Alfresco: OutOfMemoryError: PermGen space

As already mentioned, you're probably experiencing leaking class loaders. For some reason your classes are not being unloaded. This can happen for two reasons

• Objects of said classes still exist on the heap, objects always reference their class, or
• The class loader is referenced somewhere, for whatever reason, class loaders reference their classes in order to not load them twice

There's no catch-all solution to this problem. One helpful tool to help you find the root cause is the Eclipse Memory Analyzer Tool, which you can apply to a heap dump from your JVM (you can enable heap dumps on OOMs with the -XX:+HeapDumpOnOutOfMemoryError option). Perhaps start looking for java.lang.Class objects from your web app to see why they are being kept alive. Unfortunately, PermGen is not normally part of a JVM heap dump, so you can only try to find correlating artifacts in the rest of the heap (Class-objects are not stored in PermGen if im not mistaken, only the actual byte code is, please correct me if I'm wrong though).

HTH.

Edit:
Dave Cheney suggests in a comment that java.lang.Class-objects are indeed part of PermGen, and not included in a normal hotspot heap dump. Unless you have a JVM which writes this info in the heap dump, you'll need a different approach. You can still look for instances of your objects, but if you're leaking classes/class loaders (they both unfortunately imply each other) it seems you need to look for other signs (meta data objects from JBoss, etc).

i'm afraid there is no clear answer to your question. the most space in the permgen should be occupied by the classes of your application. it is possible your application is generating classes while it is running. then the described behaviour of your application is as expected. when your application is not generating classes on the fly, the number of loaded classes and amount of permgen should be more or less static.

when your application is creating to much classes you can get memory problems. you will then see java.lang.OutOfMemoryError: PermGen space messages in the tomcat log. you can test this by setting the perm gen explicitly with this parameter: -XX:MaxPermSize=.

you can also try this parameter: -XX:+CMSClassUnloadingEnabled with the cms garbage collector. when the number of loaded classes does not go down, you still have references from objects to these classes. this could be a sign you really have a memory leak. but you definitely have to know the running application to be sure. when this is the desired behavior of the application you can only increase the space for the perm gen. the size of the perm gen is additional to the size of the heap.

here is a posting on stackoverflow which suggests a method to make clear what is the content of the permgen.