pgclass

pg_class is a system catalog relation in PostgreSQL that stores metadata for every relation in a database. It resides in the pg_catalog schema and is one of the core catalogs used to describe database objects. Each row represents a relation, which can be a regular table, index, sequence, view, materialized view, partitioned table, foreign table, or a TOAST-related object. The object identifier (oid) uniquely identifies the row; other fields provide the object's name (relname), its namespace (relnamespace), and its owner (relowner). The relkind column encodes the kind of relation, with common codes such as r for ordinary tables, i for indexes, S for sequences, v for views, m for materialized views, f for foreign tables, t for TOAST tables, and p for partitioned tables.

Other important fields capture storage and statistics. reltablespace indicates the tablespace for the relation’s files, relpages shows the on-disk page count, and reltuples provides an estimate of the number of rows. relnatts records the number of attributes (columns) in the relation. There are boolean flags such as relhasindex, relhasrules, relhastriggers, and relrowsecurity that indicate whether related features exist for the relation. The reltoastrelid column links to the related TOAST table used for large attributes, and relacl stores access privileges. The relfilenode field identifies the underlying physical file on disk for the relation.

Usage and interpretation: pg_class is queried to inspect catalog metadata and is often joined with pg_namespace to obtain schema-qualified names or with pg_roles to display owners. It is essential for understanding object types, sizes, and basic statistics used by the planner and administrator tools. Direct modification of pg_class is discouraged; changes are made via DDL commands and internal server operations.