How to find the id of a session which holds the lock on record

Question

Hi,
I need to find the session id of a user who holds a lock on the records that i need to update.
for example if a user 'A' is update a emp record where emp = 15 and is holding a lock on it. And now when user 'B' tries to get a lock on the same record either he has to wait indefinitely till 'A' releases the lock or he has to skip that record to get lock.
But how can user 'B' find that 'A' holds the lock on that record ?
Can any one please help me ?
Thanks in Advance
Kalyan

Answer 1

try this:
---session A---------
test > conn hr/hr
Connected.
test > update employees set salary=100 where First_name='Shelley';
1 row updated.
-----session B--------
test > conn hr/hr
Connected.
test > set serveroutput on
test > DECLARE
  2     CURSOR sal_cursor IS
  3     SELECT *
  4     FROM employees
  5     WHERE First_name='Shelley'
  6     FOR UPDATE OF salary NOWAIT;
  7
  8     e_emps_locked EXCEPTION;
  9     PRAGMA EXCEPTION_INIT
10     (e_emps_locked, -54);
11  BEGIN
12  FOR emp_record IN sal_cursor
13  LOOP
14     UPDATE employees
15     SET salary = emp_record.salary * 1.10
16     WHERE CURRENT OF sal_cursor;
17  END LOOP;
18  EXCEPTION
19     WHEN e_emps_locked then
20     DBMS_OUTPUT.PUT_LINE ('Cannot update employees ' ||
21     'Shelley' || ' was locked by others. ');
22  END;
23  /
Cannot update employees Shelley was locked by others.
PL/SQL procedure successfully completed.