Less important now, but they're unsafe to use prior to PG 10. As of 14.1, they still don't support unique constraints: select amname, pg_indexam_has_proper

Less important now, but they're unsafe to use prior to PG 10. As of 14.1, they still don't support unique constraints: select amname, pg_indexam_has_property(oid, 'can_unique') from pg_am amname | pg_indexam_has_property --------+------------------------- heap | ¤ btree | t hash | f gist | f gin | f spgist | f brin | f