Intel 7xx Servers, 170 Servers, AS/400 RISC Server manual WebSphere Application Server

WebSphere Application Server V6.1

Historically, new releases of WebSphere Application Server have offered improved performance and functionality over prior releases of WebSphere. WebSphere Application Server V6.1 is no exception. Furthermore, the availability of WebSphere Application Server V6.1 offers an entirely new opportunity for WebSphere customers. Applications running on V6.1 can now operate with either the “Classic”

64-bit Virtual Machine (VM) or the recently released IBM Technology for Java, a 32-bit VM that is built on technology being introduced across all the IBM Systems platforms.

Customers running releases of WebSphere Application prior to V6.1 will likely be familiar with the Classic 64-bit VM. This continues to be the default VM on i5/OS, offering competitive performance and excellent vertical scalability. Experiments conducted using the Trade6 benchmark show that WebSphere Application Server V6.1 running on the Classic VM realized performance gains of 5-10% better throughput when compared to WebSphere Application Server V6.0 on identical hardware.

In addition to the presence of the Classic 64-bit VM, WebSphere Application Server V6.1 can also take advantage of IBM Technology for Java, a 32-bit implementation of Java supported on Java 5.0 (JDK 1.5). For V6.1 users, IBM Technology for Java has two key potentially beneficial characteristics:

ySignificant performance improvements for many applications - Most applications will see at least equivalent performance when comparing WebSphere Application Server on the Classic VM to IBM Technology for Java, with many applications seeing improvements of up to 20%.

y32-bit addressing allows for a potentially considerable reduction in memory footprint - Object references require only 4 bytes of memory as opposed to the 8 bytes required in the 64-bit Classic VM. For users running on small systems with relatively low memory demands this could offer a substantially smaller memory footprint. Performance tests have shown approximately 40% smaller Java Heap sizes when using IBM Technology for Java when compared to the Classic VM.

It is important to realize that both the Classic VM and IBM Technology for Java have excellent benefits for different applications. Therefore, choosing which VM to use is an extremely important consideration. Chapter 7 - Java Performance has an extensive overview of many of the key decisions that go into choosing which VM to use for a given application. Most of the points in Chapter 7 are very much important to WebSphere Application Server users. One issue that will likely not be a concern to WebSphere Application Server users is the additional overhead to native ILE calls that is seen in IBM Technology for Java. However, if native calls are relevant to a particular application, that consideration will of course be important. While choosing the appropriate VM is important, WebSphere Application Server V6.1 allows users to toggle between the Classic VM and IBM Technology for Java either for the entire WebSphere installation or for individual application server profiles.

While 32-bit addressing can provide smaller memory footprints for some applications, it is imperative to understand the other end of the spectrum: applications requiring large Java heaps may not be able to fit in the space available to a 32-bit implementation of Java. The 32-bit VM has a maximum heap size of 3328 MB for Java applications. However, WebSphere Application Server V6.1 using IBM Technology for Java has a practical maximum heap size of around 2500 MB due in part to WebSphere related memory demands like shared classes. The Classic VM should be used for applications that require a heap larger than 2500 MB (see Chapter 7 - Java Performance for further details).

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