Re: Unable to detect blocking session

From: Powell, Mark <>
Date: Wed, 21 Feb 2018 19:14:57 +0000
Message-ID: <TU4PR8401MB0752123D168C2C81530D84F3CCCE0_at_TU4PR8401MB0752.NAMPRD84.PROD.OUTLOOK.COM>

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

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.

-- Received on Wed Feb 21 2018 - 20:14:57 CET

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