48.11. pg_class
The catalogpg_class catalogs tables and most everything else that has columns or is otherwise similar to a table. This includes indexes (but see alsopg_index), sequences, views, materialized views, composite types, and TOAST tables; seerelkind. Below, when we mean all of these kinds of objects we speak of“relations”. Not all columns are meaningful for all relation types.
Table 48.11. pg_class Columns
| Name | Type | References | Description |
|---|---|---|---|
oid | oid | Row identifier (hidden attribute; must be explicitly selected) | |
relname | name | Name of the table, index, view, etc. | |
relnamespace | oid | | The OID of the namespace that contains this relation |
reltype | oid | | The OID of the data type that corresponds to this table's row type, if any (zero for indexes, which have nopg_type entry) |
reloftype | oid | | For typed tables, the OID of the underlying composite type, zero for all other relations |
relowner | oid | | Owner of the relation |
relam | oid | | If this is an index, the access method used (B-tree, hash, etc.) |
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 | | 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 sizeBLCKSZ). This is only an estimate used by the planner. It is updated byVACUUM,ANALYZE, and a few DDL commands such asCREATE INDEX. | |
reltuples | float4 | Number of rows in the table. This is only an estimate used by the planner. It is updated byVACUUM,ANALYZE, and a few DDL commands such asCREATE INDEX. | |
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 byVACUUM,ANALYZE, and a few DDL commands such asCREATE INDEX. | |
reltoastrelid | 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 | 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 aspg_database) are shared. | |
relpersistence | char | p = permanent table,u = unlogged table,t = temporary table | |
relkind | char | r = ordinary table,i = index,S = sequence,v = view,m = materialized view,c = composite type,t = TOAST table,f = foreign table | |
relnatts | int2 | Number of user columns in the relation (system columns not counted). There must be this many corresponding entries inpg_attribute. See alsopg_attribute.attnum. | |
relchecks | int2 | Number ofCHECK constraints on the table; seepg_constraint catalog | |
relhasoids | bool | True if we generate an OID for each row of the relation | |
relhaspkey | bool | True if the table has (or once had) a primary key | |
relhasrules | bool | True if table has (or once had) rules; seepg_rewrite catalog | |
relhastriggers | bool | True if table has (or once had) triggers; seepg_trigger catalog | |
relhassubclass | bool | True if table has (or once had) any inheritance children | |
relrowsecurity | bool | True if table has row level security enabled; seepg_policy catalog | |
relforcerowsecurity | bool | True if row level security (when enabled) will also apply to table owner; seepg_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 withindisreplident set (same as nothing if the index used has been dropped) | |
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 allowpg_clog 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 allowpg_multixact to be shrunk. Zero (InvalidMultiXactId) if the relation is not a table. | |
relacl | aclitem[] | Access privileges; seeGRANT andREVOKE for details | |
reloptions | text[] | Access-method-specific options, as“keyword=value” strings |
Several of the Boolean flags inpg_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 byCREATE INDEX, but it is never cleared byDROP INDEX. Instead,VACUUM clearsrelhasindex if it finds the table has no indexes. This arrangement avoids race conditions and improves concurrency.