Unable to detect blocking session

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 11.1.0.6.0. 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?

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Sandy B.

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http://www.freelists.org/webpage/oracle-l Received on Wed Feb 21 2018 - 16:32:14 CET