3.5. pg_class

pg_class catalogues tables and mostly everything else that has columns or is otherwise similar to a table. This includes indexes (but see pg_index), sequences, views, and some kinds of special relation kinds. 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

NameTypeReferencesDescription
relnamename Name of the table, index, view, etc.
reltypeoidpg_type.oid The data type that corresponds to this table (not functional, only set for system tables)
relownerint4pg_shadow.usesysidOwner of the relation
relamoidpg_am.oidIf this is an index, the access method used (btree, 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.oidOid of the index on the TOAST table for this table, 0 if none
relhasindexbool True if this is a table and it has at least one index
relissharedbool XXX (This is not what it seems to be.)
relkindchar  'r' = ordinary table, 'i' = index, 'S' = sequence, 'v' = view, 's' = special, 't' = secondary TOAST table
relnattsint2  Number of columns in the relation, besides system columns. 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 or something.)
relfkeysint2 Number foreign keys on the table
relhaspkeybool  unused (No, this does not say whether the table has a primary key. It's really unused.)
relhasrulesbool Table has rules
relhassubclassbool At least one table inherits this one
relaclaclitem[]  Access permissions. See the descriptions of GRANT and REVOKE for details.