pg_class catalogs tables and most everything else that has columns or is 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 columns are meaningful for all relation types.
Name of the table, index, view, etc.
The OID of the namespace that contains this relation
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
For typed tables, the OID of the underlying composite type; zero for all other relations
Owner of the relation
If this is a table or an index, the access method used (heap, B-tree, hash, etc.); otherwise zero (zero occurs for sequences, as well as relations without storage, such as views)
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
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.)
Size of the on-disk representation of this table in pages (of size
Number of live rows in the table. This is only an estimate used by the planner. It is updated by
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.
True if this is a table and it has (or recently had) any indexes
True if this table is shared across all databases in the cluster. Only certain system catalogs (such as
Number of user columns in the relation (system columns not counted). There must be this many corresponding entries in
True if table has (or once had) rules; see
True if table has (or once had) triggers; see
True if table or index has (or once had) any inheritance children or partitions
True if table has row-level security enabled; see
True if row-level security (when enabled) will also apply to table owner; see
True if relation is populated (this is true for all relations other than some materialized views)
Columns used to form “replica identity” for rows:
True if table or index is a partition
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.
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
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
Access privileges; see Section 5.7 for details
Access-method-specific options, as “keyword=value” strings
If table is a partition (see
Several of the Boolean flags in
pg_class are maintained lazily: they are guaranteed to be true if that's the correct state, but may not be reset to false immediately when the condition is no longer true. For example,
relhasindex is set by
CREATE INDEX, but it is never cleared by
DROP INDEX. Instead,
relhasindex if it finds the table has no indexes. This arrangement avoids race conditions and improves concurrency.