Tuning Java virtual machines

The application server, being a Java process, requires a Java virtual machine (JVM) to run, and to support the Java applications running on it. As part of configuring an application server, you can fine-tune settings that enhance system use of the JVM.

About this task

On the z/OS platform there is a JVM in both the controller and servant. This information applies to the JVM in the servant. Usually the JVM in the controller does not need to be tuned.

A JVM provides the runtime execution environment for Java based applications. WebSphere Application Server is a combination of a JVM runtime environment and a Java based server runtime. It can run on JVMs from different JVM providers. To determine the JVM provider on which your Application Server is running, issue the java –fullversion command from within your WebSphere Application Server app_server_root/java/bin directory. You can also check the SystemOut.log from one of your servers. When an application server starts, Websphere Application Server writes information about the JVM, including the JVM provider information, into this log file.

From a JVM tuning perspective, there are two main types of JVMs:
  • IBM JVMs
  • Sun HotSpot based JVMs, including Sun HotSpot JVM on Solaris and HP’s JVM for HP-UX
Even though JVM tuning is dependent on the JVM provider general tuning concepts apply to all JVMs. These general concepts include:
  • Compiler tuning. All JVMs use Just In Time (JIT) compilers to compile Java byte codes into native instructions during server run-time.
  • Java memory or heap tuning. The JVM memory management function, or garbage collection provides one of the biggest opportunities for improving JVM performance.
  • Class loading tuning.

Procedure

What to do next

See Java memory tuning tips for additional tuning information.




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Last updated: Sep 20, 2010 10:03:57 PM CDT
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