RFC: JEP: Remove the Concurrent Mark Sweep Garbage Collector

[Roman Kennke]

+1 (my questions too)

Plus, so far nobody has actually come forward and expressed interest in actually maintaining CMS.

Roman


Am 8. August 2019 19:33:08 MESZ schrieb Claes Redestad <claes.redestad at oracle.com>:
>Hi Kirk,
>
>sorry for barging in, but this genuinely piqued my interest.
>
>On 2019-08-08 18:37, Kirk Pepperdine wrote:
>> Hi Thomas,
>> 
>> "n the meantime the Oracle garbage collection team introduced a new
>garbage collector, ZGC, and Red Hat contributed the Shenandoah
>collector. Oracle further improved G1, which has been its designated
>successor since initial introduction in JDK6u14, to a point where we
>believe there is little reason to use the CMS collector in
>deployments.”
>> 
>> I fear my experience in tuning GC 1000s of JVMs leaves me at odds
>with the premise that there is little reason to use CMS. In my
>experience CMS overheads are no where near the level of those seen with
>G1. This is not just my experience but there are other organizations
>that have reached the same conclusion. Further more, with the removal
>of CMS we are now recommending that customers consider Parallel GC as
>it offers a far better experience than G1. Again, I’m not alone is
>seeing this as a growing trend.
>
>Which JDK version were these JVMs running? I'm curious if/how you've
>taken into account the tuning work and improvements made to G1 in
>recent releases in your assessments.
>
>> 
>> Although I do have high hopes for both ZGC and Shenandoah, they are
>not an option for most sites at this point in time. I would suggested
>that depreciation of CMS was premature as there was no viable
>alternative. I would further suggest that removal is also premature as
>there is still no viable alternative for the majority of workloads that
>work exceptionally well with CMS.
>
>Can you clarify why they aren't options at this point in time? Or why
>you think they still won't be once CMS is actually removed, be it from
>JDK 14 or a later release?
>
>Thanks!
>
>/Claes
>
>> 
>> Kind regards,
>> Kirk Pepperdine
>> 
>> 
>>> On Aug 3, 2019, at 1:37 PM, Thomas Schatzl
><thomas.schatzl at oracle.com> wrote:
>>>
>>> Hi all,
>>>
>>>   as already discussed during the OCW last week the Oracle garbage
>collection team is set to remove the CMS collector from OpenJDK for the
>reasons stated there and in the JEP in JDK 14.
>>>
>>> I wrote up a first draft available at
>>>
>>> https://bugs.openjdk.java.net/browse/JDK-8229049
>>>
>>> Comments and reviewers to move it along appreciated ;)
>>>
>>> Thanks,
>>>   Thomas
>> 

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