The response to my post about OutOfMemory PermGen errors in Tomcat with Sun JDK brought up some very interesting things. I learned a lot from Frank Kieviet’s blog about possible classloader memory leaks and jhat usage. One comment brought up that it could be a Tomcat bug and it should be fixed with version 6 so I ran the same test again with Tomcat 6.0.14:

As you can see when restarting the lambdaprobe application and accessing it again and again results in increasing the PermGen memory usage until it the OutOfMemory error occurs. This is the same behavior as with Tomcat 5 – so it seems the problem is not cause by the container.

To be sure that the memory leak is caused by the application I ran the same test with a very small application included in Tomcat: the JSP-examples. Though this application does not contain many classes the memory consumption for loading them is not very much but it should be enough when reloading it a thousand times. Here are the results for Tomcat 5:

and for Tomcat 6, both running on Sun JDK 6:

After running these tests it was clear to that the memory leak is caused by the application. It is no bug in Tomcat or Sun JDK. I will have to take a closer look on our web applications to find out what reference causes this problem. Using a current or patched versions of jhat should allow me to find the problem.