Creating the IO response-time graph is a little tricky because you never see response time solved for the number of devices (M). Looking at the response-time equation, we know every variable except for M. We know the response time because Oracle's wait interface provides the information to calculate the queue time (Qt). It turns out this formula cannot be solved using algebra, requiring an iterative approach to converge on an answer.9

Based on this exercise's AWR data, the various values gathered and derived were entered into OraPub's response-time graph template tool, resulting in the graph shown in Figure 9-16.10 The tool is very simple to use and requires only the data presented in this example.

Figure 9-16. Shown is the response-time graph for this exercise. It shows the service time, queue time, response time, and the arrival rate as reported from the AWR report.