On Mar 26, 2014, at 4:23 PM, Felipe Jaekel <fkjae...@gmail.com> wrote:
> I have configured my Tomcat 7 with the following parameters: > > -Xms4G -Xmx4G -XX:MaxPermSize=256m -XX:+UseTLAB -XX:+UseConcMarkSweepGC > -XX:+CMSClassUnloadingEnabled -Dorg.apache.el.parser.COERCE_TO_ZERO=false > > I've seen in several blogs and StackOverflow posts > that CMSClassUnloadingEnabled should sweep PermGen too, but checking in the > manager application after some undeployments, the PermGen value never > decreases. > > Am I missing something? I'm using OpenJDK 7 update 51 64-bit. > > Thanks Felipe, I spent a lot of time recently troubleshooting this. Here are my observations: > -XX:+UseConcMarkSweepGC This is not necessary. The CMSClassUnloadingEnabled is sufficient. You won't notice PermGen space decrease unless you actually hit the memory ceiling, and then the garbage collector will kick in. There are numerous things that hold soft references to your classes. That's why the PermGen space won't decrease. In addition, Tomcat will incorrectly report memory leaks, because your classes and classloader will be still resident in memory until the GC forces the soft references to release. You must use a profiler (I use YourKit) to really know whether anything is holding hard references to your classes. I found several things that were holding hard references to my classes or threads launched in my applications: * RMI (this was really a pain in the ass to fix, and required a lot of reflective field access to low level JDK stuff). It is very, very difficult to un-export RMI objects cleanly. * Keep-Alive thread, if your web app is initiating HTTP connections * MySQL JDBC driver (not a concern if you load that at the container level, but if you load it inside your webapp, you need to call a static method AbandonedConnectionCleanupThread.shutdown(); Once I fixed these things, I am able to repeatedly reload my application in the Tomcat manager without running out of memory in the PermGenSpace. --Jesse Barnum, President, 360Works http://www.360works.com Product updates and news on http://facebook.com/360Works (770) 234-9293 == Don't lose your data! http://360works.com/safetynet/ for FileMaker Server == --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
