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I keep getting a "PermGen" error on my Tomcat 6 server.

I know what application is causing the problem, but I am not sure why it is doing so. The application is using MySQL 5 and running on JDK 6.

Are there any tools/suggestions to diagnosis or analyze the underlying issue(s) with the specific application?

Thanks

Berek Bryan
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  • Is this problem any different than the one [described here](http://stackoverflow.com/questions/1124131/what-can-be-done-with-permgen-out-of-space-exception-in-tomcat-spring-hibernate)? – Tim Post Feb 24 '11 at 15:01
  • I recommend reading [this article](http://plumbr.eu/blog/what-is-a-permgen-leak) (written by me), to better understand why these errors can happen. And it contains some suggestions for solving them as well. – Nikem Jul 12 '12 at 12:50

6 Answers6

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The PermGen is used to store class definitions and the interned string pool. Your code could be filling it (if it calls intern needlessly), but more likely is that the default is undersized for your application.

This is because Tomcat will load new classes every time you deploy a WAR -- or, if you are working in a development environment, every time you edit a JSP. Those should eventually get cleaned up, but in an active development environment you can have periods where there are both old and new instances loaded. Or, if you're in a production environment and have a large web-app, you might simply need more space.

To set the permgen size, use -XX:MaxPermSize=SIZE

The following links may be helpful: tuning GC (this is the 1.5 edition), GC FAQ (1.4.2 edition), Hotspot VM options (I believe this is 1.6)

kdgregory
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  • Since this got touched today (thanks, to whoever upvoted), here's another link on diagnosing OOM (written by me): http://www.kdgregory.com/index.php?page=java.outOfMemory – kdgregory Dec 03 '09 at 13:38
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Try the following JVM switches: 

-XX:+UseConcMarkSweepGC
-XX:+CMSPermGenSweepingEnabled
-XX:+CMSClassUnloadingEnabled

Upping the permgen space with -XX:MaxPermSize just delays the problem.

Please see this comment: How to deal with “java.lang.OutOfMemoryError: PermGen space” error

That indirectly pointed me to these two posts: problem, solution

Community
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opyate
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    It delays the problem if you maintain accidental classloader links. And, to be sure, there are a lot of cases where this can happen, and it can be next to impossible to find them unless you know your libraries inside and out (java.beans.Introspector, for example, maintains a cache of class data). – kdgregory Dec 03 '09 at 13:25
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    However, often the problem is simply that the web-app is too large to use the default. Particularly in a development environment, where you have a 64Mb permgen, and may be redeploying constantly. It takes time for all existing references to go out of scope (for example, a pooled thread hanging onto the last servlet that it ran). – kdgregory Dec 03 '09 at 13:29
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try this : IN Linux Machines

export JAVA_OPTS="-XX:PermSize=128m"

Tvaroh
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Ganesh Tripathi
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I agree that increasing the permgen space with -XX:MaxPermSize just delays the problem. I tried increasing the permgen and after that I started getting the same error after I sent more number of requests to my server. Additional flags like -XX:+CMSClassUnloadingEnabled is suggested even though it will decrease the performance little bit.

Fun With Puzzles
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I think you might have many JSPs in your application. There is a known issue in tomcat where restarting a deployed application with many JSPs causes PermGen issues because tomcat recompiles and reloads all these classes again. Increasing the size as mentioned in the previous post should help.

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I have seen lots of permgen errors when tomcat is reloaded after a code change when using hibernate and spring, I think its due to the logger/ehcache instances not being shut down properly.

Theresa Forster
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