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)
reloftype oid pg_type.oid The OID of an entry in pg_type for an underlying composite type.
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.
relallvisible int32   Number of all-visible blocks (this value may not be up-to-date).
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.
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.
relpersistence char   The type of object persistence: p = heap or append-optimized table, u = unlogged temporary table, t = temporary table.
relkind char   The type of object

r = heap or append-optimized table, i = index, S = sequence, t = TOAST value, v = view, c = composite type, f = foreign table, u = uncatalogued temporary heap table, o = internal append-optimized segment files and EOFs, b = append-only block directory, M = append-only visibility map
relstorage char   The storage mode of a table

a= 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.
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.
relhastriggers boolean   True if table has (or once had) triggers.
relhassubclass boolean   True if table has (or once had) any inheritance children.
relispopulated boolean   True if relation is populated (this is true for all relations other than some materialized views).
relreplident char   Columns used to form “replica identity” for rows: d = default (primary key, if any), n = nothing, f = all columns i = index with indisreplident set, or default
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_xact 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.
relminmxid xid   All multixact IDs before this one have been replaced by a transaction ID in this table. This is used to track whether the table needs to be vacuumed in order to prevent multixact ID wraparound or to allow pg_multixact to be shrunk. Zero (InvalidMultiXactId) if the relation is not a table.
relacl aclitem[]   Access privileges assigned by GRANT and REVOKE.
reloptions text[]   Access-method-specific options, as “keyword=value” strings.

Parent topic: System Catalogs Definitions