# lc_collate

> lc_collate — Shows the collation order 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 collation order locale.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `string` | Upstream pg_settings type |
| Context | `internal` | Internal/preset and not user-settable |
| Unit | — | Raw unit |
| Range | — | Raw limits in the last observed version |
| Enum values | — | — for non-enum types |
| Category | Preset Options | Upstream classification |
| Latest boot value | `C` | C |
{.fields meta="-"}

## Lifecycle {#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 {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG9.0–15 | `C` | — | C |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

Reported the current database’s collation locale through PG15. It was an internal read-only value, not a configurable GUC, and PostgreSQL 16 removed it from pg_settings.

The collation locale is selected when a database is created and can differ between databases in one cluster. It affects ordering and comparison semantics; changing the server configuration cannot rewrite existing indexes or database locale metadata.

On PG16 and later, monitoring and applications should read the current database row in pg_database and its locale-provider-specific metadata, and use pg_collation for individual collation objects. Test collation-version changes separately from this removed reporter.

## Tuning advice {#tuning-advice}

> [!TIP]
> **Advice.** These are workload-specific starting points and must be validated with measurements.

| Workload | Guidance |
| --- | --- |
| OLTP | Not tunable. Replace SHOW/current_setting readers with a version-aware pg_database query, and regression-test indexed ordering and uniqueness when moving databases between locale providers or versions. |
| OLAP | Record per-database provider and locale beside analytical exports. A desired collation change requires a deliberate database/object migration and possible REINDEX, not a GUC edit. |
| Small nodes | Use the database-creation default only when it is intentional. Preserve locale metadata in inventory and backups so a rebuild does not silently choose different ordering rules. |
{.full-width}

## Pigsty {#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 | — | — |
{.full-width}

> [!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 {#common-pitfalls}

- Trying to remove or set lc_collate in configuration even though it was always internal/read-only.
- Assuming one cluster-wide value applies to every database.
- Changing operating-system or ICU locale data without checking collation versions and rebuilding affected indexes.
- Comparing text behavior across providers using only a locale name.

## Related parameters {#related-parameters}

[`lc_ctype`](/parameters/lc-ctype/) · [`server_encoding`](/parameters/server-encoding/) · [`client_encoding`](/parameters/client-encoding/) · [`icu_validation_level`](/parameters/icu-validation-level/) · [`default_text_search_config`](/parameters/default-text-search-config/) · [`server_version_num`](/parameters/server-version-num/)

## References {#references}

- [PostgreSQL 15 — lc_collate](https://www.postgresql.org/docs/15/runtime-config-preset.html#GUC-LC-COLLATE)
- [Machine-readable GUC export](/data/guc.jsonl)