Script to find locks in the database

select
 (select username || ' - ' || osuser from v$session where sid=a.sid) blocker,
 a.sid || ', ' ||
 (select serial# from v$session where sid=a.sid) sid_serial,
 ' is blocking ',
 (select username || ' - ' || osuser from v$session where sid=b.sid) blockee,
 b.sid || ', ' ||
 (select serial# from v$session where sid=b.sid) sid_serial
 from v$lock a, v$lock b
 where a.block = 1
   and b.request > 0
   and a.id1 = b.id1
   and a.id2 = b.id2;