Figure 9-17 graphically shows how tuning can affect a system. Starting at point A, the performance is unacceptable and highly variable. By tuning the application, Oracle, or the operating system, 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 the system without affecting the response time. Point C shows this negligible affect on response time by allowing the arrival rate to increase. So again, tuning provides the performance analyst with several options: decreased response time, increased workload, or a managed combination of both!

Figure 9-17. Shown is the response time effect of tuning. By tuning, a new response-time curve takes effect (dotted line), and 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.

When additional or faster CPUs or IO devices are added to a system, we have effectively increased capacity. For example, because the old CPUs were replaced with CPUs that are twice as fast, instead of a SQL statement consuming 4 seconds of CPU, it now consumes only 2 seconds of CPU. Or perhaps six additional CPU cores were added. Thinking about the basic utilization formula of requirements divided by capacity, if capacity increases and the requirements remain the same, then the utilization must decrease. The only way to increase the utilization is to increase the requirements. One way to do this is to increase the workload (the arrival rate). So, by increasing capacity, we have provided the basic performance-enhancing options of decreased response time, increased throughput, or some combination of both.