* Significant queuing begins to occur near the elbow of the curve, which happens between 80% to 90% depending on the number of CPU cores. When evaluating alternative firefighting solutions, we want to be nowhere near the elbow of the curve!

When an Oracle database server CPU subsystem is heavily utilized, we know performance will be significantly degraded. Knowing the degree of "badness" is not important when evaluating alternative firefighting solutions. So, when performing our ORTA, it is not a problem to abstract and simply call this value CPU service time.

When IO times are gathered using Oracle's wait interface, from Oracle's vantage point, it is actually more of an IO response time. When Oracle issues an IO request to the operating system, it waits until the IO request is satisfied. When the IO subsystem processes the IO request, there is service time (perhaps transferring the data) and queue time (perhaps disk latency and head movement). The gettimeofday system call Oracle issues does not distinguish IO service and queue time, and therefore Oracle has no way of knowing the classification. But just as with CPU time, this does not present a problem, primarily because as performance analysts, we are interested in how long an IO call takes. The time components of the call can be of interest, but it's the total time-the response time-we need to know.