WebLogic: The Definitive Guide

Tuning the JVM

Clearly, the JVM’s performance also affects WebLogic’s performance. Most aspects of JVM tuning relate to the efficient management of the memory heap, an efficient garbage collection scheme, and the choice between two Unix threading models: green and native threads.

Choosing a JVM

WebLogic publishes a list of certified JVM and operating system combinations on its web site; we recommend that you only use one of these certified combinations. This list also indicates what JVM version can be used. For example, WebLogic 8.1 supports JDK 1.4.1, whereas WebLogic 7.0 supports JDK 1.3.1.

SunSoft’s JVM and BEA’s JRockit are the two most commonly used JVMs. JRockit is a production VM optimized for server-side applications on Intel platforms. WebLogic 8.1 installs with a version of JRockit 8. You can download a version of JRockit 7 for WebLogic 7.0 from BEA’s dev2dev web site.

The right JVM will strike a balance between several constraints, such as operating system, hardware and JVM stability, and performance. You can reference third-party documents for an overview of the general performance characteristics of the various JVMs.

Heap Size and Garbage Collection

The Java heap represents the memory space for all runtime objects. At any time, the heap consists of live objects, dead objects, and free memory. When an object is no longer referenced by anyone, it is considered “garbage” and is ready to be reclaimed as free memory. Garbage collection is the JVM’s way of managing the JVM ...