How to read the output of +PrintTenuringDistribution

[Srinivas Ramakrishna]

Hi Ji --

Are you using ParNew by itself without CMS in the old gen, or are you using
CMS in the old gen.
If the former, I have a possible explanation (although you will need to
evaluate the statistical probability
of an event based on the configuration and object demographics to determine
if it's plausible in your
case).

If, however, you are using CMS in the old gen, then I don't have an
explanation.

So, what is your config? :-)

-- ramki



On Thu, Oct 24, 2013 at 11:40 PM, Tao Mao <tao.mao at oracle.com> wrote:

>  Hi Ji,
>
> From what you've reported, it definitely looks weird. Are these two GC's
> consecutive two GC's (i.e. no other GC/s in between)?
>
> Thanks.
> Tao
>
>
> On 10/24/13 9:45 PM, Ji Cheng wrote:
>
> Hello,
>
>  I have gc log enabled with -XX:+PrintTenuringDistribution. But I'm quite
> confused with the tenuring distribution below.
>
>  =============
>  2013-10-19T19:46:30.244+0800: 169797.045:
> [GC2013-10-19T19:46:30.244+0800: 169797.045: [ParNew
> Desired survivor size 87359488 bytes, new threshold 4 (max 4)
> - age   1:   10532656 bytes,   10532656 total
> - age   2:   14082976 bytes,   24615632 total
> - age   3:   15155296 bytes,   39770928 total
> - age   4:   13938272 bytes,   53709200 total
> : 758515K->76697K(853376K), 0.0748620 secs] 4693076K->4021899K(6120832K),
> 0.0756370 secs] [Times: user=0.42 sys=0.00, real=0.07 secs]
> 2013-10-19T19:47:10.909+0800: 169837.710: [GC2013-10-19T19:47:10.909+0800:
> 169837.711: [ParNew
> Desired survivor size 87359488 bytes, new threshold 4 (max 4)
> - age   1:    9167144 bytes,    9167144 total
> - age   2:    9178824 bytes,   18345968 total
> - age   3:   16101552 bytes,   34447520 total
> - age   4:   21369776 bytes,   55817296 total
> : 759449K->63442K(853376K), 0.0776450 secs] 4704651K->4020310K(6120832K),
> 0.0783500 secs] [Times: user=0.43 sys=0.00, real=0.07 secs]
>  =============
>
>  From What I read, there are 10532656 bytes in age 1 (survived from 1 GC)
> in the first gc. In the second gc, 9178824 bytes in age 2 (survived from 2
> GCs). This is fine since some objects died between the first and second GC.
>
>  But in the second GC, 16101552 bytes are in age 3 while only 14082976
> bytes in age 2 in the first GC. I don't why this number is increasing.
> Shouldn't all bytes in age n come from age n-1 in the previous GC? Or I
> misinterpreted those numbers?
>
>  btw, the jvm version is 1.7.0_40.
>
>  Thanks.
>
>  Ji Cheng
>
>
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