# 51.11 pg\_class

The catalog `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.

#### **Table 51.11. `pg_class` Columns**

| <p>Column Type</p><p>Description</p>                                                                                                                                                                                                                                                                                                                                                                                                                           |
| -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| <p><code>oid</code> <code>oid</code></p><p>Row identifier</p>                                                                                                                                                                                                                                                                                                                                                                                                  |
| <p><code>relname</code> <code>name</code></p><p>Name of the table, index, view, etc.</p>                                                                                                                                                                                                                                                                                                                                                                       |
| <p><code>relnamespace</code> <code>oid</code> (references <a href="https://www.postgresql.org/docs/13/catalog-pg-namespace.html"><code>pg\_namespace</code></a>.<code>oid</code>)</p><p>The OID of the namespace that contains this relation</p>                                                                                                                                                                                                               |
| <p><code>reltype</code> <code>oid</code> (references <a href="https://www.postgresql.org/docs/13/catalog-pg-type.html"><code>pg\_type</code></a>.<code>oid</code>)</p><p>The OID of the data type that corresponds to this table's row type, if any (zero for indexes, which have no <code>pg\_type</code> entry)</p>                                                                                                                                          |
| <p><code>reloftype</code> <code>oid</code> (references <a href="https://www.postgresql.org/docs/13/catalog-pg-type.html"><code>pg\_type</code></a>.<code>oid</code>)</p><p>For typed tables, the OID of the underlying composite type, zero for all other relations</p>                                                                                                                                                                                        |
| <p><code>relowner</code> <code>oid</code> (references <a href="https://www.postgresql.org/docs/13/catalog-pg-authid.html"><code>pg\_authid</code></a>.<code>oid</code>)</p><p>Owner of the relation</p>                                                                                                                                                                                                                                                        |
| <p><code>relam</code> <code>oid</code> (references <a href="https://www.postgresql.org/docs/13/catalog-pg-am.html"><code>pg\_am</code></a>.<code>oid</code>)</p><p>If this is a table or an index, the access method used (heap, B-tree, hash, etc.)</p>                                                                                                                                                                                                       |
| <p><code>relfilenode</code> <code>oid</code></p><p>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</p>                                                                                                                                                                                                                                                                 |
| <p><code>reltablespace</code> <code>oid</code> (references <a href="https://www.postgresql.org/docs/13/catalog-pg-tablespace.html"><code>pg\_tablespace</code></a>.<code>oid</code>)</p><p>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.)</p>                                                                                                   |
| <p><code>relpages</code> <code>int4</code></p><p>Size of the on-disk representation of this table in pages (of size <code>BLCKSZ</code>). This is only an estimate used by the planner. It is updated by <code>VACUUM</code>, <code>ANALYZE</code>, and a few DDL commands such as <code>CREATE INDEX</code>.</p>                                                                                                                                              |
| <p><code>reltuples</code> <code>float4</code></p><p>Number of live rows in the table. This is only an estimate used by the planner. It is updated by <code>VACUUM</code>, <code>ANALYZE</code>, and a few DDL commands such as <code>CREATE INDEX</code>.</p>                                                                                                                                                                                                  |
| <p><code>relallvisible</code> <code>int4</code></p><p>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 <code>VACUUM</code>, <code>ANALYZE</code>, and a few DDL commands such as <code>CREATE INDEX</code>.</p>                                                                                                                                                       |
| <p><code>reltoastrelid</code> <code>oid</code> (references <a href="https://www.postgresql.org/docs/13/catalog-pg-class.html"><code>pg\_class</code></a>.<code>oid</code>)</p><p>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.</p>                                                                                                                                 |
| <p><code>relhasindex</code> <code>bool</code></p><p>True if this is a table and it has (or recently had) any indexes</p>                                                                                                                                                                                                                                                                                                                                       |
| <p><code>relisshared</code> <code>bool</code></p><p>True if this table is shared across all databases in the cluster. Only certain system catalogs (such as <code>pg\_database</code>) are shared.</p>                                                                                                                                                                                                                                                         |
| <p><code>relpersistence</code> <code>char</code></p><p><code>p</code> = permanent table, <code>u</code> = unlogged table, <code>t</code> = temporary table</p>                                                                                                                                                                                                                                                                                                 |
| <p><code>relkind</code> <code>char</code></p><p><code>r</code> = ordinary table, <code>i</code> = index, <code>S</code> = sequence, <code>t</code> = TOAST table, <code>v</code> = view, <code>m</code> = materialized view, <code>c</code> = composite type, <code>f</code> = foreign table, <code>p</code> = partitioned table, <code>I</code> = partitioned index</p>                                                                                       |
| <p><code>relnatts</code> <code>int2</code></p><p>Number of user columns in the relation (system columns not counted). There must be this many corresponding entries in <code>pg\_attribute</code>. See also <code>pg\_attribute.attnum</code>.</p>                                                                                                                                                                                                             |
| <p><code>relchecks</code> <code>int2</code></p><p>Number of <code>CHECK</code> constraints on the table; see <a href="https://www.postgresql.org/docs/13/catalog-pg-constraint.html"><code>pg\_constraint</code></a> catalog</p>                                                                                                                                                                                                                               |
| <p><code>relhasrules</code> <code>bool</code></p><p>True if table has (or once had) rules; see <a href="https://www.postgresql.org/docs/13/catalog-pg-rewrite.html"><code>pg\_rewrite</code></a> catalog</p>                                                                                                                                                                                                                                                   |
| <p><code>relhastriggers</code> <code>bool</code></p><p>True if table has (or once had) triggers; see <a href="https://www.postgresql.org/docs/13/catalog-pg-trigger.html"><code>pg\_trigger</code></a> catalog</p>                                                                                                                                                                                                                                             |
| <p><code>relhassubclass</code> <code>bool</code></p><p>True if table or index has (or once had) any inheritance children</p>                                                                                                                                                                                                                                                                                                                                   |
| <p><code>relrowsecurity</code> <code>bool</code></p><p>True if table has row level security enabled; see <a href="https://www.postgresql.org/docs/13/catalog-pg-policy.html"><code>pg\_policy</code></a> catalog</p>                                                                                                                                                                                                                                           |
| <p><code>relforcerowsecurity</code> <code>bool</code></p><p>True if row level security (when enabled) will also apply to table owner; see <a href="https://www.postgresql.org/docs/13/catalog-pg-policy.html"><code>pg\_policy</code></a> catalog</p>                                                                                                                                                                                                          |
| <p><code>relispopulated</code> <code>bool</code></p><p>True if relation is populated (this is true for all relations other than some materialized views)</p>                                                                                                                                                                                                                                                                                                   |
| <p><code>relreplident</code> <code>char</code></p><p>Columns used to form “replica identity” for rows: <code>d</code> = default (primary key, if any), <code>n</code> = nothing, <code>f</code> = all columns, <code>i</code> = index with <code>indisreplident</code> set (same as nothing if the index used has been dropped)</p>                                                                                                                            |
| <p><code>relispartition</code> <code>bool</code></p><p>True if table or index is a partition</p>                                                                                                                                                                                                                                                                                                                                                               |
| <p><code>relrewrite</code> <code>oid</code> (references <a href="https://www.postgresql.org/docs/13/catalog-pg-class.html"><code>pg\_class</code></a>.<code>oid</code>)</p><p>For new relations being written during a DDL operation that requires a table rewrite, this contains the OID of the original relation; otherwise 0. That state is only visible internally; this field should never contain anything other than 0 for a user-visible relation.</p> |
| <p><code>relfrozenxid</code> <code>xid</code></p><p>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 <code>pg\_xact</code> to be shrunk. Zero (<code>InvalidTransactionId</code>) if the relation is not a table.</p>                                                   |
| <p><code>relminmxid</code> <code>xid</code></p><p>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 <code>pg\_multixact</code> to be shrunk. Zero (<code>InvalidMultiXactId</code>) if the relation is not a table.</p>                                                                             |
| <p><code>relacl</code> <code>aclitem\[]</code></p><p>Access privileges; see <a href="https://www.postgresql.org/docs/13/ddl-priv.html">Section 5.7</a> for details</p>                                                                                                                                                                                                                                                                                         |
| <p><code>reloptions</code> <code>text\[]</code></p><p>Access-method-specific options, as “keyword=value” strings</p>                                                                                                                                                                                                                                                                                                                                           |
| <p><code>relpartbound</code> <code>pg\_node\_tree</code></p><p>If table is a partition (see <code>relispartition</code>), internal representation of the partition bound</p>                                                                                                                                                                                                                                                                                   |

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, `VACUUM` clears `relhasindex` if it finds the table has no indexes. This arrangement avoids race conditions and improves concurrency.<br>


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