Re: Should -Xmx be a multiple of -Xms?
On 01-06-2010 14:06, Tom Anderson wrote:
A colleague mentioned that he'd heard (from this guy's cousin's
mechanic's guy who he met in a bar's grandfather's dealer's sysop) that
the JVM requests memory from the OS in chunks of the size of -Xms, and
that you should therefore always set -Xmx to be a whole multiple of
-Xms, otherwise it would never actually request its way up to it
(because you can't make a litre from any whole number of fluid ounces).
I think i'd heard something similar at some point, although from a less
reliable source.
Is there any truth to this? Was there ever?
No truth with SUN Java 1.6.
I very much doubt there was any truth with other implementations. But
one never knows.
To very try run this with various Xms and Xmx:
import java.util.ArrayList;
import java.util.List;
public class MemIncr {
public static void main(String[] args) {
Runtime rt = Runtime.getRuntime();
List<byte[]> lst = new ArrayList<byte[]>();
while(true) {
System.out.println((rt.totalMemory() - rt.freeMemory()) + "
out of " + rt.totalMemory() + " used (max is " + rt.maxMemory() + ")");
lst.add(new byte[1000000]);
}
}
}
Arne
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