Chapter 5. Performance tuning 109
Model 270 feature 2252 Processor CPW 950 Interactive CPW 0
Model 820 feature 2396 Processor CPW 950 Interactive CPW 35
Notice the considerable variation in the processor CPW and the low interactive CPW. The
variation in processor CPW may be because, although CPW is a good indicator of RPG and
Cobol performance, it is not a good indicator of Java and WebSphere performance. Java
performance is significantly affected by processor features, such as L2 cache, which do not
affect the CPW rating as much.
There is a low interactive CPW is because WebSphere does not need interactive CPW. Little
dumb terminal work is required to manage a WebSphere application. The small amount that
is needed, such as starting the QEJBSBS subsystem, may be performed from the console.
Because of the single task exemption, this is possible even on a system with an interactive
CPW of 0. Of course, a call.connect or vendor.connect user may be running System21 on the
same system. This requires a certain amount of interactive CPW, but the WebSphere
applications do not add to this requirement.
In V5R1, IBM introduced a new benchmark called
Compute Intensive Workload (CIW). This is
calculated differently than CPW. It depends more on such factors as the processor speed and
depends less on system services. It is hoped that this value will be a better indicator of the
likely performance of Java- and WebSphere-based applications. Unfortunately, IBM has only
published CIW figures for the new V5R1 models, which does not include any of the previously
mentioned systems. In the future, this new benchmark should be useful. If you are
considering an upgrade, then try to find the CIW of your current system and the ones to which
you are considering upgrading.
For systems below these recommended minimum specifications, IBM states that you may use
them in environments that support a limited number of users and where longer server
initialization times can be tolerated.
Geac’s experience is that a small installation may be successful if you are beneath the
recommended processor levels. However, Geac recommends that you do not go below the
recommended memory requirements. When there is insufficient memory, WebSphere
performance is severely impaired. If you are considering an upgrade to improve WebSphere
performance, then monitor your memory usage carefully. It may be more effective to upgrade
the memory rather than the processor.
Older AS/400 models, before the 170 and 720 ranges, are liable to give poor WebSphere
performance. Consider installing WebSphere on older AS/400 systems only if they are
particularly large. Even so, the performance may be disappointing. Geac ran call.connect on
a Model S30 with a CPW of 999, yet the performance was not much better than a 170-2385
with a CPW of only 460.
5.2 Operating System/400 (OS/400)
Several aspects of OS/400 configuration are important to WebSphere performance. These
aspects are explained in the following sections.
5.2.1 SQL server job configuration
WebSphere applications make substantial use of Java Database Connectivity (JDBC). On the
iSeries, there are two commonly used JDBC drivers:
Toolbox driver: This is primarily used by Java applications that are not running on the
iSeries itself.
