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3.5. pg_class

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

Table 3-5. pg_class Columns

relnamename Name of the table, index, view, etc.
reltypeoidpg_type.oid The OID of the data type that corresponds to this table, if any (zero for indexes, which have no pg_type entry)
relownerint4pg_shadow.usesysidOwner 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
relpagesint4  Size of the on-disk representation of this table in pages (size BLCKSZ). This is only an estimate used by the planner. It is updated by VACUUM, ANALYZE, and CREATE INDEX.
reltuplesfloat4  Number of tuples in the table. This is only an estimate used by the planner. It is updated by VACUUM, ANALYZE, and 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, 's' = special, 't' = secondary 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_relcheck 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 Table has rules; see pg_rewrite catalog
relhassubclassbool At least one table inherits from this one
relaclaclitem[]  Access permissions. See the descriptions of GRANT and REVOKE for details.