we have a problem with Zimbra network edition. From time to time, "java" process takes 90% of CPU time and 33% of memory.

I did jps and it's this process:

31825 com.zimbra.cs.launcher.TomcatLauncher -Xms709m -Xmx709m -XX:NewRatio=2 -Djava.awt.headless=true -Dcatalina.base=/opt/zimbra/apache-tomcat-5.5.15 -Dcatalina.home=/opt/zimbra/apache-tomcat-5.5.15 -Djava.io.tmpdir=/opt/zimbra/apache-tomcat-5.5.15/temp -Djava.library.path=/opt/zimbra/lib -Djava.endorsed.dirs=/opt/zimbra/apache-tomcat-5.5.15/common/endorsed

Version is 4.5.6, running on Ubuntu.

We have 2GB of memory, 15 users. This "downtime" and high load takes
about five minutes and then continues.

How can I debug this?