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From James Lampert <>
Subject High CPU usage in Tomcat 7
Date Wed, 20 Jun 2012 16:27:47 GMT
We just had a report of extremely high CPU usage from the Tomcat job on 
one of our customer installations. A WRKACTJOB screen shot from before 
we forcibly shut Tomcat down and restarted it shows:

Subsystem/Job   Type  CPU %  Function        Status
   CATALINA      BCH      .0  CMD-QSH         TIMW
   QP0ZSPWT      BCI   112.2  JVM-org.apache  TIMW
(QP0ZSPWT being the system-generated job that's doing the actual work 
for the CATALINA job.)

Of particular interest is that, at least at the moment the screen shot 
was taken, the QP0ZSPWT job was taking up what appears to be more than 
an entire processor, even though it's in a "time-wait" state.

Based on a Google search on "tomcat 7 high cpu usage," I'm suspecting a 
previously unknown tightloop in our application (which was what I 
suspected even before I did the Google search). The pages I looked at 
also said something about profiling and thread dumps, to find the 
offending thread, but since the job has been terminated and restarted, 
and is not currently malfunctioning, I wouldn't be able to do so even if 
I knew how (which at present I don't).

I've passed on the log files generated by our application itself to 
someone better equipped to deal with them than I, and I've asked the 
Java-400 List at about AS/400-specific steps to track down 
the offending thread if the problem is observed again, but I would also 
value any insights this list might offer.


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