# force_parallel_mode

> force_parallel_mode — Forces use of parallel query facilities. Observed in PG9.6–15; its last measured boot default is off in PG15, with user context. It was removed in PG16.
---

> [!NOTE]
> **Fact — official short description:** “Forces use of parallel query facilities.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `enum` | Upstream pg_settings type |
| Context | `user` | Settable by an ordinary user |
| Unit | — | Raw unit |
| Range | — | Raw limits in the last observed version |
| Enum values | `off`, `on`, `regress` | — for non-enum types |
| Category | Developer Options | Upstream classification |
| Latest boot value | `off` | off |
{.fields meta="-"}

## Lifecycle {#lifecycle}

| Fact | Value |
| --- | --- |
| First observed | PG9.6 |
| Present in | PG9.6–15 |
| Removed in | PG16 |
| Introduction commit | [`7c944bd90339`](https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=7c944bd903392829608a9fba5b0e68c4fe89abf8) — Introduce a new GUC force_parallel_mode for testing purposes. |
| Commit date | 2016-02-07 |
| Discussion | — |

## Default history {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG9.6–15 | `off` | — | off |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

Through PG15, force_parallel_mode forced otherwise safe queries to run under a Gather so parallel-mode behavior could be tested even without an expected speedup. regress suppressed output differences for regression suites.

It did not make unsafe queries safe and could impose parallel-context restrictions even when no worker ran. The top-level Gather was diagnostic overhead rather than a plan hint.

PostgreSQL 16 removed this GUC and introduced debug_parallel_query for the testing role. Upgrade configurations must delete the old name and should not automatically enable the replacement in production. 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 | Do not configure force_parallel_mode on current PostgreSQL. Remove it during upgrades; use any named successor only for the same controlled developer test, not as a production default. |
| OLAP | Analytical workload does not justify retaining the removed force_parallel_mode. Diagnose current versions with supported EXPLAIN, logs, or the documented replacement. |
| Small nodes | Delete force_parallel_mode from modern configurations. Unknown-parameter startup failure and diagnostic overhead outweigh any historical use. |
{.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: PG9.6–15 unmodified; OLAP: PG9.6–15 unmodified; CRIT: PG9.6–15 unmodified; TINY: PG9.6–15 unmodified. No Pigsty-specific rationale is inferred from an absent override.

## Common pitfalls {#common-pitfalls}

- Leaving force_parallel_mode enabled after the bounded diagnostic or recovery task.
- Running the experiment on the only copy of production data.
- Underestimating log, core-file, temporary-file, WAL, CPU, or connection-slot amplification.
- Treating a server that merely starts or completes a query as proof that data and behavior are correct.

## Related parameters {#related-parameters}

[`debug_parallel_query`](/parameters/debug-parallel-query/) · [`max_parallel_workers_per_gather`](/parameters/max-parallel-workers-per-gather/) · [`max_parallel_workers`](/parameters/max-parallel-workers/) · [`parallel_setup_cost`](/parameters/parallel-setup-cost/)

## References {#references}

- [PostgreSQL 15 — force_parallel_mode](https://www.postgresql.org/docs/15/runtime-config-developer.html#GUC-FORCE-PARALLEL-MODE)
- [Machine-readable GUC export](/data/guc.jsonl)