does UseParallelOldGC guarantee a better full gc performance

[Simone Bordet]

Hi,

On Wed, Apr 18, 2012 at 13:03, the.6th.month at gmail.com
<the.6th.month at gmail.com> wrote:
> hi, Simon:
> here is another gc-log fragment about full gc, you can see that although
> I've configured the jvm to UseParallelOldGC and increased the younggen size
> to 768m, it still takes 13 seconds to finish the full gc, even worse than
> before.
>
> {Heap before GC invocations=109 (full 2):
>  PSYoungGen      total 705984K, used 14531K [0x00000007d0000000,
> 0x0000000800000000, 0x0000000800000000)
>   eden space 629120K, 0% used
> [0x00000007d0000000,0x00000007d0000000,0x00000007f6660000)
>   from space 76864K, 18% used
> [0x00000007f6660000,0x00000007f7490da8,0x00000007fb170000)
>   to   space 76672K, 0% used
> [0x00000007fb520000,0x00000007fb520000,0x0000000800000000)
>  ParOldGen       total 3309568K, used 3279215K [0x0000000706000000,
> 0x00000007d0000000, 0x00000007d0000000)
>   object space 3309568K, 99% used
> [0x0000000706000000,0x00000007ce25bd68,0x00000007d0000000)
>  PSPermGen       total 262144K, used 79139K [0x00000006f6000000,
> 0x0000000706000000, 0x0000000706000000)
>   object space 262144K, 30% used
> [0x00000006f6000000,0x00000006fad48e38,0x0000000706000000)
> 2012-04-18T18:55:53.500+0800: 767.928: [Full GC [PSYoungGen:
> 14531K->0K(705984K)] [ParOldGen: 3279215K->1474447K(3309568K)]
> 3293746K->1474447K(4015552K) [PSPermGen: 79139K->74190K(262144K)],
> 13.0669910 secs] [Times: user=41.91 sys=0.19, real=13.06 secs]
>
> quite counter-intuitive, huh?

Well, maybe. But it shows that the parallel collector does its work,
since you had a 41.91/13.06 = 3.2x gain on your 4 cores.

The rest of the analysis depends on what your application does (e.g.
allocation rate and whether uses caches, references, etc.) and on a
complete GC log.

Simon
-- 
http://cometd.org
http://intalio.com
http://bordet.blogspot.com
----
Finally, no matter how good the architecture and design are,
to deliver bug-free software with optimal performance and reliability,
the implementation technique must be flawless.   Victoria Livschitz