The total request time is more formally called response time and is discussed in the next section. The units for queue time are the same as for service time, such as milliseconds per logical IO.

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.