# log_truncate_on_rotation

> log_truncate_on_rotation is the PostgreSQL setting that controls whether PostgreSQL truncates existing log files of same name during log rotation.
---

> [!NOTE]
> **Fact — official short description:** “Truncate existing log files of same name during log rotation.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `bool` | 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 / Where to Log | Upstream classification |
| Latest boot value | `off` | off |
{.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 |
| --- | --- | --- | --- |
| PG9.0–19 Beta 3 | `off` | — | off |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

log_truncate_on_rotation truncates existing log files of same name during log rotation. Truncation occurs when time-based rotation reuses an existing filename; size rotation and other causes do not apply the same overwrite rule.

log_truncate_on_rotation 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.

The active path is composed from log_destination, logging_collector or syslog/eventlog, file naming and permissions, rotation triggers, and external shipping or retention.

## Tuning advice {#tuning-advice}

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

| Workload | Guidance |
| --- | --- |
| OLTP | Enable log_truncate_on_rotation only when time-based rotation intentionally reuses a filename and the previous file has been durably shipped or is meant to be replaced. Leave it off for unique timestamped names. |
| OLAP | For analytical logs, confirm that long-running ingestion has finished before a repeating name is truncated; use unique names when completion cannot be guaranteed. |
| Small nodes | A short repeating cycle can bound disk use, but truncation is not retention management. Monitor shipping and backups so the next time rotation cannot erase the only copy. |
{.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 | `on` | different | `'on'` |
| OLAP | `on` | different | `'on'` |
| CRIT | `on` | different | `'on'` |
| TINY | `on` | different | `'on'` |
{.full-width}

> [!CAUTION]
> **Advice — pending human review.** Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 = on (dcs); OLAP: PG9.0–19 Beta 3 = on (dcs); CRIT: PG9.0–19 Beta 3 = on (dcs); TINY: PG9.0–19 Beta 3 = on (dcs). Advice, pending human review — Editorial inference: Truncation closes the weekday filename cycle so a reused daily name replaces the prior week's file instead of appending forever.

## Common pitfalls {#common-pitfalls}

- Editing log_truncate_on_rotation without reloading configuration and verifying the effective value and subsequent behavior.
- Combining incompatible destination, collector, filename, and rotation assumptions and then losing or overwriting logs.
- Failing to monitor a full or unwritable log target, which can block logging or database activity depending on the path.
- Expecting truncation on every rotation path; it is tied to time-based reuse of an existing filename.

## Related parameters {#related-parameters}

[`logging_collector`](/parameters/logging-collector/) · [`log_destination`](/parameters/log-destination/) · [`log_directory`](/parameters/log-directory/) · [`log_filename`](/parameters/log-filename/) · [`log_rotation_age`](/parameters/log-rotation-age/) · [`log_rotation_size`](/parameters/log-rotation-size/)

## References {#references}

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