Class Data Sharing

Question

I am trying to benchmark memory footprint using the class data sharing feature on Solaris8 and Solaris9.
I wrote a small sample java program MyApp.java as follows,
     import java.lang.*;
     public class MyApp {
          public static void main(String[] args) {
               System.out.println("Java VM Version Number = " + System.getProperty("java.vm.version"));
               long maxMem = Runtime.getRuntime().totalMemory();
               System.out.println("Total Memory in bytes= " + maxMem);
               long freeMem = Runtime.getRuntime().freeMemory();
               System.out.println("Free Memory in bytes= " + freeMem);
               long memUsed = maxMem - freeMem;
               System.out.println("Memory Used in bytes= " + memUsed);
               long t1 = System.currentTimeMillis();
               for (int i = 0; i < 3; i++)
                    try
                         System.out.println("iteration count = " + i+1);
                         Thread.sleep(1000 * 60);
                         long t2 = System.currentTimeMillis();
                         long t3 = t2 - t1;
                         System.out.println("time elapsed in milliseconds = " + t3);
                    catch (InterruptedException e)
     $JAVA_HOME = /packages/sun/j2sdk1.5.0_02/jdk1.5.0_02/
     I ran it both the machines with the following options
     1)     $JAVA_HOME/bin/java �client �Xshare:on MyApp
     2)     $JAVA_HOME/bin/java �client �Xshare:off MyApp
     I ran the pmap command with �x option to get the readings
     A) Solari8:
          VM Option     RSS          Shared Mem          Private Mem
          Xshare:on     53584KB     50600KB          2984KB
          XShare:off     11456KB     7808KB          3648KB
          JDK1.4     29736KB     26392KB          3344KB
     B) Solaris9:
          VM Option      RSS          Anonymous mem
          Xshare:on     49384KB     3048KB
          Xshare:off     48576KB     3704KB
          JDK1.4     33656KB     2856KB
     These numbers repeat for multiple instances of the same application.
     I do not see the expected memory savings.
     I am trying to find out if I am missing any step in the process of using
     Class Data Sharing feature of JDK1.5
Thanks!!

Answer 1

Samantha10 wrote:
Is this class data sharing possible for user defined classes also? i have a singleton class which i am invoking through a script. The script has been scheduled to run every 1 sec . Since it is being invoked every 1 sec hence the singleton pattern is failing . Hence if the this class data sharing is possible then the singleton pattern can be made applicable.If you have a single process and you have a single class loaded by two different ClassLoader instances
in some respects they will be two different classes
if (class1 instanceof class2.getClass())returns false.
This is not the case for Java core classes because they are always loaded by the SystemClassLoader.
You write you
have a singleton class which i am invoking through a script. What approach to you use to invoke the singleton?
I am trying to figure out if you launch a new JVM every second...
Maybe you can use Nailgun.