Four Hidden Pitfalls of PostgreSQL Logical Replication for Reporting Replicas

PostgreSQL logical replication allows selective table syncing, extra indexes on replicas, and cross-version setups, making it attractive for reporting workloads over physical replication. However, a key operational hazard is that schema changes such as ALTER TABLE or CREATE INDEX are never replicated, meaning DDL must be manually applied to the subscriber in sync with the publisher. Replication slots pose another serious risk: if a subscriber disconnects without dropping its slot, the publisher retains all WAL segments indefinitely, which can silently fill disk and crash the primary database. These failure modes are often delayed and invisible, making them especially dangerous in production environments. The article argues that logical replication's flexibility over physical fidelity comes with a hidden operational cost that official documentation tends to understate.