Hands-on Lab·PostgreSQL

PostgreSQL Logical Replication

Replicate one table into a writable database on another cluster. Then add a column on the publisher and watch the apply worker die while the subscription still reports itself enabled.

Replication Guide 32 of 47 Advanced

OSUbuntu 26.04 LTS (resolute)
PostgreSQL18.6-0ubuntu0.26.04.1
Hostsdb-a01 / db-b01 / db-c01, 2 core / 4 GB each
TimeAbout 21 min
Reviewed27 August 2026

Written against the versions above. PostgreSQL 18 validates the subscription's target relations when you run `CREATE SUBSCRIPTION`, so a missing table is refused immediately. On earlier versions the subscription is created and the worker fails afterwards.

The 3 hosts these commands ran on: db-a01, db-b01, db-c01.
Server Name	IP Address	OS	Roles	CPU	RAM	HDD
db-a01	192.168.0.81	Ubuntu 26.04 LTS	Primary / Source / Replica Set Member 1	2 Core	4 GB	50 GB
db-b01	192.168.0.82	Ubuntu 26.04 LTS	Standby / Replica / Replica Set Member 2	2 Core	4 GB	50 GB
db-c01	192.168.0.83	Ubuntu 26.04 LTS	Replica Set Member 3 / Cascading and Delayed Replica	2 Core	4 GB	50 GB

Before you start

Two clusters, and a restart window on the publisher - wal_level needs one.
The replicator role with the REPLICATION attribute.

Logical decoding needs more in the WAL than replication does
Publish a subset
The subscriber connects to a database, not to `replication`
The schema is not replicated either
Watch changes flow
The subscriber is writable, and that is the trap
Add a column, and break it
Tear it down properly

Official sources

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PostgreSQL Logical Replication

Before you start

Logical decoding needs more in the WAL than replication does

Publish a subset

The subscriber connects to a database, not to `replication`

The schema is not replicated either

Watch changes flow

The subscriber is writable, and that is the trap

Add a column, and break it

Tear it down properly

Official sources