Java Sigar reporting memory usage that disagrees with Windows Resource Monitor

Question

I've downloaded the Java Sigar API (http://support.hyperic.com/display/SIGAR/Home) and would like to use it to get memory usage information about different processes which are running.

I've written the following test case to report memory usage of eclipse.exe:

import org.hyperic.sigar.Sigar;
import org.hyperic.sigar.SigarException;
import org.hyperic.sigar.ptql.ProcessFinder;

public class SigarTest {
    public static void main(String[] args) throws SigarException {
        Sigar sigar = new Sigar();
        ProcessFinder find = new ProcessFinder(sigar);
        long pid = find.findSingleProcess("Exe.Name.ct=eclipse.exe");
        System.out.println(sigar.getProcMem(pid));
    }
}

Executing this code outputs:

{PageFaults=3017940, Size=4125868032, Resident=608493568}

However, looking at the Windows Resource Monitor, it shows the following stats for eclipse.exe:

Commit (KB): 689,356
Working Set (KB): 594,028
Shareable (KB): 47,332
Private (KB): 546,696

See the following screenshot:

The 4.1GB memory usage reported by Sigar isn't even close to any of the memory stats reported by Resource Monitor.

Why are these so far off?

Answer 1

I believe I've found the answer to my own question. Sigar is reporting the Virtual Size (a statistic that is not included in Resource Monitor). An explanation of the difference between Virtual Size and Commit Size can be found here: Windows - Commit Size vs Virtual Size