Understanding High Object Copy Times

Jenny Zhang yu.zhang at oracle.com
Thu Apr 27 23:58:39 UTC 2017


Hi, Hezih,

It seems this workload is very heavy on Remember Set. It has about 31G 
native memory for RSet (old gen) and still with coarsening.

What is you pause time goal? The default (200ms) might be too small for 
you.  Can you increase that so G1 can increase the young gen size? Since 
there is not much promotion, I guess most of the object copy time is 
dealing with the Remember Set.

There are other things you can try, like increase the 
G1RSetReginEntries, but the memory footprint will be bigger.

So if you can, I suggest increase the pause time goal first.

Thanks

Jenny



On 4/27/2017 9:22 AM, nezih yigitbasi wrote:
> Hi,
> We see huge object copy times (and relatively high termination times) 
> during young GCs in our production system running on 
> Java 1.8.0_112-b15. You can find the GC logs here: 
> https://gist.github.com/nezihyigitbasi/1f7a92da7860908a611cb1197bd8626b
>
> The young GC times start going high after the timestamp 
> "2017-04-26T03:07:22.164-0700".
>
> I will appreciate if you can give some details about:
> - what goes into the "Object Copy" phase during young GCs and how we 
> can reduce it.
> - why we see high Termination times and what we can do about it
>
> Thanks,
> Nezih



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