Java process on windows using less memory than specified by -xms?

Question

I start my server using the command "java -xms 1280m -xmx 1280m". On Linux machines, this works fine, and I see that the process uses almost the same amount of memory. However, on Windows machines, I see that the java process uses significantly less than 1280 m - about 500-600 m. I collected this data from the Windows task manager, if that matters. Both Windows machines that I checked are Windows 2003 servers and have 2 GB and 3 GB of RAM, respectively. I always thought that specifying the initial heap size on -xms would force java to use at least most of the memory. Am I mistaken? Or is it a feature with java on Windows?

Answer 1

Windows Task Manager was designed for end users, not programmers. The latter usually prefer Process Explorer ( procexp.exe) from the Sysinternals package. This combined with vmmap.exewill show you exactly what is happening.

Answer 2

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Answer 3

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Windows XP java -xms Unrecognised option

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So it seems that my comment is valid and you need to sort the shell by your command.

Answer 4

In addition to what Kevin D said about capitalization, note that 32-bit Windows systems typically have an upper bound on the maximum heap size. It tends to change depending on many factors, but I often saw this right around 1280 m that you are trying. I doubt there is a problem here, but it could be a related problem.