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PermGen problems with Lift and Jetty

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

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Joe Avatar asked Sep 20 '09 18:09

Joe


People also ask

What causes PermGen space error?

lang. OutOfMemoryError: PermGen Space is a runtime error in Java which occurs when the permanent generation (PermGen) area in memory is exhausted. The PermGen area of the Java heap is used to store metadata such as class declarations, methods and object arrays.

Is PermGen garbage collected?

The PermGen is garbage collected like the other parts of the heap. The thing to note here is that the PermGen contains meta-data of the classes and the objects i.e. pointers into the rest of the heap where the objects are allocated.

Is PermGen removed in Java 8?

Due to the above problems, PermGen has been completely removed in Java 8. In the place of PermGen, a new feature called Meta Space has been introduced. MetaSpace grows automatically by default. Here, the garbage collection is automatically triggered when the class metadata usage reaches its maximum metaspace size.

How can you control size of PermGen space?

To fix it, increase the PermGen memory settings by using the following Java VM options. -XX:PermSize<size> - Set initial PermGen Size. -XX:MaxPermSize<size> - Set the maximum PermGen Size. In the next step, we will show you how to set the VM options in Tomcat, under Windows and Linux environment.


2 Answers

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.

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VonC Avatar answered Sep 26 '22 14:09

VonC


If you see this when running mvn jetty:run, set the MAVEN_OPTS.

For Linux:

export MAVEN_OPTS="-XX:+CMSClassUnloadingEnabled -XX:PermSize=256M -XX:MaxPermSize=512M" mvn jetty:run 

For Windows:

set "MAVEN_OPTS=-XX:+CMSClassUnloadingEnabled -XX:PermSize=256M -XX:MaxPermSize=512M" mvn jetty:run 

Should be fine now. If not, increase -XX:MaxPermSize.

You can also put these permanently to your environment.

  • For Linux, append the export line to ~/.bashrc

  • For Windows, press Win-key + PrintScreen, and go Advanced > Environment. See also http://support.microsoft.com/kb/310519.

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Ondra Žižka Avatar answered Sep 23 '22 14:09

Ondra Žižka