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 Midrange.com 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.
--
JHHL
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