# enable_presorted_aggregate

> enable_presorted_aggregate — Enables the planner's ability to produce plans that provide presorted input for ORDER BY / DISTINCT aggregate functions. Observed in PG16–19 Beta 3; its last measured boot default is on in PG19 Beta 3, with user context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.
---

> [!NOTE]
> **Fact — official short description:** “Enables the planner's ability to produce plans that provide presorted input for ORDER BY / DISTINCT aggregate functions.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `bool` | Upstream pg_settings type |
| Context | `user` | Settable by an ordinary user |
| Unit | — | Raw unit |
| Range | — | Raw limits in the last observed version |
| Enum values | — | — for non-enum types |
| Category | Query Tuning / Planner Method Configuration | Upstream classification |
| Latest boot value | `on` | on |
{.fields meta="-"}

## Lifecycle {#lifecycle}

| Fact | Value |
| --- | --- |
| First observed | PG16 |
| Present in | PG16–19 Beta 3 |
| Removed in | No |
| Introduction commit | [`3226f47282a0`](https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=3226f47282a05979483475d1e4a11aab8c1bfc39) — Add enable_presorted_aggregate GUC |
| Commit date | 2022-12-20 |
| Discussion | [thread 1](https://postgr.es/m/CAApHDvr1Sm+g9hbv4REOVuvQKeDWXcKUAhmbK5K+dfun0s9CvA@mail.gmail.com) |

## Default history {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG16–19 Beta 3 | `on` | — | on |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

enable_presorted_aggregate controls whether the planner may choose plans that deliver input already ordered for aggregate ORDER BY or DISTINCT clauses.

It is consulted while a plan is built. A session-level change is useful for comparing EXPLAIN alternatives, but an already cached plan is not retroactively rewritten; invalidation or replanning is required to observe a different choice.

The switch changes which candidate paths the planner may cost; it does not make the chosen method faster by itself. Its user context permits session- or transaction-local changes; newly performed or newly planned work sees the value.

## Tuning advice {#tuning-advice}

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

| Workload | Guidance |
| --- | --- |
| OLTP | Keep the upstream default for routine OLTP. Use a transaction- or session-local change to diagnose whether choosing plans that deliver input already ordered for aggregate ORDER BY or DISTINCT clauses explains a regression, then repair statistics, indexes, estimates, or query shape instead of leaving a cluster-wide method ban. |
| OLAP | Benchmark representative analytical plans with and without enable_presorted_aggregate. Judge planning time, memory, spill, and execution time together; a win for one report is not evidence for a global setting. |
| Small nodes | Do not use enable_presorted_aggregate as a permanent hint on a small host. Resource pressure may change the best method, so verify with EXPLAIN (ANALYZE, BUFFERS) and keep the change scoped to the affected workload if it is still needed. |
{.full-width}

## Pigsty {#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 | — | — |
{.full-width}

> [!CAUTION]
> **Advice — pending human review.** Fact from the current Pigsty template projection: OLTP: PG16–19 Beta 3 unmodified; OLAP: PG16–19 Beta 3 unmodified; CRIT: PG16–19 Beta 3 unmodified; TINY: PG16–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

## Common pitfalls {#common-pitfalls}

- Treating enable_presorted_aggregate as a query hint even though it affects every plan built in its scope.
- Testing an already cached prepared plan and concluding that the setting has no effect.
- Masking stale statistics or cardinality errors by disabling a plan method globally.
- The switch changes which candidate paths the planner may cost; it does not make the chosen method faster by itself.

## Related parameters {#related-parameters}

[`enable_sort`](/parameters/enable-sort/) · [`enable_incremental_sort`](/parameters/enable-incremental-sort/) · [`enable_group_by_reordering`](/parameters/enable-group-by-reordering/) · [`work_mem`](/parameters/work-mem/)

## References {#references}

- [PostgreSQL 19 Beta 3 — enable_presorted_aggregate](https://www.postgresql.org/docs/19/runtime-config-query.html#GUC-ENABLE-PRESORTED-AGGREGATE)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)