Startup Time Saving with Restoring Shared Archive

JVM Tutorials - Herong's Tutorial Examples

Dr. Herong Yang, Version 4.10

JVM Tutorials - Herong's Tutorial Examples

∟CDS (Class Data Sharing)

∟Startup Time Saving with Restoring Shared Archive

This section provides a tutorial example on how to save startup time by restoring shared archive 'java -Xshare:on'.

In order to test the saving of start up time with CDS, I wrote the following simple perl program, StartupTimeTest.pl:

#
#- StartupTimeTest.pl
#- Copyright (c) 2004 by Dr. Herong Yang, herongyang.com
#
   ($test) = @ARGV;
   if ($test eq "jdk142") {
      $cmd = "\\j2sdk1.4.2\\bin\\java -cp . Hello";
   } elsif ($test eq "jdk150_off") {
      $cmd = "\\j2sdk1.5.0\\bin\\java -cp . -Xshare:off Hello";
   } elsif ($test eq "jdk150_on") {
      $cmd = "\\j2sdk1.5.0\\bin\\java -cp . -Xshare:on Hello";
   }
   $number = 100;
   $t1 = time();
   for ($i=0; $i<$number; $i++) {
      system($cmd);
   }
   $t2 = time();
   $tt =  $t2 - $t1;
   $at =  $tt/$number;
   print "Command: $cmd\n";
   print "Total time: $tt seconds.\n";
   print "Average time: $at seconds.\n";

Here is how I did my tests:

\j2sdk1.4.2\bin\javac Hello.java
perl StartupTimeTest.pl jdk142
Hello world!
Hello world!
...
Command: \j2sdk1.4.2\bin\java -cp . Hello
Total time: 24 seconds.
Average time: 0.24 seconds.

\j2sdk1.5.0\bin\javac Hello.java
perl StartupTimeTest.pl jdk150_off
Hello world!
Hello world!
...
Command: \j2sdk1.5.0\bin\java -cp . -Xshare:off Hello
Total time: 31 seconds.
Average time: 0.31 seconds.

perl StartupTimeTest.pl jdk150_on
Hello world!
Hello world!
...
Command: \j2sdk1.5.0\bin\java -cp . -Xshare:on Hello
Total time: 18 seconds.
Average time: 0.18 seconds.

The test result is very interest:

With JDK 1.5.0, CDS indeed reduced the startup time of running Hello.java from 0.31 seconds to 0.18 seconds.
However, the startup time of running Hello.java increased from 0.24 seconds to 0.31 seconds between JDK 1.4.2 and JDK 1.5.0.

Last update: 2004.

Table of Contents

About This Book

Download and Install Java SE 1.6 Update 2

java.lang.Runtime Class - The JVM Instance

java.lang.System Class - The Operating System

ClassLoader Class - Class Loaders

Class Class - Class Reflections

Sun's JVM - Java HotSpot VM

JRockit JVM 7.0 by BEA Systems

JRockit JVM 8.0 by BEA Systems

Memory Management Rules and Tests