jit_profiling_support

jit_profiling_support — Register JIT-compiled functions with perf profiler. Observed in PG11–19 Beta 3; its last measured boot default is off in PG19 Beta 3, with superuser-backend context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.

Note

Fact — official short description: “Register JIT-compiled functions with perf profiler.”

Identity

Type , Valuebool: Upstream pg_settings type
Context , Valuesuperuser-backend: Fixed when a superuser backend starts
Unit , Value—: Raw unit
Range , Value—: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueDeveloper Options: Upstream classification
Latest boot value , Valueoff: off

Lifecycle

Fact	Value
First observed	PG11
Present in	PG11–19 Beta 3
Removed in	No
Introduction commit	`250bca7fc145` — Debugging and profiling support for LLVM JIT provider.
Commit date	2018-03-22
Discussion	thread 1

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG11–19 Beta 3	`off`	—	off

How it works

jit_profiling_support emits registration data so Linux perf can attribute samples to JIT-generated functions when LLVM support is available. Files are written under the server user’s ~/.debug/jit directory.

The value is fixed at backend start and does not enable JIT. It only affects queries that generate code after crossing normal JIT gates.

PostgreSQL does not clean the profiling files automatically. Long-lived or busy systems can accumulate sensitive artifacts and consume disk. Its superuser-backend context fixes the value during connection startup and restricts who may set it.

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_profiling_support. 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_profiling_support’s debug overhead and artifacts. Prefer standard EXPLAIN and statistics first, and isolate any developer experiment from normal users.
Small nodes	Keep jit_profiling_support at its upstream default. A small host has less spare CPU, disk, connection, and log capacity for developer instrumentation.

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	—	—

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

Leaving jit_profiling_support 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.

jit · jit_above_cost · jit_debugging_support · jit_dump_bitcode · data_directory