We are running Tomcat 5.5.27 on Linux 2.6.18-53.1.4.el5xen (Red Hat
4.1.2-14) with Java 1.6.0_05 (32 bit) in a Xen virtualization
environment (not my server, so unsure what version that is). It has 3
webapps running, two of ours and Tomcat's manager.
Normally, when we run 'top', Java and it's related PG 8.3.3 database
that drives the Tomcat webapps show very low CPU utilization (0-1%) and
even leave the 'top' listing. When there is higher user activity, we
see Java increase to 4-20% utilization, but these are spikes that also
tend to return to the low utilization shortly after the burst. We run
Java with options: -server -Xms2200m -Xmx2200m -XX:MaxPermSize=128m.
But every so often, Java "goes crazy" and reaches 95-99% CPU
utilization, and it sticks there, even though there is little Tomcat
activity. What is unusual to me is that during this initial phase of
high CPU utilization, the webapps themselves appear to run smoothly
(don't really notice a slowdown like you'd expect from such high
utilization), logging in, using the web interface, doing queries,
updates, etc. Also, the tomcat access log show little actual user
activity while it's running so busy.
Unfortunately, after some time, it seems that Tomcat eventually locks up
and we have to restart the system, where the process repeats itself:
initially normal low utilization, followed by 99% utilization with the
system still working okay, followed by a lock-up and restart.
So it seems like there's a Java thread that is running amok, yet not a
critical thread (at least not initially) since the apps appear to be
working fine.
How best can I find the troubled thread on a running production system?
Thanks,
David
P.S. Note that our webapps run on lots of servers in a similar
configuration (albeit without Xen) and we've never seen this before
after years of running production systems -- it's just this one system.
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