# enable_partitionwise_aggregate

> enable_partitionwise_aggregate — Enables partitionwise aggregation and grouping. Observed in PG11–19 Beta 3; its last measured boot default is off 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 partitionwise aggregation and grouping.”

## 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 | `off` | off |
{.fields meta="-"}

## Lifecycle {#lifecycle}

| Fact | Value |
| --- | --- |
| First observed | PG11 |
| Present in | PG11–19 Beta 3 |
| Removed in | No |
| Introduction commit | [`e2f1eb0ee30d`](https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=e2f1eb0ee30d144628ab523432320f174a2c8966) — Implement partition-wise grouping/aggregation. |
| Commit date | 2018-03-22 |
| Discussion | [thread 1](https://postgr.es/m/CAM2+6=V64_xhstVHie0Rz=KPEQnLJMZt_e314P0jaT_oJ9MR8A@mail.gmail.com) |

## Default history {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG11–19 Beta 3 | `off` | — | off |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

enable_partitionwise_aggregate controls whether the planner may choose per-partition grouping or aggregation, with later finalization when grouping keys do not contain partition keys.

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.

It can multiply work_mem-limited nodes and planning effort roughly with the number of participating partitions. 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 per-partition grouping or aggregation, with later finalization when grouping keys do not contain partition keys 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_partitionwise_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_partitionwise_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 | `on` | different | `'on'` |
| CRIT | Unmodified | — | — |
| TINY | Unmodified | — | — |
{.full-width}

> [!CAUTION]
> **Advice — pending human review.** Fact from the current Pigsty template projection: OLTP: PG11–19 Beta 3 unmodified; OLAP: PG11–19 Beta 3 = on (dcs); CRIT: PG11–19 Beta 3 unmodified; TINY: PG11–19 Beta 3 unmodified. Advice, pending human review — Editorial inference, pending maintainer review: The OLAP-only override is intended to exploit partition-local aggregation for analytical schemas while avoiding its planning and memory multiplication in other profiles.

## Common pitfalls {#common-pitfalls}

- Treating enable_partitionwise_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.
- It can multiply work_mem-limited nodes and planning effort roughly with the number of participating partitions.

## Related parameters {#related-parameters}

[`enable_partitionwise_join`](/parameters/enable-partitionwise-join/) · [`enable_partition_pruning`](/parameters/enable-partition-pruning/) · [`work_mem`](/parameters/work-mem/) · [`enable_hashagg`](/parameters/enable-hashagg/) · [`max_parallel_workers_per_gather`](/parameters/max-parallel-workers-per-gather/)

## References {#references}

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