Future of CMS

Jon Masamitsu jon.masamitsu at oracle.com
Sat Jun 11 21:42:13 UTC 2016

On 6/11/2016 1:56 AM, kirk at kodewerk.com wrote:
> Hi Jon,
> I question that the current implementation of G1 is better than CMS. Though I do try to move my clients to G1, there are still many cases where I can get much less GC interference with CMS than I can with the G1. I can look into sending you side by side GC logs if you are interested in a visualization. At the very least I can send you contrasting Censum screenshot.


We're identified use cases where CMS still out performs G1 and have been
working to make G1 better in those cases.   As the JEP says G1 might not
out perform CMS in every case but G1 is going to get better and better in
many different ways whereas CMS will not (at least by Oracle's hand).
My expectation is that the weight of all the improvements to G1 will
in the end make it the more attractive collector.


> Kind regards,
> Kirk Pepperdine
>> On Jun 11, 2016, at 3:35 AM, Jon Masamitsu <jon.masamitsu at oracle.com> wrote:
>> Added hotspot-gc-dev.
>> On 6/10/2016 6:17 PM, Jon Masamitsu wrote:
>>> Jungwoo, Ramki, Tony (and other friends of CMS),
>>> I wanted to be sure you guys saw this JEP.
>>> Deprecate the CMS garbage collector (UseConcMarkSweepGC).
>>> http://openjdk.java.net/jeps/8142518
>>> I know you do development on CMS and wanted to know if
>>> had thoughts about the future of CMS.
>>> At some point Oracle is going to stop supporting CMS.
>>> The burden of testing and maintaining the CMS code doesn't
>>> make much sense given that we think G1 is the better
>>> collector.    If we deprecate CMS in jdk9, support would be dropped
>>> no earlier than jdk10.
>>> Have you guys talked about what you would like to do with regard
>>> to continuing CMS development without Oracle's help?
>>> I've been told that if CMS exists in the Oracle binaries, then
>>> customers will expect it to work.  So not supporting CMS
>>> means it is not in the build.
>>> Jon

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