character classification is identical across databases or locale providers.
Changing locale libraries without testing expression indexes and case-conversion results.
Migrating only monitoring text while leaving applications dependent on SHOW lc_ctype.

lc_collate · server_encoding · client_encoding · icu_validation_level · default_text_search_config · server_version_num