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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 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.