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maximum heap size setting and cpu utilization

843829Jun 4 2010 — edited Jun 4 2010
On an application running in Windows server 2008 environment with two quad core processors and 16GB of RAM

I ran a multi-threaded process with maximum heap size set to --xMx12000M which was returning a CPU utilization of 12% which was too low although the process was running ok. When increased this setting by 1000M , the CPU utilization went up to 100% which would be the intended figure for this application. Can setting the heap size too low cause this sort of CPU under utilization without throwing an OutOfMemory exception? From an operating system perspective neither run was causing any visible memory issues..

Comments

843829
nry2006 wrote:
On an application running in Windows server 2008 environment with two quad core processors and 16GB of RAM

I ran a multi-threaded process with maximum heap size set to --xMx12000M which was returning a CPU utilization of 12% which was too low although the process was running ok. When increased this setting by 1000M , the CPU utilization went up to 100% which would be the intended figure for this application.
Don't attempt to measure your applications performance by CPU utilization.

Measure how much work (whatever it is doing) it does at different heap settings.
843829
In this case the performance (in terms of time to process) is directly related to CPU utilization. I expect CPU utilization to be maximized as the threads are mainly computationally bound.otherwise the process time to run dramatically increases.
843829
nry2006 wrote:
In this case the performance (in terms of time to process) is directly related to CPU utilization. I expect CPU utilization to be maximized as the threads are mainly computationally bound.otherwise the process time to run dramatically increases.
From CPU utilization at 100% all you know is a lot of CPU is being consumed by something (some thread or several threads).
How would you know it is not the JVM doing background stuff (like GC).
843829
In this case the performance (in terms of time to process) is directly related to CPU utilization. I expect CPU utilization to be maximized as the threads are mainly computationally bound.otherwise the process time to run dramatically increases.
843829
From CPU utilization at 100% all you know is a lot of CPU is being consumed by something (some thread or several threads).
How would you know it is not the JVM doing background stuff (like GC).
843829
I know as each thread has a numerical task to perform which does not require it creating or destroying any object instances - so I don't believe gc is an issue, although I expect memory management is an issue depending on whether you provide sufficient heap space - hence my original query.
843829
try to verify garbage collector log, because the only diffrence between having the problem and not is the increase of the heap. So garbage collector has to work harder.

give us the content of GC log when the problem occur.
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Locked on Jul 2 2010
Added on Jun 4 2010
#java-virtual-machine-jvm
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