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

Type , Valueenum: Upstream pg_settings type
Context , Valueuser: Settable by an ordinary user
Unit , Value—: Raw unit
Range , Value—: Raw limits in the last observed version
Enum values , Valuebuffered, immediate: — for non-enum types
Category , ValueDeveloper Options: Upstream classification
Latest boot value , Valuebuffered: buffered

Lifecycle

Fact	Value
First observed	PG16
Present in	PG16–19 Beta 3
Removed in	No
Introduction commit	`39d4207e876f` — Rename logical_replication_mode to debug_logical_replication_streaming
Commit date	2023-08-29
Discussion	thread 1

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG16–19 Beta 3	`buffered`	—	buffered

How it works

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

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.

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	—	—

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

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.

logical_decoding_work_mem · max_logical_replication_workers · max_sync_workers_per_subscription · wal_level