JEP 173: Remove Rarely-Used Combinations of Garbage Collectors

Thomas Viessmann thomas.viessmann at oracle.com
Thu Dec 6 23:39:44 PST 2012


Hi all,


two comments from my side. I work in support and have tuned about 50 
applications
in the past decade. My experience with iCMS was not as good as Kirk's. 
Actually I've
never come across a scenario where iCMS could beat regular CMS. At least 
not on
big server systems. CMS always gave better results, either by 
configuring sufficiently
big eden/survivors or, surprisingly, by configuring instant promotion 
(small eden, no survivors).

Maybe from an engineering/testing perspective GC consolidation is a good 
idea. On the other hand
we in support have seen lots of bugs and crashes in the GC space. It was 
very helpful that
we could offer our customers choices to work around. E.g. temporarily 
replace CMS by iCMS
or parallel with serial. Keep that in mind please.

Thanks and Regards

Thomas



I've come
On 12/07/12 00:35, Bernd Eckenfels wrote:
> Am 06.12.2012, 23:10 Uhr, schrieb Kirk Pepperdine <kirk at kodewerk.com>:
>
>> I appreciate the desire to remove unneeded code from the JVM. I think 
>> you are right... in the cases where I did move customers to the 
>> serial collector I could have just as easily tuned the parallel 
>> collector down So, getting rid of serial wouldn't be seen as a loss 
>> in my books.
>
> Actually it would be a very big win for CMS, but before the code can 
> be removed the ParallelOld needs to be CMS enabled. So I guess it is 
> harder to remove the actual code, but at least it can be removed from 
> some of the other GC combinations.
>
> The question is, if a serial single threaded GC is not needed for some 
> reference purposes, correctness proofs or similiar?
>
> Gruss
> Bernd

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