does UseParallelOldGC guarantee a better full gc performance

[the.6th.month at gmail.com]

Hi, Simon:

this is the full gc log for your concern.
2012-04-18T16:47:24.824+0800: 988.392: [GC
Desired survivor size 14876672 bytes, new threshold 1 (max 15)
 [PSYoungGen: 236288K->8126K(247616K)] 4054802K->3830711K(4081472K),
0.0512250 secs] [Times: user=0.15 sys=0.00, real=0.05 secs]

2012-04-18T16:47:24.875+0800: 988.443: [Full GC [PSYoungGen:
8126K->0K(247616K)] [PSOldGen: 3822585K->1751429K(3833856K)]
3830711K->1751429K(4081472K) [PSPermGen: 81721K->81721K(262144K)],
6.6108630 secs] [Times: user=6.62 sys=0.00, real=6.61 secs]

the full gc time is almost unchanged since I enabled paralleloldgc.

Do you have any recommendation for an appropriate young gen size?

Thanks

All the best,
Leon


On 18 April 2012 16:24, Simone Bordet <sbordet at intalio.com> wrote:

> Hi,
>
> On Wed, Apr 18, 2012 at 10:16, the.6th.month at gmail.com
> <the.6th.month at gmail.com> wrote:
> > hi all:
> > I'm currently using jdk 6u26. I just enabled UseParallelOldGC, expecting
> > that would enhance the full gc efficiency and decrease the mark-sweep
> time
> > by using multiple-core. The JAVA_OPTS is as below:
> > -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintTenuringDistribution
> > -Xloggc:gc.log-server -Xms4000m -Xmx4000m -Xss256k -Xmn256m
> > -XX:PermSize=256m -XX:+UseParallelOldGC  -server
> > -Dorg.apache.jasper.compiler.Parser.STRICT_QUOTE_ESCAPING=false
> > as shown in jinfo output, the settings have taken effect, and the
> > ParallelGCThreads is 4 since the jvm is running on a four-core server.
> > But what's strange is that the mark-sweep time remains almost unchanged
> (at
> > around 6-8 seconds), do I miss something here? Does anyone have the same
> > experience or any idea about the reason behind?
> > Thanks very much for help
>
> The young generation is fairly small for a 4GiB heap.
>
> Can we see the lines you mention from the logs ?
>
> Simon
> --
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