What influences young generation pause times?

Y. Srinivas Ramakrishna y.s.ramakrishna at oracle.com
Tue Apr 20 11:00:21 PDT 2010


You could use -XX:+PrintSafepointStatistics etc. to figure these out.

-- ramki

On 04/20/10 10:51, Tony Printezis wrote:
> Matt,
> 
> The pauses that you see seem to be non-GC safepoints. Maybe they are 
> biased lock revocation safepoints. If the log doesn't show a [GC...] 
> line at a safepoint, then there is not GC activity during it (at least I 
> can't think of an occasion when this would be the case).
> 
> Tony
> 
> Matt Khan wrote:
>> Hi Tony
>>
>>   
>>>> Basically, the more objects survive the collection and need to be 
>>>>       
>> copied, the higher the young GC times will be.
>> so when does a concurrent collector enter a STW pause? 
>>
>> for example if I look at figure 6, p10 in the memory management white 
>> paper (http://java.sun.com/products/hotspot/whitepaper.html) then that 
>> makes it look like there is a single STW pause per young collection that 
>> is made shorter because there are n threads doing the work. Is that an 
>> accurate depiction of when it pauses or just a convenient visualisation?
>>
>> My reason for asking is that my app doesn't exhibit this single pause per 
>> young collection, instead I see a succession of short pauses between GC 
>> logs (example below) & I'd like to understand what causes those pauses. 
>> This app is using CMS (params used below) but there is no CMS activity 
>> reported at this time because v little enters the tenured generation and 
>> hence there is no collection required.
>>
>> Total time for which application threads were stopped: 0.0051359 seconds
>> Application time: 99.9576332 seconds
>> 2010-04-13T19:14:53.185+0000: 368542.855: [GC 368542.855: [ParNew
>> Desired survivor size 14450688 bytes, new threshold 1 (max 1)
>> - age   1:    3377144 bytes,    3377144 total
>> : 2986668K->4491K(2998976K), 0.0254753 secs] 3076724K->94963K(3130048K) 
>> icms_dc=0 , 0.0259072 secs] [Time
>> s: user=0.25 sys=0.01, real=0.03 secs] 
>> Total time for which application threads were stopped: 0.0330759 seconds
>> Application time: 190.7387185 seconds
>> Total time for which application threads were stopped: 0.0060798 seconds
>> Application time: 9.2698867 seconds
>> Total time for which application threads were stopped: 0.0051861 seconds
>> Application time: 290.7195886 seconds
>> Total time for which application threads were stopped: 0.0065455 seconds
>> Application time: 9.2792321 seconds
>> Total time for which application threads were stopped: 0.0051541 seconds
>> Application time: 290.7292153 seconds
>> Total time for which application threads were stopped: 0.0063071 seconds
>> Application time: 9.2696694 seconds
>> Total time for which application threads were stopped: 0.0052036 seconds
>> Application time: 290.7093779 seconds
>> Total time for which application threads were stopped: 0.0065365 seconds
>> Application time: 9.2793591 seconds
>> Total time for which application threads were stopped: 0.0051265 seconds
>> Application time: 290.7301471 seconds
>> Total time for which application threads were stopped: 0.0070431 seconds
>> Application time: 9.2694376 seconds
>> Total time for which application threads were stopped: 0.0051428 seconds
>> Application time: 119.4074368 seconds
>> Total time for which application threads were stopped: 0.0059739 seconds
>> Application time: 39.8647697 seconds
>> 2010-04-13T19:40:52.550+0000: 370102.218: [GC 370102.219: [ParNew
>> Desired survivor size 14450688 bytes, new threshold 1 (max 1)
>> - age   1:    2911824 bytes,    2911824 total
>>
>> -Xms3072m 
>> -Xmx3072m 
>> -Xmn2944m 
>> -XX:+DisableExplicitGC 
>> -XX:+PrintGCDetails 
>> -XX:+PrintGCDateStamps 
>> -XX:+PrintGCApplicationStoppedTime
>> -XX:+PrintGCApplicationConcurrentTime
>> -XX:MaxTenuringThreshold=1 
>> -XX:SurvivorRatio=190 
>> -XX:TargetSurvivorRatio=90
>> -XX:+UseConcMarkSweepGC 
>> -XX:+UseParNewGC 
>>
>> Cheers
>> Matt
>>
>> Matt Khan
>> --------------------------------------------------
>> GFFX Auto Trading
>> Deutsche Bank, London
>>
>>
>>
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