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
| Name | Type | References | Description |
|---|---|---|---|
| relname | name | Name of the table, index, view, etc. | |
| reltype | oid | pg_type.oid | The data type that corresponds to this table (not functional, only set for system tables) |
| 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 approximate value which is calculated during vacuum. | |
| reltuples | int4 | Number of tuples in the table. This is only an estimate used by the planner, updated by VACUUM. | |
| 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 | Oid of the index on the TOAST table for this table, 0 if none |
| relhasindex | bool | True if this is a table and it has at least one index | |
| relisshared | bool | XXX (This is not what it seems to be.) | |
| relkind | char | 'r' = ordinary table, 'i' = index, 'S' = sequence, 'v' = view, 's' = special, 't' = secondary TOAST table | |
| relnatts | int2 | Number of columns in the relation, besides system columns. 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 or something.) | |
| relfkeys | int2 | Number foreign keys on the table | |
| relhaspkey | bool | unused (No, this does not say whether the table has a primary key. It's really unused.) | |
| relhasrules | bool | Table has rules | |
| relhassubclass | bool | At least one table inherits this one | |
| relacl | aclitem[] | Access permissions. See the descriptions of GRANT and REVOKE for details. |