Histograms in jVisualVM-VisualGC plugin "not supported"

[John Cuthbertson]

Hi Michael,

You can find some background on the hotspot collectors at: 
https://blogs.oracle.com/jonthecollector/entry/our_collectors

G1 is the latest collector in hotspot and is still evolving. AFAIK the 
monitoring and management tools do work with G1. We would love to hear 
other wise. There may be differences/inconsistencies because the heap in 
G1 is made up of heap regions and the different generations are purely 
logical rather than physical. The the sizes and the regions that make up 
the generations frequently change and G1sometimes returns the, as per 
the spec, invalid or unsupported value for some of the management api 
routines.

Regards,

JohnC

On 10/5/2012 2:28 AM, Michael Finocchiaro wrote:
> Thanks Krystal,
> You are totally right - I needed to explicitly switch using 
> -XX:+UseParNewGC to see the Histograms again.
> Thanks :)
> BTW, does G1 use a similar technique or is there a new parallel 
> algorithm for scavange on new for G1?
> Cheers,
> Fino
>
> Michael Finocchiaro
> michael.finocchiaro at gmail.com <mailto:michael.finocchiaro at gmail.com>
> Mobile Telephone: +33 6 46 59 36 62
> MSN: le_fino at hotmail.com <mailto:le_fino at hotmail.com>
> Twitter: le_fino
> Skype: michael.finocchiaro
> Blog: http://mfinocchiaro.wordpress.com
> LinkedIn: http://fr.linkedin.com/in/mfinocchiaro
>
>
> On Thu, Oct 4, 2012 at 6:56 PM, Krystal Mok <rednaxelafx at gmail.com 
> <mailto:rednaxelafx at gmail.com>> wrote:
>
>     Hi Fino,
>
>     It's possible that you're using a different GC strategy in your
>     Java7 environment from your Java6 one.
>     The VisualGC plugin for VisualVM doesn't support displaying
>     histogram information for ParallelGC; it works with other GCs in
>     HotSpot, e.g. DefNew/ParNew/G1. This hasn't changed from JDK6 to JDK7.
>
>     Please take a look at what GC you're using in the two environments
>     you're comparing.
>
>     - Kris
>
>     On Thu, Oct 4, 2012 at 3:50 AM, Michael Finocchiaro
>     <michael.finocchiaro at gmail.com
>     <mailto:michael.finocchiaro at gmail.com>> wrote:
>
>         Perhaps the wrong forum for this question - if so please
>         redirect me.
>         I upgraded my Java to Java7 but with the same parameters for
>         starting my Tomcat, I am no longer able to see the histograms
>         in the VisualGC plugin to jVisualVM that were so useful for
>         checking the tuning of SurvivorRatio back when I ran on Java6.
>         Is this a known limitation on Java7 or did I miss a
>         command-line parameter somewhere?
>         Cheers,
>         Fino
>
>         Michael Finocchiaro
>         michael.finocchiaro at gmail.com
>         <mailto:michael.finocchiaro at gmail.com>
>         Mobile Telephone: +33 6 46 59 36 62
>         <tel:%2B33%206%2046%2059%2036%2062>
>         MSN: le_fino at hotmail.com <mailto:le_fino at hotmail.com>
>         Twitter: le_fino
>         Skype: michael.finocchiaro
>         Blog: http://mfinocchiaro.wordpress.com
>         LinkedIn: http://fr.linkedin.com/in/mfinocchiaro
>
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