What really happens to a single INSERT in PostgreSQL once it enters the system? In this talk, we trace the complete lifecycle of one tuple as it travels through PostgreSQL’s logical replication pipeline. Starting at the executor, we watch the tuple become a WAL record, explore what changes when wal_level=logical, and reveal how the logical decoding layer reconstructs row-level changes from low-level WAL fragments. We’ll step through the inner workings of the ReorderBuffer, explain how replication slots guarantee durability, and show how output plugins convert decoded changes into a logical stream ready for subscribers.
On the receiving side, we follow the apply worker as it processes transactions, resolves ordering, handles conflicts, and replays the change into the subscriber database. By the end, you’ll have a clear mental model of each stage—from WAL generation to apply—and a deeper understanding of how PostgreSQL reliably moves data through logical replication.
Whether you run logical replication, build CDC pipelines, or simply want to understand the internals behind one of PostgreSQL’s most powerful features, this talk will give you a guided, intuitive, and highly practical look behind the scenes.
