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

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;