Can you explain what pg_catalog is in PostgreSQL and what role it plays?

pg_catalog is a system schema in PostgreSQL that contains system tables and views with database metadata. It stores information about tables, indexes, data types, functions, access rights, and other database objects.

For example, the pg_catalog.pg_tables table contains information about all tables in the database, and pg_catalog.pg_class about object classes (tables, indexes, etc.).

This schema is used internally by PostgreSQL and is accessible to users for obtaining information about the database structure and status. It is usually referenced when writing queries that analyze metadata or during debugging.