While Table 9-4 is a numeric representation of our analysis flow (and success), Figure 9-36 is a graphical representation. Based on logical IOs, Figure 9-36 shows the initial and final response-time curves and the respective arrival rates. Technical and nontechnical people alike should be able to easily grasp that the situation is much better now at point B than when we started at point A. Adding that there is now more room for growth and that the users are also performing more real work (SQL statement execution) will add a final punch to our presentation.

Figure 9-36. Shown is a logical IO-focused response-time curve highlighting and contrasting the initial performance situation (point A) to the final performance situation (point B). This response-time curve indicates a very successful performance effort because fewer resources are required for a single logical IO (service time decreased), users are putting less of a load on the system (not shown: while their work productivity has increased), and the database server's CPU subsystem can now accommodate a much larger future growth.

When adding the status column index, we anticipated only a 3% decrease in CPU utilization, but in reality, there was a 13% drop! Always try to be conservative, but in this case, the anticipated performance impact was simply wrong. We got lucky because many other SQL statements were impacted (for the better) in addition to the four we targeted. Because we did not analyze all possible affected SQL statements, there could have easily been other statements negatively impacted, eliminating any performance gain achieved from our targeted efforts.