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.

Table 1. pg_catalog.pg_class
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_clog` 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.