# log_rotation_size

> log_rotation_size is the PostgreSQL setting that defines the maximum size a log file can reach before being rotated.
---

> [!NOTE]
> **Fact — official short description:** “Sets the maximum size a log file can reach before being rotated.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `integer` | Upstream pg_settings type |
| Context | `sighup` | Takes effect after configuration reload |
| Unit | `kB` | Raw unit |
| Range | `0` – `2147483647` | 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 | `10240` | 10 MiB |
{.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 | `10240` | `kB` | 10 MiB |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

log_rotation_size sets the maximum size a log file can reach before being rotated. 0 disables size-based creation of new log files. The collector rotates when the current file reaches approximately this size; zero disables the size trigger but not time-based rotation.

log_rotation_size 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 | Use a nonzero log_rotation_size when file size itself must be bounded, and coordinate it with a filename that cannot collide during multiple rotations in one time period. If set to zero, verify that time-based rotation and disk alerts provide the bound instead. |
| OLAP | Analytical bursts can cross a size threshold repeatedly; test the resulting filename suffixes, shipping throughput, and maximum single-file size rather than choosing a larger number by habit. |
| Small nodes | A modest size cap limits damage from a logging spike, but too-small files increase metadata and shipping overhead. Zero is acceptable only with a proven time-based cycle and free-space guardrail. |
{.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 | `0` | different | `'0'` |
| OLAP | `0` | different | `'0'` |
| CRIT | `0` | different | `'0'` |
| TINY | `0` | different | `'0'` |
{.full-width}

> [!CAUTION]
> **Advice — pending human review.** Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 = 0 (dcs); OLAP: PG9.0–19 Beta 3 = 0 (dcs); CRIT: PG9.0–19 Beta 3 = 0 (dcs); TINY: PG9.0–19 Beta 3 = 0 (dcs). Advice, pending human review — Editorial inference: Disabling size rotation appears intended to make daily time rotation the single file-cycle authority; disk safeguards still need independent verification.

## Common pitfalls {#common-pitfalls}

- Editing log_rotation_size 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.
- Setting zero without a working time-based or external rotation policy and allowing unbounded growth.

## 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/)

## References {#references}

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