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From "Leon Rosenberg" <>
Subject Re: CPU usage quirk with multiple tomcat instances
Date Tue, 06 May 2008 08:33:09 GMT
Hello Dan,

what also may happening is that you have unneeded or errorneous
synchronisation somewhere in your code. Two instances : less code in
same block and vm, effectively less synchronization.

try to profile whether some use cases take longer on the single tomcat
per machine.

We once tried to run multiple tomcats on one machine and the results
where opposed to yours: less performance, so i think your app behaves
"funny" :-)


On Fri, May 2, 2008 at 2:42 PM, Lists <> wrote:
> Hi,
>  We have a Tomcat app that is loadbalanced by hardware.  I have 4 boxes
>  available in our test env, all of which vary slightly but not massively in
>  spec.
>  Anyway I moved from 2 tomcat instances on each machine ( listening on
>  different ports ) down to 1 and I noticed for the same load the cpu
>  utilisation dropped by 20%.  Interesting, how can this be explained?  Is
>  this the extra effort in tomcat or something?  Or is it memory related? the
>  2 instances had 1gb each, and the single one has been given 4gb.  However I
>  have jprofiled the instance and it has never seemed memory hungry.  Anyway I
>  suspect even at 2gb for 1 instance it would still be 20% less cpu - i can
>  always do a run to prove this if people think that necessary..
>  Another thing i've found is that on one server I have abnormally high CPU
>  utilisation for the same load.  I've checked the logging levels are all the
>  same as are the java VM and the VM config settings.  I wonder what else
>  could cause this?  All i can think is some sort of OS or hardware
>  malfunction! maybe the CPU cache is duff or something.
>  Many thanks to any input to my Friday weird-ness!
>  Dan
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