RE: Unable to detect blocking session

From: Le, Binh T. <>
Date: Wed, 21 Feb 2018 21:07:13 +0000
Message-ID: <>

Try this … Any way … in OEM12 or EMCC 13c .. has session block metric that you can set …. Then … you can let corrective action wait for 15 minutes or something .. then kill

  • Find lock and kill ------------------------------ select vs.username lock_user, vs.osuser lock_os_user, vh.sid || ' <-- he is locking' locking_sid , vs.status lock_status, vs.module lock_module, vs.program program_holding, jrh.job_name lock_job, vsw.username wait_user, vsw.osuser wait_os_user, vw.sid ||' <-- he is waiting' waiter_sid, vsw.program program_waiting, jrw.job_name wait_job, 'alter system kill session ' || ''''|| vh.sid || ',' || vs.serial# || ',_at_' ||vs.inst_id || ''';' kill_the_lock_command, 'alter system kill session ' || ''''|| vw.sid || ',' || vsw.serial# || ',_at_' ||vsw.inst_id || ''';' kill_the_wait_command from gv$lock vh, gv$lock vw, gv$session vs, gv$session vsw, dba_scheduler_running_jobs jrh, dba_scheduler_running_jobs jrw where (vh.id1, vh.id2) in (select id1, id2 from gv$lock where request = 0 intersect select id1, id2 from gv$lock where lmode = 0) and vh.id1 = vw.id1 and vh.id2 = vw.id2 and vh.request = 0 and vw.lmode = 0 and vh.sid = vs.sid and vw.sid = vsw.sid and vh.sid = jrh.session_id(+) and vw.sid = jrw.session_id(+);

From: [] On Behalf Of Sandra Becker Sent: Wednesday, February 21, 2018 3:07 PM To: Powell, Mark <> Cc: oracle-l <> Subject: Re: Unable to detect blocking session

***This email is from an external source. Only open links and attachments from a Trusted Sender.*** New information: we didn't actually find the blocker using v$lock (or gv$lock). Someone finally looked at gv$session and saw that a sqlplus session had been idle for over an hour during the timeframe the application was experiencing issues. We had a script, below, that we were using to locate the root blocker since we have an application issue we're also trying to resolve. That script did NOT show the sqlplus session that appeared to be the blocker. We think that session was the blocker because as soon as the user exited the session, everything cleared almost immediately. We're trying to figure out a script that will find the root block, including sessions like this user's that ran an update statement, but didn't actually update any rows and he didn't do a commit. If someone has any suggestions, we would definitely like to hear them.


        b.username||' - '||b.blocker_sid||','||b.blocker_sess_serial#||',_at_'||b.inst_id||' : '||b.sql_id blocker, b.seconds_in_wait b_secs,
        w.username||' - '||w.sid||','||w.sess_serial#||',_at_'||w.inst_id||' : '||w.sql_id waiter, w.seconds_in_wait w_secs
      FROM gv$session_blockers bb
           JOIN gv$session sb
                ON bb.blocker_sid = sb.sid
                AND bb.blocker_sess_serial# = sb.serial#
     ) b
        sw. sql_id,
      FROM gv$session_blockers bw
           JOIN gv$session sw
                ON  bw.sid = sw.sid
                AND bw.inst_id = sw.inst_id
                AND bw.sess_serial# = sw.serial#
     ) w
        ON b.blocker_sid = w.blocker_sid
ORDER BY w.seconds_in_wait DESC

On Wed, Feb 21, 2018 at 12:14 PM, Powell, Mark <<>> wrote:

Sandy, to add to what Rick's reply, the "SQL*Net message from client" indicates to me the user made an update and failed to commit it. I think Rick provided valid possibilities for EM but for why you could not directly query the information I think we would need to see what queries you used to try to find the blocker though from your final remarks you did use GV$LOCK and GV$SESSION plus sys.dbms_lock_allocated to find the blocker. Could the earlier attempt have been using the V$ version and so missed the blocker since it was on another instance? The sys.dbms_lock_allocated table would not be necessary to find the blocking session though it would identify which User Lock (UL) was involved if a UL was involved.

Mark Powell
Database Administration
(313) 592-5148<tel:(313)%20592-5148>

From:<> <<>> on behalf of Sandra Becker <<>> Sent: Wednesday, February 21, 2018 10:32:14 AM To: oracle-l
Subject: Unable to detect blocking session

Oracle EE on RHEL 5.11

We had a situation in our production environment yesterday where a user had a sqlplus session had an uncommitted "zero row" update on a table. This kept the actual application from processing orders using that same table. The sqlplus session was initiated from SQL*Plus Release The wait event on the application session was holding a user lock, which was apparently blocked, with a wait event of "SQL*Net message from client". Once the user's sqlplus session was exited, all application sessions resumed normal functions without any intervention. The user who issues the update is a tier1 support person, so we can't lock out their access for such activites to prevent future occurrences.

What we are trying to understand is why we were unable to see that the user's sqlplus session was blocking either through EM or through queries looking at gv$session and gv$session_blockers. We found the application locks by joining gv$lock, gv$session and sys.dbms_lock_allocated. Any ideas why we could see the blocking or suggestions on what we can look at so we don't miss it again?


Sandy B.


Sandy B.
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-- Received on Wed Feb 21 2018 - 22:07:13 CET

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