Reading The Internals of PostgreSQL: Database Cluster, Databases, and Tables
Summary
A technical note detailing PostgreSQL internals, including the concepts of database clusters, per-database catalogs, OIDs, and the physical storage layout under PGDATA. It covers system catalogs (pg_class, pg_database), databases and tables, tablespaces, and the TOAST mechanism, with practical SQL examples and references to the PostgreSQL source and documentation.