does UseParallelOldGC guarantee a better full gc performance

[Jon Masamitsu]

Leon,

I don't think I've actually seen logs with the same flags except changing
parallel old for serial old so hard for me to say.  Simon's  comment

> 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.

says there is a parallel speed up, however, so I'll let you investigate 
you application
and leave it at that.

Jon


On 4/18/2012 9:27 AM, the.6th.month at gmail.com wrote:
> Hi, Jon,
> yup,,,I know, but what is weird is the paroldgen doesn't bring about better
> full gc performance as seen from JMX metrics but bring unexpected swap
> consumption.
> I am gonna look into my application instead for some inspiration.
>
> Leon
>
> On 19 April 2012 00:19, Jon Masamitsu<jon.masamitsu at oracle.com>  wrote:
>
>> **
>> Leon,
>>
>> In this log you see as part of an entry "PSOldGen:" which says you're
>> using the serial mark sweep.  I see in your later posts that "ParOldGen:"
>> appears in your log and that is the parallel mark sweep collector.
>>
>> Jon
>>
>>
>> On 4/18/2012 1:58 AM, the.6th.month at gmail.com wrote:
>>
>> 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>  <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>  <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
>> --http://cometd.orghttp://intalio.comhttp://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
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