# jit_dump_bitcode

> jit_dump_bitcode — Write out LLVM bitcode to facilitate JIT debugging. Observed in PG11–19 Beta 3; its last measured boot default is off in PG19 Beta 3, with superuser context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.
---

> [!NOTE]
> **Fact — official short description:** “Write out LLVM bitcode to facilitate JIT debugging.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `bool` | Upstream pg_settings type |
| Context | `superuser` | Settable at runtime by a superuser |
| Unit | — | Raw unit |
| Range | — | Raw limits in the last observed version |
| Enum values | — | — for non-enum types |
| Category | Developer Options | 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 | [`b96d550eb03c`](https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=b96d550eb03cfdb000def70912ec840dbe7f67da) — Support for optimizing and emitting code in LLVM JIT provider. |
| Commit date | 2018-03-22 |
| Discussion | [thread 1](https://postgr.es/m/20170901064131.tazjxwus3k2w3ybh@alap3.anarazel.de) |

## 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}

jit_dump_bitcode writes generated LLVM IR/bitcode files inside data_directory for queries that actually run JIT. It exists to inspect and reproduce JIT compiler behavior.

It does not activate JIT and produces nothing when no query crosses the JIT gates. Generated artifacts can accumulate, consume disk, and contain details derived from executed expressions.

Only a tightly controlled debugging session should enable it; files require explicit collection and cleanup. Its superuser context permits an authorized session change without a server restart.

## Tuning advice {#tuning-advice}

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

| Workload | Guidance |
| --- | --- |
| OLTP | Do not tune production OLTP with jit_dump_bitcode. Enable it only for a bounded reproduction with an owner, log/disk budget, rollback condition, and evidence-capture plan; restore the default immediately afterward. |
| OLAP | Long analytical runs can amplify jit_dump_bitcode's debug overhead and artifacts. Prefer standard EXPLAIN and statistics first, and isolate any developer experiment from normal users. |
| Small nodes | Keep jit_dump_bitcode at its upstream default. A small host has less spare CPU, disk, connection, and log capacity for developer instrumentation. |
{.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: PG11–19 Beta 3 unmodified; OLAP: PG11–19 Beta 3 unmodified; CRIT: PG11–19 Beta 3 unmodified; TINY: PG11–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

## Common pitfalls {#common-pitfalls}

- Leaving jit_dump_bitcode 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}

[`jit`](/parameters/jit/) · [`jit_above_cost`](/parameters/jit-above-cost/) · [`jit_debugging_support`](/parameters/jit-debugging-support/) · [`jit_profiling_support`](/parameters/jit-profiling-support/) · [`data_directory`](/parameters/data-directory/)

## References {#references}

- [PostgreSQL 19 Beta 3 — jit_dump_bitcode](https://www.postgresql.org/docs/19/runtime-config-developer.html#GUC-JIT-DUMP-BITCODE)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)