A key statistic shown in the rtsysx.sql report is the Oracle CPU utilization consumption. During the 120-second interval, Oracle processes consumed only 8% of the total CPU available. This statistic is simply the Oracle CPU consumption divided by the host CPU time capacity. Figure 2-15 shows that Oracle processes consumed only 10 seconds of CPU. The total CPU capacity the host can provide is the number of CPU cores multiplied by the report interval. In this case, there is a single CPU core and the interval is 120 seconds, resulting in a total CPU capacity available of only 120 seconds. Therefore, the percentage of Oracle CPU consumed is 8%, or 10/(1*120), which is 8.33%. This simple statistic gives us a surprisingly useful understanding of this instance's host CPU impact. If this is the only instance running on the host, it also provides an operating system CPU utilization picture, without executing an operating system command. In this situation, this is the only instance; therefore, we would expect the operating system CPU utilization to be a few percentage points higher than 8%.

It may seem odd that a 120-second interval can show 621 seconds of wait time. This is very common in Oracle systems. The 621 seconds of wait time are the total wait time for all sessions during the 120-second interval. For example, if there were 1,000 sessions, and each session waited 1 second during the 120-second interval, then the total wait time would be 1,000 seconds. If 2,000 sessions each waited 2 seconds, then the total wait time would be 4,000 seconds. The more time processes wait, the more wait time. So one way to increase the wait time is to keep increasing the workload, which can be represented by the number of sessions or the work the sessions are doing.

If IO is an issue, you will certainly want to know if it's read- or write-focused. IO administrators can also benefit from knowing the type of IO load (read or write; single block or multiblock) Oracle is putting on the system. The Oracle IO-centric solutions are also very different based on the IO load type. An IO read issue can be minimized by keeping the more popular blocks in Oracle cache, whereas an IO write issue is minimized by core configuration issues, such as the number and size of the online redo logs.