pg_index

The pg_index system catalog table contains part of the information about indexes. The rest is mostly in pg_class_internal.

Table 1. pg_catalog.pg_index

column	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	smallint		The number of columns in the index (duplicates pg_class.relnatts)
indnkeyatts	smallint		The number of key columns in the index
indisunique	boolean		If true, this is a unique index
indisprimary	boolean		If true, this index represents the primary key of the table. (indisunique should always be true when this is true.)
indisexclusion	boolean		If true, this index supports an exclusion constraint
indimmediate	boolean		If true, the uniqueness check is enforced immediately on insertion (irrelevant if indisunique is not true)
indisclustered	boolean		If true, the table was last clustered on this index via the CLUSTERs command
indisvalid	boolean		If true, the index is currently valid for queries. False means the index is possibly incomplete: it must still be modified by INSERT/UPDATEs operations, but it cannot safely be used for queries.
indcheckxmin	boolean		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	boolean		If true, the index is currently ready for inserts. False means the index must be ignored by INSERT/UPDATE operations
indislive	boolean		If false, the index is in process of being dropped, and should be ignored for all purposes
indisreplident	boolean		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 key. 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		For each column in the index key, this contains the OID of the collation to use for the index.
indclass	oidvector	pg_opclass.oid	For each column in the index key this contains the OID of the operator class to use
indoption	int2vector		This is an array of indnatts 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.