Dynamic testing

The preceding tests were conducted independently, with processors units assigned up front. There were no changes to the resources throughout the tests. We carried out the testing in this way to obtain an accurate measurement of response time for comparison.

However, we also wanted to determine how our scenario would respond to dynamic allocation of resources. This effect can be observed by repeating the test with a longer test duration, so we set the schedule to stop after 20 minutes. This would give ample time for ramp up and a stable period for testing the dynamic allocation of processing units.

So, we reset the processing units back to 1 using the Web SM tool. The test was then started and processor utilization was monitored with lparstat. After the test had passed the ramp-up phase and settled down, we dynamically assigned more processing units to the LPAR. We made similar observations, in which processing utilization dropped to around 40% after we increased the processing units to 2.8, as before.

Improved response time was observed, as shown in the average page response time chart displayed in Figure 10-23.

Figure 10-23 Impact of dynamic resource change to page response

The arrow on the chart indicates the point where more processing units were allocated to this LPAR. Although the improvement in response time was not as significant as the processing utilization, it does show the trend and the effect of dynamically allocating more processing units "on the fly".

This scenario has shown that processor units can be dynamically added to a running WebSphere environment for improved processor utilization and response time. The improvement in response time will vary from application to application, and our Trade 6.1 application has room for improvement-but it does illustrate that WebSphere Application Server can take advantage of extra processor capacity without any changes.

As you can see, it is possible to monitor processor utilization in a WebSphere Application Server environment and run a script that will add more processing units to the LPAR when processor utilization hits a certain threshold. It is also possible to remove processing units if needed in a different LPAR. You can leverage the virtualization capability of POWER5 in an On Demand WebSphere Application Server environment.