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From "Moore, Jon, Vodafone UK" <Jon.Mo...@vodafone.com>
Subject RE: java.lang.OutOfMemoryError: PermGen space
Date Fri, 21 Oct 2016 07:46:22 GMT
Thanks Chris. (and to everyone else who has replied)

Yes I am a novice at Java as well. I support the IVR system that points to the application
servers and have ended up trying to resolve this issue as our developers of the applications
can't help.

The way we are told on the training to deploy the application in the IVR is to use the deploy/un-deploy
options in tomcat manager. I have also seen a colleague make a copy of the applications war
file away from its normal folder (webapps), stop the tomcat Windows service, delete the applications
deployed folder and restart the tomcat windows service to re-deploy the application.

I have tried to run the commands you suggested from a CMD box but nothing gets outputted.

Regards

Jon Moore 

-----Original Message-----
From: Christopher Schultz [mailto:chris@christopherschultz.net] 
Sent: 20 October 2016 17:40
To: Tomcat Users List
Subject: Re: java.lang.OutOfMemoryError: PermGen space

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Jon,

On 10/20/16 6:00 AM, Moore, Jon, Vodafone UK wrote:
> I have a problem where our customers application server stops working 
> intermittently and when we check the Tomcat logs we get the message " 
> java.lang.OutOfMemoryError: PermGen space" but the Tomcat service is 
> still running, and we have to restart the Tomcat service. I am a 
> complete novice when it comes to Tomcat but am expected to resolve 
> this issue as this server is part of the Avaya telephony solution.
> 
> I have 2 questions please.
> 
> 1 - What would be causing this.

Are you also a Java novice as well? No judgement... I just want to adjust my level of snark
appropriately :)

Java has a special heap space called the "permanent generation" (a term which becomes less
descriptive as time goes on) but basically all java.lang.Class objects loaded by the JVM go
there. The more libraries and other stuff that gets loaded, the more space in permgen is used.
The defaults for the size of permgen are often fairly small, and you may have to raise them.
This is especially true for applications that use large frameworks like Spring.

Raising the permgen space is almost always the right decision under normal circumstances when
you get an OOME:permgen error. I would double whatever its current value is and monitor the
application for a while to see if that improves things.

The only situation I know of where raising the permgen size is not the right move is when
there is a "classloader-pinning leak". That happens when you hot-deploy an application many
times, but the old versions of the application are not undeploying cleanly. This situation
is quite the rabbit-hole, so I'll stop there unless you can confirm that you do hot-deployments
without restarting Tomcat and the JVM.

If you instead get OOME for other reasons, it's frequently NOT the right decision to increase
the heap size because it usually indicates that there is a memory leak in the application
and giving it more heap just means you'll wait longer between failures. Instead, the application
should be fixed to not leak memory :)

> 2 - What are the default Java memory settings for Initial memory pool, 
> maximum memory pool size and thread stack size when the fields are 
> blank when you use the "Configure Tomcat" interface on Windows. I was 
> wondering if changing one or more of these settings would help ?

The default depends upon the JVM and the OS.

> We are running Tomcat 6.0.26 on Windows Server 2008 R2 standard and 
> JVM version is 1.6.0_20-b02

Best way to find out for sure[1] is:

C:\> java -XX:+PrintFlagsFinal -version 2>&1 | findstr HeapSize

The two settings you are looking for are MaxHeapSize and InitialHeapSize. Those values are
in bytes, so you'll probably have to divide by 1024 a couple of times to get at the "real"
value in human-readable terms.

The best way to find the default permgen size is:

C:\> java -XX:+PrintFlagsFinal -version 2>&1  | findstr PermSize

Hope that helps,
- -chris

[1]
http://stackoverflow.com/questions/2915276/what-is-the-default-maximum-h
eap-size-for-suns-jvm-from-java-se-6
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