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Posted to users@tomcat.apache.org by Ondrej Zizka <xz...@stud.fit.vutbr.cz> on 2007/01/18 03:19:05 UTC
Tomcat PermGen OutOfMemoryException solution?
Hello,
I have the common problem with PermGen and Tomcat, see
http://mail-archives.apache.org/mod_mbox/tomcat-users/200606.mbox/%3C44858185.3040009@kerbtier.ch%3E
Suppose there is a school server where students (re)deploy their apps, each
of which's classes definitions take about five to ten MB.
Now we have dozens of students, who will deploy at least once, but rather
several times a day. That means the server has to be restarted every few
hours.
There is no way to automatically flush the PermGen somehow? Or, under which
conditions can the GC collect undeployed app's classes data?
Thanks, Ondra Zizka
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RE: Tomcat PermGen OutOfMemoryException solution?
Posted by "Caldarale, Charles R" <Ch...@unisys.com>.
> From: Christopher Schultz [mailto:chris@christopherschultz.net]
> Subject: Re: Tomcat PermGen OutOfMemoryException solution?
>
> > There is no way to automatically flush the PermGen somehow?
> > Or, under which conditions can the GC collect undeployed
> > app's classes data?
>
> I'm pretty sure you can't do that unless you write some JNI code,
> and you might not even be able to do it even then.
You can't. Before an OOME is presented, the JVM has already cleaned out
the PermGen of any dead instances of java.lang.Class.
This is a pretty decent survey of several reasons why classes can't be
GC'd:
http://opensource.atlassian.com/confluence/spring/pages/viewpage.action?
pageId=2669
- Chuck
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Re: Tomcat PermGen OutOfMemoryException solution?
Posted by Christopher Schultz <ch...@christopherschultz.net>.
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Ondrej,
Ondrej Zizka wrote:
> Suppose there is a school server where students (re)deploy their apps, each
> of which's classes definitions take about five to ten MB.
> Now we have dozens of students, who will deploy at least once, but rather
> several times a day. That means the server has to be restarted every few
> hours.
I was recently taken to task for asserting that Java holds on to
outdated java.lang.Class objects even after the ClassLoader is
discarded. (This might happen when a webapp is reloaded).
It turns out that I'm an old war horse and that problem was fixed a very
long time ago.
If you are having memory problems it is more likely that one of the
following is occurring:
1. You have one or more misbehaving webapps (they are retaining memory
longer than they should).
2. You are running a very old and/or buggy version of Java
and/or Tomcat.
3. The webapp reload procedure is not working as you expect.
4. You have tons of libraries that are being individually reloaded
by each web application. Take the advice of your article and
provide shared versions of many popular libraries.
> There is no way to automatically flush the PermGen somehow? Or, under which
> conditions can the GC collect undeployed app's classes data?
I'm pretty sure you can't do that unless you write some JNI code, and
you might not even be able to do it even then.
Another poster suggested that you have your students setup their own
Tomcat environments. I completely agree ;)
- -chris
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Re: Tomcat PermGen OutOfMemoryException solution?
Posted by Roger Keays <ro...@ninthavenue.com.au>.
Ondrej Zizka wrote:
> Hello,
>
> I have the common problem with PermGen and Tomcat, see
> http://mail-archives.apache.org/mod_mbox/tomcat-users/200606.mbox/%3C44858185.3040009@kerbtier.ch%3E
>
> Suppose there is a school server where students (re)deploy their apps, each
> of which's classes definitions take about five to ten MB.
> Now we have dozens of students, who will deploy at least once, but rather
> several times a day. That means the server has to be restarted every few
> hours.
>
> There is no way to automatically flush the PermGen somehow? Or, under which
> conditions can the GC collect undeployed app's classes data?
How about having them each install their own Tomcat locally? It'd be
part of the learning experience :)
>
> Thanks, Ondra Zizka
>
>
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>
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