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From Quintin Beukes <>
Subject Re: Starting Geronimo with More PermGen
Date Mon, 14 Sep 2009 16:58:01 GMT
I have read about this problem many times, and can never really
understand that if the PermGen is GC'ed how a memory leak can occur
that would cause a crash?

After all, if all references to a Class is cleared it should be GC'ed, right?

My understanding of how these memory leaks occur in these dynamically
loading containers, like app servers (deployment), servlet containers
(deployment), OSGi (bundles), etc. That means the same class is loaded
many times, and sometimes anonymous/embedded classes in them, and
dynamically generated classes (like proxies in Geronimo). Now, if you
undeploy, won't this clear all references to these classes?

Can you give me an example scenario of a real life memory leak which
causes a leak and eventually PermGen OOME.


On Mon, Sep 14, 2009 at 5:06 PM, Kevan Miller <> wrote:
> On Sep 14, 2009, at 10:07 AM, Quintin Beukes wrote:
>> Doesn't Sun have a GC on the PermGen? Or is it just low priority,
>> meaning this won't happen on production servers. Even in a the common
>> production host you deploy a lot. They might be further apart, but
>> they are many none the less. And these servers are usually solid,
>> meaning they don't fall over. I will easily reach 10 deployments
>> without a server restart.
> Yes, PermGen is GC'ed. However, if there is a ClassLoader memory leak, then
> a ClassLoader (and associated classes) can't be GC'ed, even though the
> application has been undeployed.
>> Though on my dev machine I have gone to about 20 deployments (around
>> there - I just counted the log entries from server start while
>> pressing page down the whole time and counted 18) before it gave a
>> permgen. This was in a 2 hour period.
>> If this is going to be a problem, is JRocket expensive?
> I assume that JRockit stores class meta data in heap space. So, just means
> you have more storage for your class meta data, rather than specialized
> PermGen.
> If you recreate your OOME PermGen with -XX:+HeapDumpOnOutOfMemoryError, we
> can help diagnose your problem. One of these days, I'll write a blog on
> this...
> --kevan

Quintin Beukes

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