We recently had a locking/blocking problem on two different 10.2.0.3 RAC systems. I ran a query similar to below to get more information: select sid, serial#, program, module, action, username, osuser, sql_hash_value, machine, event, blocking_session from v$session where status='ACTIVE'; About 1 out of 5 times this query hangs. When it hangs, it waits for exactly 60 seconds on "DIAG idle wait" and then returns the result set. If I remove the blocking_session column, this query runs fine and never hangs. Has anyone run into this or have any ideas why this would happen?