The catalog pg_class catalogs tables and most everything else that has columns or is otherwise similar to a table. This includes indexes (but see also pg_index), sequences, views, composite types, and TOAST tables; see relkind. Below, when we mean all of these kinds of objects we speak of "relations". Not all columns are meaningful for all relation types.
Table 44-12. pg_class Columns
| Name | Type | References | Description |
|---|---|---|---|
| relname | name | Name of the table, index, view, etc. | |
| relnamespace | oid | pg_namespace.oid | The OID of the namespace 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, 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 size BLCKSZ). This is only an estimate used by the planner. It is updated by VACUUM, ANALYZE, and a few DDL commands such as CREATE INDEX | |
| 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 such as 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, c = composite type, t = 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_constraint 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 | True if table has rules; see pg_rewrite catalog | |
| relhassubclass | bool | 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. Zero (InvalidTransactionId) if the relation is not a table | |
| relacl | aclitem[] | Access privileges; see GRANT and REVOKE for details | |
| reloptions | text[] | Access-method-specific options, as "keyword=value" strings |