The Java/Tomcat PermGen Problem

Running the project on Tomcat, I find that it gets slower and slower, until it grinds to a halt. Java does not bother to garbage collect class definitions, as they are not expected to change much once a project is running. However, running JRuby, that is not the case, and new classes are being generated on the fly all the time. Consequently, the JVM runs out of memory (what it calls PermGen memory), and everything stops.

The solution appears to be modifying start-up options in the JVM. This can be done by running tomcat6w.exe (on Windows anyway), going to the Java tab, and adding these options:

-XX:+UseConcMarkSweepGC
-XX:+CMSClassUnloadingEnabled
-XX:+CMSPermGenSweepingEnabled

Whether this is a solution remains to be seen, but I am giving it a go.
See also
http://docs.oracle.com/cd/E13209_01/wlcp/wlss30/configwlss/jvmgc.html
http://stackoverflow.com/questions/3334911/what-does-jvm-flag-cmsclassunloadingenabled-actually-do/3334954#3334954