gc log analysis tools

Jon Masamitsu Jon.Masamitsu at Sun.COM
Fri Oct 26 07:54:37 UTC 2007


It's typical to see lower performance with the 64bit VM.  A drop of 23%
seems a little high
but is in the ball park.  The drop in performance comes from the
increased memory traffic
due to the larger objects.  

Hope that helps.


PS.  I don't think the output from -verbosegc changed at all between jdk
1.4.2 and jdk 5.
If it did, I think the change was very minor.  One difference you might
see with jdk 5 is that
you could be getting a different default garbage collector.   That might
be the source of
differences in the logs you're trying to analyze.

Ben Cheng wrote:

> The reason I am interested in this information is because I have a
> benchmark whose score is X using 32-bit VM and 2G of heap. When I
> switched to 64-bit build of the same VM, the score dropped to 0.77X
> with the same amount of heap. If I increase the heap size to 3.5G (on
> a machine with 4GB of RAM), the score went to to 1.40X.
> What I need is pretty basic - it sums up all the gc time from the
> verbose log during a benchmark run, as I want to verify if the change
> in gc time correlates to the change in performance. I can write a
> similar script to do that, but I just want to check to see if there is
> a working tool out there already. Apparently the verbose gc log format
> changed from 1.5 and beyond and the old script is not compatible.
> Thanks,
> -Ben
> On 10/25/07, * Neo Jia* <neojia at gmail.com <mailto:neojia at gmail.com>>
> wrote:
>     Ben,
>     What is your opion? I had one but not sure if it would work for
>     you or not (
>     I have not worked on JDK for a while ...
>     Thanks,
>     Neo
>     On 10/25/07, Ben Cheng < bccheng at google.com
>     <mailto:bccheng at google.com>> wrote:
>     > Hi,
>     >
>     > I was trying to get a sense of total GC time spent in a Java app
>     using 1.6
>     > JDK. The gc logs (w/ and wo/ parallel gc) seem to break the
>     ancient tool
>     > gc_analyze.pl found on the web.
>     >
>     > Is there an update to date tool to produce the desired
>     information for new
>     > JDKs?
>     >
>     > Thanks in advance,
>     > -Ben
>     >
>     --
>     I would remember that if researchers were not ambitious
>     probably today we haven't the technology we are using!

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