# debug_logical_replication_streaming

> debug_logical_replication_streaming — Forces immediate streaming or serialization of changes in large transactions. Observed in PG16–19 Beta 3; its last measured boot default is buffered 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:** “Forces immediate streaming or serialization of changes in large transactions.”

## 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 | `buffered`, `immediate` | — for non-enum types |
| Category | Developer Options | Upstream classification |
| Latest boot value | `buffered` | buffered |
{.fields meta="-"}

## Lifecycle {#lifecycle}

| Fact | Value |
| --- | --- |
| First observed | PG16 |
| Present in | PG16–19 Beta 3 |
| Removed in | No |
| Introduction commit | [`39d4207e876f`](https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=39d4207e876fa55971cd20a7677b78f067971fd3) — Rename logical_replication_mode to debug_logical_replication_streaming |
| Commit date | 2023-08-29 |
| Discussion | [thread 1](https://www.postgresql.org/message-id/flat/d672d774-c44b-6fec-f993-793e744f169a%40eisentraut.org) |

## Default history {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG16–19 Beta 3 | `buffered` | — | buffered |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

debug_logical_replication_streaming forces large-transaction logical replication paths to stream or serialize immediately instead of waiting for normal buffering thresholds. buffered is the production behavior.

On a publisher, immediate streams each change when subscription streaming is enabled or serializes it otherwise, bypassing the logical_decoding_work_mem trigger. On a parallel subscriber, immediate forces file serialization instead of the normal shared-memory queue path.

The two sides therefore exercise different code paths. This is a regression and fault-reproduction control, not a latency or memory tuning shortcut. 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 | Do not tune production OLTP with debug_logical_replication_streaming. Enable it only for a bounded reproduction with an owner, log/disk budget, rollback condition, and evidence-capture plan; restore the default immediately afterward. |
| OLAP | Long analytical runs can amplify debug_logical_replication_streaming's debug overhead and artifacts. Prefer standard EXPLAIN and statistics first, and isolate any developer experiment from normal users. |
| Small nodes | Keep debug_logical_replication_streaming at its upstream default. A small host has less spare CPU, disk, connection, and log capacity for developer instrumentation. |
{.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: PG16–19 Beta 3 unmodified; OLAP: PG16–19 Beta 3 unmodified; CRIT: PG16–19 Beta 3 unmodified; TINY: PG16–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

## Common pitfalls {#common-pitfalls}

- Leaving debug_logical_replication_streaming enabled after the bounded diagnostic or recovery task.
- Running the experiment on the only copy of production data.
- Underestimating log, core-file, temporary-file, WAL, CPU, or connection-slot amplification.
- Treating a server that merely starts or completes a query as proof that data and behavior are correct.

## Related parameters {#related-parameters}

[`logical_decoding_work_mem`](/parameters/logical-decoding-work-mem/) · [`max_logical_replication_workers`](/parameters/max-logical-replication-workers/) · [`max_sync_workers_per_subscription`](/parameters/max-sync-workers-per-subscription/) · [`wal_level`](/parameters/wal-level/)

## References {#references}

- [PostgreSQL 19 Beta 3 — debug_logical_replication_streaming](https://www.postgresql.org/docs/19/runtime-config-developer.html#GUC-DEBUG-LOGICAL-REPLICATION-STREAMING)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)