[jboss-user] [Performance Tuning] - Re: Physical vs Virtual Memory

[PeterJ]

I think this has to do with how Windows allocates memory. When the JVM first comes up it will as for the 1GB or memory for the heap but it will not immediately make use of that memory. Usually what happens is the OS marks that 1GB of memory as "committed" but physically allocates only a fraction of that to the JVM. As the heap fills up, the OS will allocate more memory to the JVM (that is, swap in memory from the swap file). Of course, the JVM will never really use the full 1GB (probably at most round 3/4GB).

One thing you could try is to allocate, say, 2GB of RAM to a virtual machine and do not allocate any paging file within the OS. That should for at least the Windows running in the VM to not play with the pagefile. If the host OS is also Windows, you can try the same trick there. (That should work - I ran my desktop for a while without any pagefile, didn't even notice it until I tried to run too many VMs are ran out of memory.)

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