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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 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

Name Type References Description
relname name   Name of the table, index, view, etc.
reltype oid pg_type.oid The OID of the data type that corresponds to this table, if any (zero for indexes, which have no pg_type entry)
relowner int4 pg_shadow.usesysid Owner of the relation
relam oid pg_am.oid If this is an index, the access method used (btree, hash, etc.)
relfilenode oid   Name of the on-disk file of this relation
relpages int4   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.
reltuples float4   Number of tuples in the table. This is only an estimate used by the planner. It is updated by VACUUM, ANALYZE, and CREATE INDEX.
reltoastrelid oid pg_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.
reltoastidxid oid pg_class.oid For a TOAST table, the OID of its index. 0 if not a TOAST table.
relhasindex bool   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.
relisshared bool   True if this table is shared across all databases in the cluster. Only certain system catalogs (such as pg_database) are shared.
relkind char   'r' = ordinary table, 'i' = index, 'S' = sequence, 'v' = view, 's' = special, 't' = secondary TOAST table
relnatts int2   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.
relchecks int2   Number of check constraints on the table; see pg_relcheck catalog
reltriggers int2   Number of triggers on the table; see pg_trigger catalog
relukeys int2   unused (Not the number of unique keys)
relfkeys int2   unused (Not the number of foreign keys on the table)
relrefs int2   unused
relhasoids bool   True if we generate an OID for each row of the relation.
relhaspkey bool   True if the table has (or once had) a primary key.
relhasrules bool   Table has rules; see pg_rewrite catalog
relhassubclass bool   At least one table inherits from this one
relacl aclitem[]   Access permissions. See the descriptions of GRANT and REVOKE for details.