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. |