pg_class

The system catalog table pg_class catalogs tables and most everything else that has columns or is otherwise similar to a table (also known as relations). This includes indexes (see also pg_index), sequences, views, composite types, and TOAST tables. Not all columns are meaningful for all relation types.

columntypereferencesdescription
relnamename Name of the table, index, view, etc.
relnamespaceoidpg_namespace.oidThe OID of the namespace (schema) that contains this relation
reltypeoidpg_type.oidThe 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, Bitmap, hash, etc.)
relfilenodeoid Name of the on-disk file of this relation; 0 if none.
reltablespaceoidpg_tablespace.oidThe 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 32K each). This is only an estimate used by the planner. It is updated by VACUUM, ANALYZE, and a few DDL commands.
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.
reltoastrelidoidpg_class.oidOID 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.oidFor a TOAST table, the OID of its index. 0 if not a TOAST table.
relaosegidxidoid Deprecated in Greenplum Database 3.4.
relaosegrelidoid Deprecatedin Greenplum Database 3.4.
relhasindexboolean 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 will clear if it finds the table has no indexes.
relissharedboolean True if this table is shared across all databases in the system. Only certain system catalog tables are shared.
relkindchar The type of object
i = index, r = heap or append-optimized table, S = sequence, u = uncataloged temporary heap table, t = TOAST value, o = internal append-optimized segment files and EOFs, b = append-optimized block directory, m = append-only visibility map, v = view, c = composite type
relstoragechar The storage mode of a tablea= append-optimized, c= column-oriented, h = heap, v = virtual, x= external table.
relnattsint2 Number of user columns in the relation (system columns not counted). There must be this many corresponding entries in pg_attribute.
relchecksint2 Number of check constraints on the table.
reltriggersint2 Number of triggers on the table.
relukeysint2 Unused
relfkeysint2 Unused
relrefsint2 Unused
relhasoidsboolean True if an OID is generated for each row of the relation.
relhaspkeyboolean True if the table has (or once had) a primary key.
relhasrulesboolean True if table has rules.
relhassubclassboolean 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.
The value is 0 (InvalidTransactionId) if the relation is not a table or if the table does not require vacuuming to prevent transaction ID wraparound. The table still might require vacuuming to reclaim disk space.
relaclaclitem[] Access privileges assigned by GRANT and REVOKE.
reloptionstext[] Access-method-specific options, as “keyword=value” strings.

Parent topic: System Catalogs Definitions