There are several configuration settings you can change to improve
Java virtual machine (JVM) performance on the z/OS platform.
Before you begin:
- Ensure that the most recent version of JVM that WebSphere Application
Server supports for the z/OS platform is installed on your system.
- Have the most recent WebSphere Application Server service for the z/OS
platform installed on your system. Almost every PTF level includes improved
JVM performance.
- Have sufficient JVM Heap Size.
How to view or set:
- In the WebSphere Application Server administrative
console, click Servers > Application Servers > server_name
> Process Definition > Control > Java Virtual Machine.
- Select the options that are listed on the Configuration tab.
- Run with the JIT (Just In Time) compiler active.
In the General Properties
section of the Configuration Tab, ensure that Disable JIT is not selected.
The default is JIT support enabled.
- Do not specify the debug version of the JVM libjava_g
in your libpath. Severe performance degradation is likely when running with
the debug version of the JVM.
- Have Classpath point to only the classes you need (the classes that are
referenced most frequently should be located near the front of the path, if
possible).
In the General Properties section of the Configuration Tab,
enter the Classpath in the text box of the Classpath option.
- Verify the Classpath as part of the Java configuration.
- To speed up JVM initialization and improve server startup time, specify
the following command line arguments in the General JVM Arguments field in
the General Properties section of the Configuration Tab.
-Xquickstart
-Xverify:none
For JDK Version 1.4.1 the specification reduces servant startup time
at the cost of some runtime performance. For JDK Version 1.3.1, these options
can reduce servant startup time by as much as 40%. However, they will reduce
runtime throughput by about 8%.
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