jconsole question -- probably the wrong mailing list but here goes...

[Stephen Ryan]

Hi Alan,
Thanks for that but Im not sure its that at all. I've other servers 
being monitored and Ive never seen jConsole have this effect. I did a 
jmap on the server and saw some huge numbers. Im begining to think that 
theres bad code thats causing classes to be loaded too many times. The 
'Classes' view in jConsole is showing me a constant rise in class 
numbers. I would have  expected this to be more or less stable, 
considering that the server is serving about 4 requests per second. The 
CPU is pretty busy too.Busy  garbage collecting the eden space I guess.

I was considering increasing the eden space to see if that alleavates 
the problem, but if its a code problem, it wont help at all.

Thanks!
Stephen.

Alan Bateman wrote:

> Stephen Ryan wrote:
>
>> Hi,
>>
>> I was wondering if its possible to get the size of the classes loaded 
>> from jConsole. Im seeing a lot of GC's in the Eden Space in a server 
>> thats basically doing nothing. Im thinking that the jvm is trying to 
>> load classes in there that are just too close to the size of that space.
>>
>> Any help appreciated!
>>
>> Stephen.
>
> Classes are essentially allocated from the perm generation so I don't 
> think this is what you are observing. Instead it is likely that you 
> are observing the effect of the JMX agent in the target VM due to the 
> polling by jconsole. Each time jconsole updates the display it must 
> interact with agent in the agent VM so this means some objects are 
> allocated which can lead to periodic scavenging that you observe. You 
> can reduce the polling interval via jconsole's -interval=value option 
> (interval is specified in seconds). The management interface for class 
> loading doesn't include the size of the classes but if you try jstat 
> then you can get this information (jstat -class <vmid>  for example).
>
> -Alan.
>

-- 
Stephen Ryan
Principal QA Engineer

AOL Technologies Ireland Ltd.
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Work: +353 1 4692115

stephen.ryan at corp.aol.com
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