Dealing with "java.lang.OutOfMemoryError: PermGen space" error
Recently I ran into this error in my web application:
java.lang.OutOfMemoryError: PermGen space
It's a typical Hibernate/JPA + IceFaces/JSF application running on Tomcat 6 and JDK 1.6. Apparently this can occur after redeploying an application a few times.
What causes it and what can be done to avoid it? How do I fix the problem?
The solution was to add these flags to JVM command line when Tomcat is started:
-XX:+CMSClassUnloadingEnabled -XX:+CMSPermGenSweepingEnabled
You can do that by shutting down the tomcat service, then going into the Tomcat/bin directory and running tomcat6w.exe. Under the "Java" tab, add the arguments to the "Java Options" box. Click "OK" and then restart the service.
If you get an error the specified service does not exist as an installed service you should run:
tomcat6w //ES//servicename
where servicename is the name of the server as viewed in services.msc
Source: orx's comment on Eric's Agile Answers.
You better try -XX:MaxPermSize=128M rather than -XX:MaxPermGen=128M .
I can not tell the precise use of this memory pool, but it have to do with the number of classes loaded into the JVM. (Thus enabling class unloading for tomcat can resolve the problem.) If your applications generates and compiles classes on the run it is more likely to need a memory pool bigger than the default.
App server PermGen errors that happen after multiple deployments are most likely caused by references held by the container into your old apps' classloaders. For example, using a custom log level class will cause references to be held by the app server's classloader. You can detect these inter-classloader leaks by using modern (JDK6+) JVM analysis tools such as jmap and jhat to look at which classes continue to be held in your app, and redesigning or eliminating their use. Usual suspects are databases, loggers, and other base-framework-level libraries.
See Classloader leaks: the dreaded "java.lang.OutOfMemoryError: PermGen space" exception, and especially its followup post.
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