A deep-dive guide for contributors working on PostgreSQL logical replication, written by Fujitsu engineers. Covers practical lessons across four contribution areas: performance optimization (profiling with perf, eliminating unnecessary relcache access), bug fixing (using BuildFarm and Patch Tester, analyzing feature intersections like MERGE command), code refactoring, and new features. Also addresses publication DDL semantics, lazy vs. eager validation, upgrade/downgrade compatibility across major versions, historic snapshot behavior in catalog lookups, subscriber worker architecture (apply, parallel apply, tablesync, sequencesync workers), and why physical replication patterns don't always translate to logical replication. Emphasizes streaming mode as the primary optimization target.
