pg_class — PostgreSQL system catalog

The PostgreSQL pg_class system catalog: full column reference (names, types, descriptions), catalog relationships and version support.

The Sev-1 Admin
The Sev-1 Admin  ·  6 min read

Summary

The catalog pg_class describes tables and other objects that have columns or are otherwise similar to a table. This includes indexes (but see also pg_index), sequences (but see also pg_sequence), views, materialized views, composite types, and TOAST tables; see relkind. Below, when we mean all of these kinds of objects we speak of “relations”. Not all of pg_class’s columns are meaningful for all relation kinds.

(Description quoted from the official PostgreSQL documentation.)

Columns

The pg_class system catalog exposes the following columns (names, types and descriptions are taken verbatim from the PostgreSQL documentation):

  • oid oid
    Row identifier
  • relname name
    Name of the table, index, view, etc.
  • relnamespace oid references pg_namespace.oid
    The OID of the namespace that contains this relation
  • reltype oid references pg_type.oid
    The OID of the data type that corresponds to this table’s row type, if any; zero for indexes, sequences, and TOAST tables, which have no pg_type entry
  • reloftype oid references pg_type.oid
    For typed tables, the OID of the underlying composite type; zero for all other relations
  • relowner oid references pg_authid.oid
    Owner of the relation
  • relam oid references pg_am.oid
    The access method used to access this table or index. Not meaningful if the relation is a sequence or has no on-disk file, except for partitioned tables, where, if set, it takes precedence over default_table_access_method when determining the access method to use for partitions created when one is not specified in the creation command.
  • relfilenode oid
    Name of the on-disk file of this relation; zero means this is a “mapped” relation whose disk file name is determined by low-level state
  • reltablespace oid references 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, except for partitioned tables, where this is the tablespace in which partitions will be created when one is not specified in the creation command.
  • 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 live 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. If the table has never yet been vacuumed or analyzed, reltuples contains -1 indicating that the row count is unknown.
  • relallvisible int4
    Number of pages that are marked all-visible in the table’s visibility map. This is only an estimate used by the planner. It is updated by VACUUM, ANALYZE, and a few DDL commands such as CREATE INDEX.
  • relallfrozen int4
    Number of pages that are marked all-frozen in the table’s visibility map. This is only an estimate used for triggering autovacuums. It can also be used along with relallvisible for scheduling manual vacuums and tuning vacuum’s freezing behavior. It is updated by VACUUM, ANALYZE, and a few DDL commands such as CREATE INDEX.
  • reltoastrelid oid references pg_class.oid
    OID of the TOAST table associated with this table, zero if none. The TOAST table stores large attributes “out of line” in a secondary table.
  • relhasindex bool
    True if this is a table and it has (or recently had) any 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.
  • relpersistence char
    p = permanent table/sequence, u = unlogged table/sequence, t = temporary table/sequence
  • relkind char
    r = ordinary table, i = index, S = sequence, t = TOAST table, v = view, m = materialized view, c = composite type, f = foreign table, p = partitioned table, I = partitioned index, g = property graph
  • 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
  • relhasrules bool
    True if table has (or once had) rules; see pg_rewrite catalog
  • relhastriggers bool
    True if table has (or once had) triggers; see pg_trigger catalog
  • relhassubclass bool
    True if table or index has (or once had) any inheritance children or partitions
  • relrowsecurity bool
    True if table has row-level security enabled; see pg_policy catalog
  • relforcerowsecurity bool
    True if row-level security (when enabled) will also apply to table owner; see pg_policy catalog
  • relispopulated bool
    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 (same as nothing if the index used has been dropped)
  • relispartition bool
    True if table or index is a partition
  • relrewrite oid references pg_class.oid
    For new relations being written during a DDL operation that requires a table rewrite, this contains the OID of the original relation; otherwise zero. That state is only visible internally; this field should never contain anything other than zero for a user-visible relation.
  • 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. Zero (InvalidTransactionId) if the relation is not a table.
  • 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; see ddl_priv for details
  • reloptions text[]
    Access-method-specific options, as “keyword=value” strings
  • relpartbound pg_node_tree
    If table is a partition (see relispartition), internal representation of the partition bound

Related catalogs

This object references the following other system catalogs:

Version applicability

Present in PostgreSQL 17, 18, 19 (verified against each release’s documentation). This is a long-standing system object that also exists in earlier PostgreSQL releases.

Related & references

Reference: PostgreSQL documentation — pg_class.