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
My guess (and that's all it is) is that you have eliminated much of the
context-switching overhead that two instances would have compared to one.
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.
What is this cpu (type and speed) compared to the others? If it's a
slower or less-capable (no numeric coprocessor, etc) cpu, the same load
would be a high percentage of its capability.
Many thanks to any input to my Friday weird-ness!
Dan
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