Exploring versions of the Postgres logical replication protocol

Logical Replication is one of the many ways a Postgres database can replicate data to other Postgres database (a.k.a standby). Logical replication directly reads from the write-ahead log (WAL), recording every database change, avoiding the need to intercept queries or periodically read the table. These changes are filtered, serialized and then sent to the standby servers where they can be applied. While logical replication is intended to be used by Postgres databases to send and receive changes, it also allows ETL tools like PeerDB to get a reliable stream of changes that can be processed as needed.

Logical replication started by only allowing streaming of committed transactions. It then evolved to support in-flight transactions followed by two-phase commits and then parallel apply of in-flight transactions. This blog will dive into this evolution, its impact on performance, and present some useful benchmarks. This blog is useful for anyone who uses Postgres Logical Replication in practice!

For a quick rundown, a full logical replication setup involves several crucial components. Please skip this section if you are already familiar with the concepts of logical replication.

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