# synchronous_commit

> synchronous_commit — Sets the current transaction's synchronization level. Observed in PG9.0–19 Beta 3; its last measured boot default is on in PG19 Beta 3, with user context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.
---

> [!NOTE]
> **Fact — official short description:** “Sets the current transaction's synchronization level.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `enum` | Upstream pg_settings type |
| Context | `user` | Settable by an ordinary user |
| Unit | — | Raw unit |
| Range | — | Raw limits in the last observed version |
| Enum values | `local`, `remote_write`, `remote_apply`, `on`, `off` | — for non-enum types |
| Category | Write-Ahead Log / Settings | Upstream classification |
| Latest boot value | `on` | on |
{.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 | `on` | — | on |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

All modes except off wait for the transaction's WAL to be flushed locally. With off, success can be returned before local durable flush; a crash can lose recent acknowledged transactions, but recovery remains transactionally consistent and does not introduce the corruption risk associated with fsync = off.

When synchronous_standby_names selects synchronous standbys, remote_write waits for receipt and an operating-system write on a standby, on waits for a durable standby flush, and remote_apply waits for replay and query visibility. local waits only for local durable flush. Without a selected synchronous standby, the remote modes add no remote guarantee.

The effective mode is the value in force when a transaction commits. Applications can use SET LOCAL for one transaction, allowing critical and replaceable work to use different durability policies on the same server.

## Tuning advice {#tuning-advice}

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

| Workload | Guidance |
| --- | --- |
| OLTP | Keep on as the general default. Use off only for explicitly replaceable transactions, and use remote_apply only when post-commit reads on a synchronous standby require causal visibility; include network round-trip and standby health in the latency budget. |
| OLAP | For a reproducible bulk load, transaction-local off can improve throughput if losing the final unflushed portion is acceptable and the load can be rerun. Keep catalog changes, handoff markers, and externally visible completion records synchronous. |
| Small nodes | Retain on. Small systems rarely gain enough from a global durability downgrade to justify the operational ambiguity; tune individual noncritical jobs instead. |
{.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}

- Equating synchronous_commit = off with fsync = off; the former risks recent data loss, not structural corruption.
- Expecting remote_write, on, or remote_apply to wait remotely when no synchronous standby is selected.
- Using remote_write while assuming the standby is durable across an operating-system crash.
- Allowing an unavailable synchronous standby to stall commits without an HA response plan.
- Leaking a session-level SET through a connection pool instead of using SET LOCAL or reset discipline.

## Related parameters {#related-parameters}

[`synchronous_standby_names`](/parameters/synchronous-standby-names/) · [`fsync`](/parameters/fsync/) · [`wal_writer_delay`](/parameters/wal-writer-delay/) · [`wal_sync_method`](/parameters/wal-sync-method/) · [`commit_delay`](/parameters/commit-delay/) · [`wal_level`](/parameters/wal-level/)

## References {#references}

- [PostgreSQL 19 Beta 3 — synchronous_commit](https://www.postgresql.org/docs/19/runtime-config-wal.html#GUC-SYNCHRONOUS-COMMIT)
- [PostgreSQL 18: Asynchronous Commit](https://www.postgresql.org/docs/18/wal-async-commit.html)
- [PostgreSQL 18: Synchronous Replication](https://www.postgresql.org/docs/18/warm-standby.html#SYNCHRONOUS-REPLICATION)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)