Perf Impact of CMSClassUnloadingEnabled
Andreas.Loew at oracle.com
Tue Nov 8 08:13:58 PST 2011
many thanks for your reply :-)
The behavior you mention indeed seems a little "unfortunate"... ;-)
Will this change as part of the efforts to completely remove PermGen
(part of the "HotRockit" initiative) following the example of JRockit?
Thanks again & best regards,
Senior Java Architect
Oracle Advanced Customer Services Germany
Am 08.11.2011 16:58, schrieb Jon Masamitsu:
> Hotspot maintains a list of classes that are loaded in the
> Dictionary (dictionary.hpp/cpp). This list does not keep
> classes alive. After marking (when we know what classes
> are dead), we walk the list and remove dead classes.
> Hotspot does not keep information that says classes have
> not been unloaded, so the list is always walked.
> On 11/07/11 10:33, Andreas Loew wrote:
>> Hi Jon,
>> sorry, a follow-up question from my side: As it shouldn't be the most
>> normal thing even for a Java EE app to constantly dereference
>> classloaders or single classes that need to be GC'ed:
>> In how far does your statement about increased remark pauses still
>> apply in case the PermGen / set of loaded classes has stayed
>> completely constant between initial mark and remark (which should be
>> the usual case)?
>> And wouldn't there a also be a distinction between PermGen and Old Gen?
>> Many thanks & best regards,
>> Andreas Loew
>> Senior Java Architect
>> Oracle Advanced Customer Services Germany
>> Am 07.11.2011 16:44, schrieb Jon Masamitsu:
>>> Doing class unloading with CMS will often increase the remark pause
>>> and so is not on by default.
>>> On 11/5/2011 3:29 PM, Martin Hare Robertson wrote:
>>>> I recently encountered an interesting GC issue with a Tomcat
>>>> application. I
>>>> came up with a simple repro scenario which I posted to StackOverflow:
>>>> To solve this issue I have been encouraged to use
>>>> I currently use the following GC configuration.
>>>> Is enabling CMSClassUnloadingEnabled likely to have a negative perf
>>>> If not, why is it disabled by default?
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