pg_index
The catalog pg_index contains part of the information about indexes. The rest is mostly in pg_class.
Table pg_index Columns
| Column Type Description | 
|---|
 The OID of the pg_class entry for this index  | 
 The OID of the pg_class entry for the table this index is for  | 
 The total number of columns in the index (duplicates   | 
 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  | 
 If true, this is a unique index  | 
 If true, this index represents the primary key of the table (  | 
 If true, this index supports an exclusion constraint  | 
 If true, the uniqueness check is enforced immediately on insertion (irrelevant if   | 
 If true, the table was last clustered on this index  | 
 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.  | 
 If true, queries must not use the index until the   | 
 If true, the index is currently ready for inserts. False means the index must be ignored by INSERT/UPDATE operations.  | 
 If false, the index is in process of being dropped, and should be ignored for all purposes (including HOT-safety decisions)  | 
 If true this index has been chosen as “replica identity” using ALTER TABLE ... REPLICA IDENTITY USING INDEX ...  | 
 This is an array of   | 
 For each column in the index key (  | 
 For each column in the index key (  | 
 This is an array of   | 
 Expression trees (in   | 
 Expression tree (in   |