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.

column type references description
relname name Name of the table, index, view, etc.
relnamespace oid pg_namespace.oid The OID of the namespace (schema) that contains this relation
reltype oid pg_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)
relowner oid pg_authid.oid Owner of the relation
relam oid pg_am.oid If this is an index, the access method used (B-tree, Bitmap, hash, etc.)
relfilenode oid Name of the on-disk file of this relation; 0 if none.
reltablespace oid pg_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.)
relpages int4 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.
reltuples float4 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.
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.
relaosegidxid oid Deprecated in Greenplum Database 3.4.
relaosegrelid oid Deprecatedin Greenplum Database 3.4.
relhasindex boolean 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.
relisshared boolean True if this table is shared across all databases in the system. Only certain system catalog tables are shared.
relkind char 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
relstorage char The storage mode of a tablea= append-optimized, c= column-oriented, h = heap, v = virtual, x= external table.
relnatts int2 Number of user columns in the relation (system columns not counted). There must be this many corresponding entries in pg_attribute.
relchecks int2 Number of check constraints on the table.
reltriggers int2 Number of triggers on the table.
relukeys int2 Unused
relfkeys int2 Unused
relrefs int2 Unused
relhasoids boolean True if an OID is generated for each row of the relation.
relhaspkey boolean True if the table has (or once had) a primary key.
relhasrules boolean True if table has rules.
relhassubclass boolean True if table has (or once had) any inheritance children.
relfrozenxid xid 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.
relacl aclitem[] Access privileges assigned by GRANT and REVOKE.
reloptions text[] Access-method-specific options, as "keyword=value" strings.

Parent topic: System Catalogs Definitions

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