PermGen problems with Lift and Jetty

Question

I'm developing on the standard Lift platform (maven and jetty). I'm repeatedly (once every couple of days) getting this:

Exception in thread "7048009@qtp-3179125-12" java.lang.OutOfMemoryError: PermGen space
2009-09-15 19:41:38.629::WARN:  handle failed
java.lang.OutOfMemoryError: PermGen space

This is in my dev environment. It's not a problem because I can keep restarting the server. In deployment I'm not having these problems so it's not a real issue. I'm just curious.

I don't know too much about the JVM. I think I'm correct in thinking that permanent generation memory is for things like classes and interned strings? What I remember is a bit mixed up with the .NET memory model...

Any reason why this is happening? Are the defaults just crazily low? Is it to do with all the auxiliary objects that Scala has to create for Function objects and similar FP things? Every time I restart Jetty with newly written code (every few minutes) I imagine it re-loads classes etc. But even so, it cant' be that many can it? And shouldn't the JVM be able to deal with a large number of classes?

Cheers

Joe

Answer 1

From this post:

This exception occurred for one simple reason :
the permgenspace is where class properties, such as methods, fields, annotations, and also static variables, etc. are stored in the Java VM, but this space has the particularity to not being cleaned by the garbage collector. So if your webapp uses or creates a lot of classes (I’m thinking dynamic generations of classes), chances are you met this problem. Here are some solutions that helped me get rid of this exception :

• -XX:+CMSClassUnloadingEnabled : this setting enables garbage collection in the permgenspace
• -XX:+CMSPermGenSweepingEnabled : allows the garbage collector to remove even classes from the memory
• -XX:PermSize=64M -XX:MaxPermSize=128M : raises the amount of memory allocated to the permgenspace

May be this could help.

Edit July 2012 (almost 3 years later):

Ondra Žižka comments (and I have updated the answer above):

JVM 1.6.0_27 says: Please use:

• CMSClassUnloadingEnabled (Whether class unloading enabled when using CMS GC)
• in place of CMSPermGenSweepingEnabled in the future

See the full Hotspot JVM Options - The complete reference for mroe.