How to find locks in postgres ?

Table pg_locks is very usefull...

select
 pg_stat_activity.datname,
 pg_class.relname,
 pg_locks.transaction,
 pg_locks.mode,
 pg_locks.granted,
 pg_stat_activity.usename,
 substr(pg_stat_activity.current_query,1,30),
 pg_stat_activity.query_start,
 age(now(),pg_stat_activity.query_start) as "age",
 pg_stat_activity.procpid
from 
 pg_stat_activity,
 pg_locks left outer join pg_class on (pg_locks.relation = pg_class.oid)  
 where
 pg_locks.pid=pg_stat_activity.procpid order by query_start;