43.12. pg_class

The catalog pg_class catalogs tables and most everything else that has columns or is otherwise similar to a table. This includes indexes (but see also pg_index), sequences, views, composite types, and TOAST tables; see relkind. Below, when we mean all of these kinds of objects we speak of "relations". Not all columns are meaningful for all relation types.

Table 43-12. pg_class Columns

relnamename Name of the table, index, view, etc.
relnamespaceoidpg_namespace.oid The OID of the namespace that contains this relation
reltypeoidpg_type.oid The OID of the data type that corresponds to this table's row type, if any (zero for indexes, which have no pg_type entry)
relowneroidpg_authid.oidOwner of the relation
relamoidpg_am.oidIf this is an index, the access method used (B-tree, hash, etc.)
relfilenodeoid Name of the on-disk file of this relation; 0 if none
reltablespaceoidpg_tablespace.oid The tablespace in which this relation is stored. If zero, the database's default tablespace is implied. (Not meaningful if the relation has no on-disk file.)
relpagesint4  Size of the on-disk representation of this table in pages (of size BLCKSZ). This is only an estimate used by the planner. It is updated by VACUUM, ANALYZE, and a few DDL commands such as CREATE INDEX
reltuplesfloat4  Number of rows in the table. This is only an estimate used by the planner. It is updated by VACUUM, ANALYZE, and a few DDL commands such as CREATE INDEX
reltoastrelidoidpg_class.oid OID of the TOAST table associated with this table, 0 if none. The TOAST table stores large attributes "out of line" in a secondary table
reltoastidxidoidpg_class.oid For a TOAST table, the OID of its index. 0 if not a TOAST table
relhasindexbool  True if this is a table and it has (or recently had) any indexes. This is set by CREATE INDEX, but not cleared immediately by DROP INDEX. VACUUM clears relhasindex if it finds the table has no indexes
relissharedbool  True if this table is shared across all databases in the cluster. Only certain system catalogs (such as pg_database) are shared
relkindchar  r = ordinary table, i = index, S = sequence, v = view, c = composite type, t = TOAST table
relnattsint2  Number of user columns in the relation (system columns not counted). There must be this many corresponding entries in pg_attribute. See also pg_attribute.attnum
relchecksint2  Number of check constraints on the table; see pg_constraint catalog
reltriggersint2  Number of triggers on the table; see pg_trigger catalog
relukeysint2 Unused (not the number of unique keys)
relfkeysint2 Unused (not the number of foreign keys on the table)
relrefsint2 Unused
relhasoidsbool  True if we generate an OID for each row of the relation
relhaspkeybool  True if the table has (or once had) a primary key
relhasrulesbool  True if table has rules; see pg_rewrite catalog
relhassubclassbool True if table has (or once had) any inheritance children
relfrozenxidxid  All transaction IDs before this one have been replaced with a permanent ("frozen") transaction ID in this table. This is used to track whether the table needs to be vacuumed in order to prevent transaction ID wraparound or to allow pg_clog to be shrunk. Zero (InvalidTransactionId) if the relation is not a table
relaclaclitem[]  Access privileges; see GRANT and REVOKE for details
reloptionstext[]  Access-method-specific options, as "keyword=value" strings