Intel 7xx Servers, 170 Servers manual Java Performance, Introduction, What’s new in V6R1

Chapter 7. Java Performance

Highlights:

yIntroduction

yWhat’s new in V6R1

yIBM Technology for Java (32-bit and 64-bit)

yClassic VM (64-bit)

yDetermining Which JVM to Use

yCapacity Planning

yTips and Techniques

yResources

7.1 Introduction

Beginning in V5R4, IBM began a transition to a new VM implementation for i5/OS, IBM Technology for Java, to replace the Classic VM. This transition continues in V6R1 with the introduction of a 64-bit version of IBM Technology for Java, providing a new solution for Java applications which require large amounts of memory. The transition is expected to be completed in the next version of i5/OS, which will no longer support the Classic VM. In the mean time, one of the key performance -related decisions for i5/OS Java users is which JVM to use.

Earlier versions of this document have followed the performance of Java from its infancy to maturity. Early Java applications were often a departure from the traditional OS/400 application architecture, with custom application code responsible for a large portion of the CPU used by the application. Therefore, earlier versions of this document emphasized micro-optimizations – relatively small (though often pervasive) changes to application code to improve performance.

Today’s Java applications, however, typically rely on a variety of system services such as JDBC, encryption, and security provided by i5/OS, the Java Virtual Machine (VM), and WebSphere Application Server (WAS), along with other products built on top of WebSphere. As a result, many Java applications now spend far more time in these system services than in custom code. For many applications, this means that performance depends mainly on the performance of IBM code (i5/OS, the Java VM, WebSphere, etc.) and the way that these services are used by the application. Micro-optimizations can still be important in some cases, but are not as critical as they have been in the past.

Tuning is also important for getting good performance in the Java environment. Tuning garbage collection is perhaps the most common example. Thread and connection pool tuning is also frequently important. Proper tuning of i5/OS can also make a big impact on Java application performance.

7.2 What’s new in V6R1

In V5R4 IBM introduced IBM Technology for Java, a new VM implementation built on technology used across all of the IBM Systems platforms. In V5R4 only a 32-bit version of IBM Technology for Java was supported; in V6R1, a new 64-bit version of IBM Technology for Java is also available, providing a new

IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
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