[opencms] [opencms-dev] Optimizing OpenCMS performance.

[justin.spies at sbcglobal.net]

Sorry Nigel, I just started using this SBC account and didn't see these getting stuck in my spam folder until now...

To answer your question about the garbage collection issues, I've still seen many posts about garbage collection in Java 1.5.  In fact, there is a known garbage collection bug in JDK1.5 that is not scheduled to be fixed until 1.5_08.

Also, despite the performance improvements (I've read of people using 12GB heap sizes on 64bit machines, but have no way to verify this), the system still spends a large amount of time processing the memory.  I'm working on a project now that involves a BEA server using the Sun 1.4 JDK and a full GC of a 400MB heap is still taking about 1.0 - 1.5 seconds.  From what I've read, there are two approaches to tuning GC--the first is to setup the system to perform frequent, but short (low pause) collections (i.e. using a small heap) and the other is to tune the system using infrequent but long collections (i.e., using a large heap.)  The route taken depends on the application.

Justin

----- Original Message ----
From: Nigel Kersten <nigel at cofa.unsw.edu.au>
To: The OpenCms mailing list <opencms-dev at opencms.org>
Sent: Friday, June 16, 2006 7:32:28 AM
Subject: Re: [opencms] [opencms-dev] Optimizing OpenCMS performance.


On 16/06/2006, at 9:24 PM, <justin.spies at sbcglobal.net>  
<justin.spies at sbcglobal.net> wrote:

> Having such a large VM configured can cause garbage collection  
> issues, which lead to performance problems.  I'm not sure that is  
> the problem here, however to find out, you can use the following VM  
> options:
>
> -verbose:gc -XX:+PrintGCTimeStamps -XX:+PrintGCDetails -Xloggc:"C: 
> \garbage.log"
>
>
> Obviously you'll want to change the -Xloggc: value to a file that  
> matches one on your file system.  With as large of a VM as you  
> have, it is possible that the system is causing long pauses to  
> collect a large amount of garbage objects.  Look for entries where  
> the system does a full garbage collection and note how long they  
> take and how far apart they are spaced.

Thank you very much Justin.

I had come across mention of this, but also that garbage collection  
issues like this shouldn't be a problem with Tomcat 5.5 and Java 1.5,  
does that seem right to you?

I did test with a wide range of max values, and this cpu usage issue  
cropped up irrespective of those settings.

Thanks for the debug info, I'll grab that.

-- 
Nigel Kersten [Senior Technical Officer]
College of Fine Arts, University of NSW, Australia.
CRICOS Provider Code: 00098G




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