# wal_level

> wal_level — Sets the level of information written to the WAL. Observed in PG9.0–19 Beta 3; its last measured boot default is replica in PG19 Beta 3, with postmaster context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.
---

> [!NOTE]
> **Fact — official short description:** “Sets the level of information written to the WAL.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `enum` | Upstream pg_settings type |
| Context | `postmaster` | Requires a server restart |
| Unit | — | Raw unit |
| Range | — | Raw limits in the last observed version |
| Enum values | `minimal`, `replica`, `logical` | — for non-enum types |
| Category | Write-Ahead Log / Settings | Upstream classification |
| Latest boot value | `replica` | replica |
{.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 | `minimal` | — | minimal |
| PG10–19 Beta 3 | `replica` | — | replica |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

Sets the level of information written to the WAL. The value is fixed when the server starts, so changing it requires a restart.

minimal logs only crash-recovery needs and is incompatible with archiving/streaming modes that require replica data; replica supports physical replication and archive recovery; logical adds logical-decoding information. Changing level requires restart and may change WAL volume.

Monitor and change wal_level together with wal_compression, full_page_writes, wal_log_hints. Validate on the relevant server role and real workload, then use its postmaster context to choose session change, reload, or restart; a historical boot default is not the current effective value.

## Tuning advice {#tuning-advice}

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

| Workload | Guidance |
| --- | --- |
| OLTP | Establish durability and recovery objectives first, then tune wal_level from WAL rate, flush latency, checkpoints, and peak pg_wal usage. Validate every change with crash/recovery and archive monitoring. |
| OLAP | Provision WAL, archive bandwidth, and recovery I/O for bulk-load peaks. Coordinate load pacing and checkpoints when reducing spikes; never break the recovery chain for throughput. |
| Small nodes | Start from safe defaults or the measured Pigsty value and set explicit alerts for limited disk capacity. Do not disable durability or break the recovery chain merely to save modest I/O. |
{.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 | `logical` | different | `logical` |
| OLAP | `logical` | different | `logical` |
| CRIT | `logical` | different | `logical` |
| TINY | `logical` | different | `logical` |
{.full-width}

> [!CAUTION]
> **Advice — pending human review.** Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 = logical (dcs); OLAP: PG9.0–19 Beta 3 = logical (dcs); CRIT: PG9.0–19 Beta 3 = logical (dcs); TINY: PG9.0–19 Beta 3 = logical (dcs). Advice, pending human review — Editorial interpretation, pending human maintainer review: the override appears intended to enable logical decoding by default across Pigsty profiles; confirm it against the current Pigsty templates, hardware fixture, and operational guarantees before publication.

## Common pitfalls {#common-pitfalls}

- Selecting minimal while expecting archiving, streaming replication, or logical decoding.
- Raising it without budgeting extra WAL and restart downtime.
- Lowering it while slots/subscriptions still depend on the higher level.
- Confusing pg_settings base units with human-readable configuration units.
- Benchmarking throughput without a crash-recovery and archive-restore test.

## Related parameters {#related-parameters}

[`wal_compression`](/parameters/wal-compression/) · [`full_page_writes`](/parameters/full-page-writes/) · [`wal_log_hints`](/parameters/wal-log-hints/) · [`wal_buffers`](/parameters/wal-buffers/) · [`max_wal_senders`](/parameters/max-wal-senders/) · [`max_replication_slots`](/parameters/max-replication-slots/)

## References {#references}

- [PostgreSQL 19 Beta 3 — wal_level](https://www.postgresql.org/docs/19/runtime-config-wal.html#GUC-WAL-LEVEL)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)