PermGen Collection Issues

[Martin Hare-Robertson]

>> I am hitting a "java.lang.OutOfMemoryError: PermGen space" in a situation
>> where I think a great deal of the perm gen is actually eligible for
>> collection.
>
>By default CMS does not collect classes; try with
>-XX:+CMSClassUnloadingEnabled.

Running with -XX:+CMSClassUnloadingEnabled improved the results as Tomcat survived 58 webapp reloads (compared to 30 without CMSClassUnloadingEnabled) before hitting the same endless (Permanent Generation Full/Last ditch collection) GC issues and throwing "OutOfMemoryError: PermGen space".

>> I am running Tomcat 6 using a 32 bit Hotspot JVM (1.6.0_07). I have had
>
>Those are fairly old too. Also note that just because your app code does
>not leak, many (badly written) libraries keep static state or hidden
>internal threads alive unless they are explicitly shut down/cleaned up.

The heap dumps which I have taken should reveal if any libraries are doing anything to keep old webapp classloaders alive. According to Eclipse MAT the only path to a GC root for the old classloaders is through weak references.

Is there anything else I could try to fix this? Is it possible that this is a JVM/GC bug?