Chapter 10: Performance Modeling: Tools for Predicting Performance

Chapter 10

Performance Modeling: Tools for Predicting Performance

TCA is the scientific method of determining server capacity establish a hypothesis, and then run an experiment with live hardware and real or projected usage data to determine the validity of your expected result. Using this method, basic capacity planning and real-time evaluation of existing systems can be done with an acceptable degree of certainty. Provided the usage data, hardware, and network resources are available to test, TCA can also be used to anticipate changes in load and cost, and to determine where adjustments can be made in the name of either higher performance or lower financial impact.

When an established server s load grows to the point where performance is reduced, the most common solution is to add more resources, with the expectation that things like additional processor capacity or bandwidth will have a direct impact on the performance problem. Although this can be expensive, it is usually considered a good problem to have. A system that has reached its critical limit for performance is probably generating revenue, or at least experiencing high traffic. Additional hardware costs are justifiable on the surface, and hardware installation rarely involves a major reconfiguration of the server s software components. The expectation is that users will not experience an interruption in their service just an improvement in its response time.

The attitude that more hardware solves the problem can get software engineers and network managers in trouble, however, because adding more physical resources does not always address the real issue.

For example, consider an e-commerce server that is taking too long to process order handling, and generating errors for some users who try to place an order. The IT staff may decide that because their processor load is often near maximum, the bottleneck is the result of a lack of hardware resources. However, this bottleneck in performance might be caused by the server application: perhaps the order processing application is only designed to handle a finite number of simultaneous open order input transactions. If this aspect of the application is not anticipated in TCA evaluations, the TCA results will not show that increasing processor speed will have no impact on the problem.