How to clear PermGen space Error in tomcat

The PermGen space is what Tomcat uses to store class definitions (definitions only, no instantiations) and string pools that have been interned. From experience, the PermGen space issues tend to happen frequently in dev environments really since Tomcat has to load new classes every time it deploys a WAR or does a jspc (when you edit a jsp file). Personally, I tend to deploy and redeploy wars a lot when I’m in dev testing so I know I’m bound to run out sooner or later (primarily because Java’s GC cycles are still kinda crap so if you redeploy your wars quickly and frequently enough, the space fills up faster than they can manage).

This should theoretically be less of an issue in production environments since you (hopefully) don’t change the codebase on a 10 minute basis. If it still occurs, that just means your codebase (and corresponding library dependencies) are too large for the default memory allocation and you’ll just need to mess around with stack and heap allocation. I think the standards are stuff like:

-XX:MaxPermSize=SIZE

I’ve found however the best way to take care of that for good is to allow classes to be unloaded so your PermGen never runs out:

-XX:+CMSClassUnloadingEnabled -XX:+CMSPermGenSweepingEnabled

Stuff like that worked magic for me in the past. One thing tho, there’s a significant performance tradeoff in using those, since permgen sweeps will make like an extra 2 requests for every request you make or something along those lines. You’ll need to balance your use with the tradeoffs.

You have to allocate more space to the PermGenSpace of the tomcat JVM.

This can be done with the JVM argument : -XX:MaxPermSize=128m

By default, the PermGen space is 64M (and it contains all compiled classes, so if you have a lot of jar (classes) in your classpath, you may indeed fill this space).

On a side note, you can monitor the size of the PermGen space with JVisualVM and you can even inspect its content with YourKit Java Profiler