转：Java Configuration for Blandware AtLeap

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Java Configuration for Blandware AtLeap

To have a stable, robust and fast work of AtLeap you should configure your JVM (Java Virtual Machine) properly. JVM configuration is realized by force of passing parameters. For example for Tomcat you should specify CATALINA_OPTS environment variable, for Resin you should pass it directly into startup script (httpd.exe or httpd.sh), for JBoss you should define JAVA_OPTS environment variable, as for other servlet containers see its documentation.

Let’s examine typical set of JVM arguments

 

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• -server
  

Enable HotSpot Server JIT java compiler. It generates more robust and optimized code, but it slower than HotSpot Client ( -client option) during compilation. See for more information http://java.sun.com/docs/hotspot/index.html http://java.sun.com/products/hotspot/ I recommend use –client for development mode and –server for production mode.

 

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• -Djava.awt.headless=true
  

You need it to have a correct work of graphics parts if the X server is not installed on Linux.

 

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• -Dfile.encoding=UTF-8
  

Specify it to make sure.

 

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• -Xms128m
  

Specify the initial size, in bytes, of the memory allocation pool (128 megabytes in our case).

 

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• -Xmx256m
  

Specify the maximum size, in bytes, of the memory allocation pool (256 megabytes in our case). It should be between ½ and ¾ of physical memory. It is need to avoid problem OutOfMemoryError. You may also be able to avoid this problem by setting the command-line flags -Xmx and -Xms to the same value to prevent the VM from trying to expand the heap. Note that simply increasing the value of -Xmx will not help when no swap space is available.

 

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• -XX:PermSize=64m
  

Specify the initial size of the permanent generation (where the VM stores the classes and methods data).

 

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• -XX:MaxPermSize=128m
  

Specify the max size of the permanent generation (where the VM stores the classes and methods data). If case of the -server option is enabled the default value equal to 64m but in case of java.lang.OutOfMemoryError: PermGen space error you should increase this value. This option does not exist in Bea JRockit and IBM JVMs.

 

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• -XX:NewSize=16m
  

Specify the initial size of the young generation (where the VM stores the short-lived objects).

 

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• -XX:MaxNewSize=24m
  

Specify the maximum size of the young generation (where the VM stores the short-lived objects).

Please carefully read Java documentation for your platform. For example for Solaris it is recommended to specify -XX:-UseLWPSynchronization option.

If your machine has more than two CPU the following options can be useful: -XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:+CMSParallelRemarkEnabled They allow to enable Concurrent Low Pause Collector.

If your machine has more than two CPU and your Sun JDK 1.5.0_06 or more you can try to use -XX:+UseParallelGC -XX:+UseParallelOldGC -XX:+UseAdaptiveSizePolicy in order to enable throughput collector.

if you have a IPv6 OS core but need to work with IPv4 addresses specify -Djava.net.preferIPv4Stack=true

If you startup Tomcat under Windows as service you should specify JVM options via Windows registry HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ApacheTomcat\Parameters (add JVM Option Number N string value and increase JVM Option Count).

As result for Linux we can get following line CATALINA_OPTS="-server -Djava.awt.headless=true -Dfile.encoding=UTF-8 -Xms128m -Xmx256m -XX:PermSize=64m -XX:MaxPermSize=128m -XX:NewSize=16m -XX:MaxNewSize=24m"

As for options for Ant you can use e.g. the following line: ANT_OPTS="-Djava.awt.headless=true -Dfile.encoding=UTF-8 -Xms64m -Xmx128m"

Be careful, non-standard JVM options (which begins from -XX:) can be applied only for Sun's JVM. In order to make tuning of IBM or Bea's JVMs please read documentation.

Below links can be useful during JVM tuning:

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• http://java.sun.com/docs/performance/
  
• http://www.tagtraum.com/gcviewer.html