Figure 9-18 graphically shows how adding more transaction processors can affect a system. If the bottleneck is IO, then the same general effect occurs when adding IO devices. Starting at point A, the performance is unacceptable and highly variable. By implementing addition transaction processors, the response time decreases (that is, improves), and the system is operating at point B. However, now the administrators have a choice. By controlling the workload (the arrival rate), they can allow more work to flow through the system without affecting response time. Point C shows this negligible effect on response time by allowing the arrival rate to increase. So, by adding more capacity (either more and/or faster transaction processors), the performance analyst once again has several options: decreased response time, increased workload, or a managed combination of both.

Figure 9-18. Shown is the response-time effect of increasing capacity by adding transaction processors (for example, CPU cores). By adding CPU cores, a new response-time curve takes effect (dotted line). The response time drops from point A to point B. By controlling the workload, performance can remain at point B, or by allowing the workload to increase to point C, the system can still maintain both improved response time and an increased workload.

Workload management can provide arguably the most elegant of all performance improvements. And of all the missed performance-improving opportunities, I would say better workload management has got to be near the top. While shifting workloads may not be a very satisfying technical challenge (though it can be), when the workload is better managed, peak workload and painful performance periods can be dramatically improved. And all this can occur without tuning Oracle, the application, or the operating system, and without any capital investment.