Looking at the classic utilization formula, you see that utilization can increase if the service time, the queue time, or both increase. As the classic utilization formula indicates, and as Figure 9-7 demonstrates occurs in CPU-intensive Oracle systems with a consistent workload mix, when utilization increases, it is because the arrival rate (the workload) is increasing, not because service time is increasing.

Surely, the total service time is increasing with each arrival, but the service time per arrival (called simply the service time) remains roughly the same. It is easy to get the two terms confused. We know that when the workload increases, the total CPU consumption increases. But along with the CPU consumption increase comes a workload increase. The two offset each other, keeping the service time the same while the utilization increases.

When CPU-intensive Oracle algorithms begin to break down, you will notice that service time starts to increase as the arrival rate increases. If you look ahead to Figure 9-9, you will see a slight service time upward slope. As discussed back to Chapter 3, the CPU-intensive Oracle latching acquisition algorithm, with its combination of spinning and sleeping, does a tremendous job of limiting the increase in service time as the workload increases. What you feel and what users feel when performance begins to degrade is probably queue time increasing, rather than service time increasing.