How does JVM decide the tenuringThreshold?

Wed Dec 16 23:54:07 UTC 2015

Jun,

First note that you are using the UseParallelGC collector and it
changes the tenuring threshold and survivor space sizes
differently than the other collectors.  You might find this helpful.

https://blogs.oracle.com/jonthecollector/entry/the_unspoken_the_why_of

In particular turn on -XX:AdaptiveSizePolicyOutputInterval=1 and it
will output reasons why heap sizes and tenuring threshold are being
changed.

On 12/16/2015 01:52 PM, Jun Zhuang wrote:
>
> Hi,
>
> I am trying to gain some knowledge regarding how GC works by running 
> load tests against a java web service, hosted on JBOSS, and adjusting 
> various java startup parameters. One interesting thing I noticed was 
> the tenuring threshold, I thought it would change with size of the 
> survivor space, but I could never make it happen, can someone provide 
> some clue? Following is what I did:
>
> *_JAVA startup parameters:_*
>
> -Xms2g -Xmx2g -XX:MaxPermSize=256m -XX:NewSize=128m 
> -XX:MaxNewSize=128m -XX:SurvivorRatio=126
>
> I then changed the SurvivorRatio to 30, 6, and 1, but the “new 
> threshold” in the GC log always stayed at 1 after the first few young 
> GCs, adding -XX:TargetSurvivorRatio=90 did not seem to make any 
> difference:
>

Use InitialTenuringThreshold to affect the starting threshold.

> 4.504: [GC
>
> Desired survivor size 16777216 bytes, new threshold 7 (max 15)
>
>  [PSYoungGen: 98304K->7553K(114688K)] 98304K->7553K(2080768K), 
> 0.0199500 secs] [Times: user=0.04 sys=0.01, real=0.02 secs]
>
> 12.784: [GC
>
> Desired survivor size 16777216 bytes, new threshold 7 (max 15)
>
>  [PSYoungGen: 105857K->8979K(114688K)] 105857K->8979K(2080768K), 
> 0.0177280 secs] [Times: user=0.04 sys=0.01, real=0.01 secs]
>
> 18.935: [GC
>
> Desired survivor size 16777216 bytes, new threshold 7 (max 15)
>
>  [PSYoungGen: 107283K->13322K(114688K)] 107283K->13322K(2080768K), 
> 0.0282660 secs] [Times: user=0.06 sys=0.00, real=0.02 secs]
>
> 22.944: [GC
>
> Desired survivor size 16777216 bytes, new threshold 7 (max 15)
>
>  [PSYoungGen: 111626K->11304K(114688K)] 111626K->11377K(2080768K), 
> 0.0255770 secs] [Times: user=0.08 sys=0.00, real=0.03 secs]
>
> 24.089: [GC
>
> Desired survivor size 16777216 bytes, new threshold 6 (max 15)
>
>  [PSYoungGen: 109608K->16377K(114688K)] 109681K->17678K(2080768K), 
> 0.0373650 secs] [Times: user=0.10 sys=0.01, real=0.04 secs]
>
> 24.801: [GC
>
> Desired survivor size 16777216 bytes, new threshold 5 (max 15)
>
>  [PSYoungGen: 114681K->16358K(114688K)] 115982K->21621K(2080768K), 
> 0.0627800 secs] [Times: user=0.21 sys=0.01, real=0.06 secs]
>
> 25.500: [GC
>
> Desired survivor size 16777216 bytes, new threshold 4 (max 15)
>
>  [PSYoungGen: 114662K->16359K(114688K)] 119925K->30181K(2080768K), 
> 0.0577540 secs] [Times: user=0.17 sys=0.01, real=0.06 secs]
>
> 26.280: [GC
>
> Desired survivor size 16777216 bytes, new threshold 3 (max 15)
>
>  [PSYoungGen: 114663K->16354K(114688K)] 128485K->37506K(2080768K), 
> 0.0539360 secs] [Times: user=0.15 sys=0.01, real=0.05 secs]
>
> 27.330: [GC
>
> Desired survivor size 16777216 bytes, new threshold 2 (max 15)
>
>  [PSYoungGen: 114658K->14928K(114688K)] 135810K->42581K(2080768K), 
> 0.0588730 secs] [Times: user=0.20 sys=0.01, real=0.06 secs]
>
> 28.108: [GC
>
> Desired survivor size 16777216 bytes, new threshold 1 (max 15)
>
>  [PSYoungGen: 113232K->16363K(114688K)] 140972K->59269K(2080768K), 
> 0.0586460 secs] [Times: user=0.15 sys=0.01, real=0.06 secs]
>
> . . .
>
> 1538.726: [GC
>
> Desired survivor size 3932160 bytes, new threshold 1 (max 15)
>
>  [PSYoungGen: 129280K->1792K(125184K)] 433305K->308417K(2091264K), 
> 0.2403020 secs] [Times: user=0.83 sys=0.01, real=0.24 secs]
>
> 1543.537: [GC
>
> Desired survivor size 4063232 bytes, new threshold 1 (max 15)
>
>  [PSYoungGen: 125184K->2592K(126016K)] 431809K->310233K(2092096K), 
> 0.2318620 secs] [Times: user=0.83 sys=0.01, real=0.23 secs]
>
> 1548.268: [GC
>
> Desired survivor size 3932160 bytes, new threshold 1 (max 15)
>
>  [PSYoungGen: 125984K->1344K(127232K)] 433625K->310657K(2093312K), 
> 0.2294920 secs] [Times: user=0.83 sys=0.01, real=0.23 secs]
>
> If the threshold is really 1, then nothing should be promoted to the 
> old gen, but that definitely was not the case.
>

Threshold of 1 will promote everything.

> -------------------------------------------------------------------------------------------------------
>
> I also experimented with -XX:-UsePSAdaptiveSurvivorSizePolicy, the 
> “new threshold” always stays at 7 despite the SurvivorRatio value.
>

Yes, turning off UsePSAdaptiveSurvivorSizePolicy stops the adjustment of 
the tenuring threshold and survivor spaces
for UseParallelGC.

Jon
>
> 1643.408: [GC
>
> Desired survivor size 4194304 bytes, new threshold 7 (max 15)
>
>  [PSYoungGen: 519729K->4032K(520192K)] 935797K->420443K(2093056K), 
> 0.2605620 secs] [Times: user=0.94 sys=0.01, real=0.26 secs]
>
> 1662.092: [GC
>
> Desired survivor size 4194304 bytes, new threshold 7 (max 15)
>
>  [PSYoungGen: 520128K->4096K(520192K)] 936539K->421235K(2093056K), 
> 0.2588890 secs] [Times: user=0.95 sys=0.01, real=0.26 secs]
>
> 1680.882: [GC
>
> Desired survivor size 4194304 bytes, new threshold 7 (max 15)
>
>  [PSYoungGen: 520192K->4096K(520192K)] 937331K->422347K(2093056K), 
> 0.2661180 secs] [Times: user=0.97 sys=0.00, real=0.27 secs]
>
> 1698.975: [GC
>
> Desired survivor size 4194304 bytes, new threshold 7 (max 15)
>
>  [PSYoungGen: 520192K->4096K(520192K)] 938443K->423246K(2093056K), 
> 0.2626090 secs] [Times: user=0.95 sys=0.01, real=0.26 secs]
>
> Appreciate any input,
>
> Jun
>
> *//*
>
> */Jun Zhuang/**//*
>
> /Sr. Performance QA Engineer | Hobsons///
>
>
>
> _______________________________________________
> hotspot-gc-use mailing list
> hotspot-gc-use at openjdk.java.net
> http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.openjdk.java.net/pipermail/hotspot-gc-use/attachments/20151216/014753c4/attachment.html>