51.26. `pg_index`
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## 51.26. `pg_index`

The catalog `pg_index` contains part of the information about indexes. The rest is mostly in `pg_class`.

Table 51.26. `pg_index` Columns

Name | Type | References | Description
--- | --- | --- | ---
`indexrelid` | `oid` | ``pg_class`.oid` | The OID of the `pg_class` entry for this index
`indrelid` | `oid` | ``pg_class`.oid` | The OID of the `pg_class` entry for the table this index is for
`indnatts` | `int2` |  | The total number of columns in the index (duplicates `pg_class.relnatts`); this number includes both key and included attributes
`indnkeyatts` | `int2` |  | The number of key columns in the index, not counting any included columns, which are merely stored and do not participate in the index semantics
`indisunique` | `bool` |  | If true, this is a unique index
`indisprimary` | `bool` |  | If true, this index represents the primary key of the table (`indisunique` should always be true when this is true)
`indisexclusion` | `bool` |  | If true, this index supports an exclusion constraint
`indimmediate` | `bool` |  | If true, the uniqueness check is enforced immediately on insertion (irrelevant if `indisunique` is not true)
`indisclustered` | `bool` |  | If true, the table was last clustered on this index
`indisvalid` | `bool` |  | If true, the index is currently valid for queries. False means the index is possibly incomplete: it must still be modified by `INSERT`/`UPDATE` operations, but it cannot safely be used for queries. If it is unique, the uniqueness property is not guaranteed true either.
`indcheckxmin` | `bool` |  | If true, queries must not use the index until the `xmin` of this `pg_index` row is below their `TransactionXmin` event horizon, because the table may contain broken HOT chains with incompatible rows that they can see
`indisready` | `bool` |  | If true, the index is currently ready for inserts. False means the index must be ignored by `INSERT`/`UPDATE` operations.
`indislive` | `bool` |  | If false, the index is in process of being dropped, and should be ignored for all purposes (including HOT-safety decisions)
`indisreplident` | `bool` |  | If true this index has been chosen as “replica identity” using `ALTER TABLE ... REPLICA IDENTITY USING INDEX ...`
`indkey` | `int2vector` | ``pg_attribute`.attnum` | This is an array of `indnatts` values that indicate which table columns this index indexes. For example a value of `1 3` would mean that the first and the third table columns make up the index entries. Key columns come before non-key (included) columns. A zero in this array indicates that the corresponding index attribute is an expression over the table columns, rather than a simple column reference.
`indcollation` | `oidvector` | ``pg_collation`.oid` | For each column in the index key (`indnkeyatts` values), this contains the OID of the collation to use for the index, or zero if the column is not of a collatable data type.
`indclass` | `oidvector` | ``pg_opclass`.oid` | For each column in the index key (`indnkeyatts` values), this contains the OID of the operator class to use. See `pg_opclass` for details.
`indoption` | `int2vector` |  | This is an array of `indnkeyatts` values that store per-column flag bits. The meaning of the bits is defined by the index's access method.
`indexprs` | `pg_node_tree` |  | Expression trees (in `nodeToString()` representation) for index attributes that are not simple column references. This is a list with one element for each zero entry in `indkey`. Null if all index attributes are simple references.
`indpred` | `pg_node_tree` |  | Expression tree (in `nodeToString()` representation) for partial index predicate. Null if not a partial index.

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