# log_line_prefix

> log_line_prefix is the PostgreSQL setting that controls information prefixed to each log line.
---

> [!NOTE]
> **Fact — official short description:** “Controls information prefixed to each log line.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `string` | Upstream pg_settings type |
| Context | `sighup` | Takes effect after configuration reload |
| Unit | — | Raw unit |
| Range | — | Raw limits in the last observed version |
| Enum values | — | — for non-enum types |
| Category | Reporting and Logging / What to Log | Upstream classification |
| Latest boot value | `%m [%p] ` | %m [%p]  |
{.fields meta="-"}

## Lifecycle {#lifecycle}

| Fact | Value |
| --- | --- |
| First observed | PG9.0 (research boundary) |
| Present in | PG9.0–19 Beta 3 |
| Removed in | No |
| Introduction commit | Not asserted: predates the PG9.0 research boundary |
| Commit date | — |
| Discussion | — |

## Default history {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG9.0–9.6 | `""` | — | empty string |
| PG10–19 Beta 3 | `%m [%p] ` | — | %m [%p]  |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

log_line_prefix controls information prefixed to each log line. An empty string means no prefix. Percent escapes add session, user, database, process, application, and timing context; csvlog and jsonlog already carry structured fields separately.

log_line_prefix is a SIGHUP-context setting: a configuration reload activates the new server value without a restart; subsequent operations that consult it use the refreshed value.

It changes emitted diagnostic data rather than query semantics, but volume, sensitive content, log_line_prefix, destinations, collector throughput, and retention determine operational cost and usefulness.

## Tuning advice {#tuning-advice}

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

| Workload | Guidance |
| --- | --- |
| OLTP | Tune log_line_prefix against an explicit observability question and a measured log-volume budget. Prefer selective thresholds, sampling, or role-level overrides over indiscriminate capture. |
| OLAP | Analytical jobs can justify richer log_line_prefix telemetry, but account for long statements, large bind values, and bursty completion patterns in the log pipeline. |
| Small nodes | Keep log_line_prefix useful but bounded: verify disk, collector, retention, and redaction capacity before increasing detail or frequency. |
{.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: PG9.0–19 Beta 3 unmodified; OLAP: PG9.0–19 Beta 3 unmodified; CRIT: PG9.0–19 Beta 3 unmodified; TINY: PG9.0–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

## Common pitfalls {#common-pitfalls}

- Editing log_line_prefix without reloading configuration and verifying the effective value and subsequent behavior.
- Enabling richer logging without budgeting collector throughput, storage, retention, and downstream query cost.
- Writing SQL text, bind values, identities, or host data without a redaction and access-control policy.
- Omitting process, session, database, user, or application identity needed to correlate multiline text logs.

## Related parameters {#related-parameters}

[`application_name`](/parameters/application-name/) · [`cluster_name`](/parameters/cluster-name/) · [`update_process_title`](/parameters/update-process-title/) · [`log_timezone`](/parameters/log-timezone/) · [`log_hostname`](/parameters/log-hostname/)

## References {#references}

- [PostgreSQL 19 Beta 3 — log_line_prefix](https://www.postgresql.org/docs/19/runtime-config-logging.html#GUC-LOG-LINE-PREFIX)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)