PostgreSQL: who is locking my table?

See http://stackoverflow.com/questions/17605511/why-would-alter-table-drop-constraint-on-an-empty-table-take-a-long-time

1 2 3 4 5 6 7 8

select   c.relname,   l.*,   psa.* from pg_locks l inner join pg_stat_activity psa ON (psa.pid = l.pid) left outer join pg_class c ON (l.relation = c.oid) where l.relation = 'prov_db.ht_request_status'::regclass;