G1:long remark pauses

Bengt Rutisson bengt.rutisson at oracle.com
Fri May 16 11:53:07 UTC 2014


Hi again Thomas,


On 2014-05-16 13:34, Thomas Viessmann wrote:
> Hi Bengt,
>
> Sure, the application has lots of objects and references.
> Downsizing the application has been tried The heap size of 24 g is
> already at minimum. A  smaller heap gave OutOfmemory really quick.
> My question was more whether the remark phases could be optimized
> further. I assume this is not the case and we have reached the 
> limitations
> of G1, right?


How many reference objects does the application use? Can you run it with 
-XX:+PrintReferenceGC to see how many there are?

If there are a lot of them I don't think there is much more that can be 
done for the remark phase. But if there are not that many I guess it 
means that the remark phase is inefficient.

Have you tried any of the other GCs? How do they behave with this 
application?

Thanks,
Bengt


>
> Thanks and Regards
>
> Thomas
>
>
>
> On 05/16/14 13:18, Bengt Rutisson wrote:
>>
>> Hi Thomas,
>>
>> On 2014-05-16 13:10, Thomas Viessmann wrote:
>>> Hi Bengt,
>>>
>>> Well, that's already done and it did improve things.
>>> argv[21]: -XX:+ParallelRefProcEnabled
>>> argv[22]: -XX:ParallelGCThreads=48
>>
>> Sorry, I missed that.
>>
>>> before -XX:+ParallelRefProcEnabled was set the stop times were in the range of 20 to 60 seconds.
>>
>> OK. Glad it helped some. :)
>>
>>> The application is a Cacao by Oracle. So they cannot change it.
>>
>> Is there some way of reducing the amount of reference objects that 
>> Cacao uses? Does it have cache sizes or similar that can be tuned. 
>> With a JFR recording we might be able to figure out where the 
>> reference objects come from.
>>
>> Thanks,
>> Bengt
>>
>>> Thanks and Regards
>>>
>>> Thomas
>>>
>>>
>>>
>>>
>>>
>>>
>>> On 05/16/14 12:58, Bengt Rutisson wrote:
>>>>
>>>> Hi Thomas,
>>>>
>>>> It looks like the application is using a lot of Reference objects. 
>>>> The time spent in remark is dominated by reference processing. See 
>>>> the attached graph generated from the log file you sent.
>>>>
>>>> You can try to see if adding -XX:+ParallelRefProcEnabled improves 
>>>> the situation.
>>>>
>>>> If the customer is interested in updating their application they 
>>>> might want to see if they can reduce the number of 
>>>> java.lang.ref.Reference objects they use.
>>>>
>>>> Hths,
>>>> Bengt
>>>>
>>>>
>>>> On 2014-05-16 10:26, Thomas Viessmann wrote:
>>>>> Hi,
>>>>>
>>>>>
>>>>> I've been tuning a Java 7u51, Solaris 10, T4 system with 24G heap.
>>>>> My customer is not very happy with the remark pauses of up to 2 
>>>>> seconds.
>>>>>  -XX:ParallelGCThreads=48 turned out to be the optimum. Here is 
>>>>> the log file
>>>>> which contains the java args at the top:
>>>>>
>>>>> http://aubing.de.oracle.com/gclog/gc_log_03052014.log
>>>>>
>>>>> Any idea to drive the remark stop times further down?
>>>>>
>>>>>
>>>>> Thanks and Regards
>>>>>
>>>>> Thomas
>>>>
>>>
>>> -- 
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>>> THOMAS VIESSMANN | Senior Principal Technical Support Engineer - Java
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>
> -- 
> Oracle <http://www.oracle.com>
> THOMAS VIESSMANN | Senior Principal Technical Support Engineer - Java
> Phone: +498914302496 <tel:+49814302496> | Mobile: +491743005467 
> <tel:+491743005467>
> Oracle Customer Technical Support - Java
>
> ORACLE Deutschland B.V. & Co. KG | Riesstr.25 | D-80992 Muenchen
>
> ORACLE Deutschland B.V. & Co. KG
> Hauptverwaltung: Riesstr. 25, D-80992 Muenchen
> Registergericht: Amtsgericht Muenchen, HRA 95603
> Geschäftsführere: Juergen Kunz
>
> Komplementärin: ORACLE Deutschland Verwaltung B.V.
> Hertogswetering 163/167, 3543 AS Utrecht, Niederlande
> Handelsregister der Handelskammer Midden-Niederlande, Nr. 30143697
> Geschäftsführer: Alexander van der Ven, Astrid Kepper, Val Maher
>
> ------------------------------------------------------------------------
> ------------------------------------------------------------------------
> Green Oracle <http://www.oracle.com/commitment> Oracle is committed to 
> developing practices and products that help protect the environment

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