# logical_decoding_work_mem

> logical_decoding_work_mem — Sets the maximum memory to be used for logical decoding. Observed in PG13–19 Beta 3; its last measured boot default is 64 MiB 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 maximum memory to be used for logical decoding.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `integer` | Upstream pg_settings type |
| Context | `user` | Settable by an ordinary user |
| Unit | `kB` | Raw unit |
| Range | `64` – `2147483647` | Raw limits in the last observed version |
| Enum values | — | — for non-enum types |
| Category | Resource Usage / Memory | Upstream classification |
| Latest boot value | `65536` | 64 MiB |
{.fields meta="-"}

## Lifecycle {#lifecycle}

| Fact | Value |
| --- | --- |
| First observed | PG13 |
| Present in | PG13–19 Beta 3 |
| Removed in | No |
| Introduction commit | [`cec2edfa7859`](https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=cec2edfa7859279f36d2374770ca920c59c73dd8) — Add logical_decoding_work_mem to limit ReorderBuffer memory usage. |
| Commit date | 2019-11-16 |
| Discussion | [thread 1](https://postgr.es/m/688b0b7f-2f6c-d827-c27b-216a8e3ea700@2ndquadrant.com) |

## Default history {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG13–19 Beta 3 | `65536` | `kB` | 64 MiB |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

logical_decoding_work_mem is the real memory threshold for one logical decoding stream before decoded changes are written to local temporary files. It is independent of ordinary query work_mem.

Each replication connection uses one such buffer, and concurrency is bounded by replication sender capacity rather than client sessions. Large in-progress transactions can spill and later be reread.

Raising the threshold can reduce serialization I/O for logical replication, but the cluster memory budget must multiply it by concurrent decoding streams and include output-plugin memory outside this accounting. Its user context permits session- or transaction-local changes; newly performed or newly planned work sees the value.

## Tuning advice {#tuning-advice}

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

| Workload | Guidance |
| --- | --- |
| OLTP | Change logical_decoding_work_mem only after identifying the corresponding resource bottleneck under concurrency. Budget total memory, I/O, disk, or kernel capacity rather than optimizing one process in isolation. |
| OLAP | Benchmark logical_decoding_work_mem with representative bulk and scan phases. Include sustained throughput, spill/writeback, and interference with other sessions, not only one operation's elapsed time. |
| Small nodes | Keep logical_decoding_work_mem conservative on a small host and prefer the upstream default when evidence is weak. A setting copied from a large server can consume a disproportionate share of resources. |
{.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: PG13–19 Beta 3 unmodified; OLAP: PG13–19 Beta 3 unmodified; CRIT: PG13–19 Beta 3 unmodified; TINY: PG13–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

## Common pitfalls {#common-pitfalls}

- Changing logical_decoding_work_mem without applying its documented unit and configuration context.
- Optimizing an isolated benchmark while ignoring concurrent aggregate resource use.
- Assuming a configured value guarantees operating-system or storage behavior.
- Failing to retest startup, failover, and workload latency after the change.

## Related parameters {#related-parameters}

[`work_mem`](/parameters/work-mem/) · [`max_wal_senders`](/parameters/max-wal-senders/) · [`max_replication_slots`](/parameters/max-replication-slots/) · [`debug_logical_replication_streaming`](/parameters/debug-logical-replication-streaming/) · [`temp_file_limit`](/parameters/temp-file-limit/)

## References {#references}

- [PostgreSQL 19 Beta 3 — logical_decoding_work_mem](https://www.postgresql.org/docs/19/runtime-config-resource.html#GUC-LOGICAL-DECODING-WORK-MEM)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)