Hi Sylvain,
thank you for sharing all these details!
On Mon, May 5, 2014 at 3:22 PM, Sylvain Goulmy <sygou...@gmail.com> wrote:
> Hi Christopher,
>
> Thank you for your contribution to this thread. I think we we have made
> good progress on the subject, here are some elements i'd like to share :
> - The fact that the response time was increasing with the the number of JSP
> loaded was linked to our monitoring tool... This tool hadn't the same
> impact with websphere. Without monitoring the response time remains stable
> no matter how many jsp are already loaded in the permgen.
Can you disclose what monitoring tool you use and explain how it
impacted the measured value?
> - There is no permgen defined in the IBM JVM running Websphere and i was
> wondering how much space the JVM was allocating to host this huge number of
> JSP. The memory footprint of the process on the system was quite big : Xmx
> : 1,5 Go, memory footprint of the JVM : 3,5 Go. It lets me think that
> Websphere allocates a large space to host these JSP, i increase accordingly
> the permgen size of my JVM to 1Go.
And, did it make a difference?
> - I finally noticed that when the permgen is undersized (ie it cannot host
> all the JSP of my application and has to unload class), the CPU impact is
> much more important with the CMS garbage policy than with the parallel GC.
With "parallel GC" do you mean the default stop the world collector?
> Our main concern so far was the CPU comsumption, we finally solved this by
> tuning our monitoring tool correctly and by increasing the size of the
> permgen.
Did you also try G1 GC? I'd be curios to learn how well that did with
your workload and especially how well it manages to keep GC times
within given limit via -XX:MaxGCPauseMillis.
Kind regards
robert
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