G1:long remark pauses

Bengt Rutisson bengt.rutisson at oracle.com
Fri May 16 12:32:05 UTC 2014


Hi Thomas,


> 16 maj 2014 kl. 14:01 skrev Thomas Viessmann <thomas.viessmann at oracle.com>:
> 
> Hi Bengt,
> 
> 
> Thanks for confirming. ParallelOld had stop pauses in the range of 20 to 30 seconds.
> CMS was a disaster due to extreme fragmentation and high promotion rate even with
> huge eden and survivors.

Ok, so even with the long remark pauses G1 is performing better than the other GCs?


> There are definitely lots of references. I can find out
> details.

Thanks, it would be interesting to get this data. 

Thanks,
Bengt

> 
> Thanks and Regards
> 
> Thomas 
> 
> 
> 
>> On 05/16/14 13:53, Bengt Rutisson wrote:
>> 
>> 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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>>> Oracle Customer Technical Support - Java
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> -- 
> <oracle_sig_logo.gif>
> THOMAS VIESSMANN | Senior Principal Technical Support Engineer - Java
> Phone: +498914302496 | Mobile: +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
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