How to clear PermGen space Error in tomcat

Question

I am working in a Windows Environment, and I am getting this error every time I am working with tomcat- ``` Apr 30, 2012 5:30:37 PM org.apache.catalina.core.StandardWrapperValve invoke SEVERE: Servlet.service() for servlet default threw exception java.lang.OutOfMemoryError: PermGen space 2012-04-30 17:30:37.719 INFO net.spy.memcached.MemcachedConnection: Connection state changed for sun.nio.ch.SelectionKeyImpl@4ae53a99 2012-04-30 17:30:37.719 INFO net.spy.memcached.MemcachedConnection: Reconnecting due to failure to connect to {QA sa=localhost/127.0.0.1:11211, #Rops=0, #Wops=0, #iq=0, topRop=null, topWop=null, toWrite=0, interested=0} java.net.ConnectException: Connection refused: no further information Apr 30, 2012 5:30:37 PM org.apache.catalina.core.StandardWrapperValve invoke SEVERE: Servlet.service() for servlet default threw exception java.lang.OutOfMemoryError: PermGen space Exception in thread "Memcached IO over {MemcachedConnection to localhost/127.0.0.1:11211}" java.lang.OutO…

Accepted Answer

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.

How to clear PermGen space Error in tomcat

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