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This was a problem which I faced yesterday. We had a mview refresh which was lagging on one of the server. On checking master site, I found that there were many pending requests coming from the second materialized view site . Checking second site revealed that there were multiple sessions running in database which were waiting on ‘enq :JI Contention’ wait event.
These mviews were being refreshed by job scheduled through a cron. Doing a grep for the refresh script gave following result
$ps -ef|grep scott|grep -v grep
oracle 11725 11714 0 13:00:00 ? 0:00 /usr/bin/sh /home/oracle/cron/Refresh_scott.sh
oracle 19981 19970 0 Feb 7 ? 0:00 /usr/bin/sh /home/oracle/cron/Refresh_scott.sh
oracle 24794 24781 0 06:30:00 ? 0:00 /usr/bin/sh /home/oracle/cron/Refresh_scott.sh
oracle 10538 10527 0 Feb 6 ? 0:00 /usr/bin/sh /home/oracle/cron/Refresh_scott.sh
oracle 13972 13935 0 Feb 6 ? 0:00 /usr/bin/sh /home/oracle/cron/Refresh_scott.sh
oracle 2601 2592 0 19:00:00 ? 0:00 /usr/bin/sh /home/oracle/cron/Refresh_scott.sh
oracle 17274 17246 0 Feb 6 ? 0:00 /usr/bin/sh /home/oracle/cron/Refresh_scott.sh
oracle 8308 8294 0 13:30:00 ? 0:00 /usr/bin/sh /home/oracle/cron/Refresh_scott.sh
This was definitely wrong. I killed the database sessions and also killed the OS processes
$ ps -ef|grep Refresh_scott.sh|grep -v grep|awk ‘{print $2}’|xargs kill -9
This issue had occurred as one more site was added for mview refresh and due to locking issues (while deleting records from Mlog$), job could not complete before next refresh schedule. While scheduling scripts through cron, care should be taken to put a check if script is already running or not. This is required as Cron will spawn the new job (as per job schedule) irrespective of fact that whether earlier execution has completed or not. I used following logic to implement the same check
cnt=`ps -ef|grep Refresh_scott.sh|grep -v grep |wc -l` if [ $cnt -eq 1 ] then echo "Running Fast Refresh now " > $DIR/Check_refresh_scott.log sqlplus /nolog <<EOF > $DIR/Refresh_scott.log conn scott/tiger exec dbms_mview.refresh ... ... exit EOF else echo "Fast refresh already running " > $DIR/Check_refresh_scott.log date >> $DIR/Check_refresh_scott.log exit fi
There could be other logics too which can be used to implement the same. e.g Other could be
filename=$DIR/Check_refresh_scott.log if [ -e $filename ] then echo "Fast Refresh already running " > refresh_runnning.log exit else sqlplus /nolog <<EOF > $DIR/Refresh_scott.log conn scott/tiger exec dbms_mview.refresh ... ... exit EOF rm $filename fi
Other way could be to use DBMS_JOB and DBMS_SCHEDULER to schedule the database job.
