Perf Impact of CMSClassUnloadingEnabled

[Jon Masamitsu]

Doing class unloading with CMS will often increase the remark pause times
and so is not on by default.

On 11/5/2011 3:29 PM, Martin Hare Robertson wrote:
> Hi,
>
> I recently encountered an interesting GC issue with a Tomcat application. I
> came up with a simple repro scenario which I posted to StackOverflow:
> http://stackoverflow.com/questions/8017193/when-does-the-perm-gen-get-collected
>
> To solve this issue I have been encouraged to use
> -XX:+CMSClassUnloadingEnabled.
> I currently use the following GC configuration.
>
> -XX:+UseMembar
> -XX:+UseConcMarkSweepGC
> -XX:+UseParNewGC
> -XX:CMSInitiatingOccupancyFraction=80
> -XX:+UseCMSInitiatingOccupancyOnly
>
> Is enabling CMSClassUnloadingEnabled likely to have a negative perf impact?
> If not, why is it disabled by default?
>
> Thanks
>
> Martin
>
>
>
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