What influences young generation pause times?

Tony Printezis tony.printezis at oracle.com
Tue Apr 20 10:51:58 PDT 2010


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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