The database server bottleneck is the IO subsystem. Simply put, Oracle's IO read requirements have exceeded the IO subsystem's read capacity. We will expect our response-time graph to reflect the general queue time increase of an IO bottleneck, which has a continual and steady increase in queue time until the elbow of the curve is reached, and then response time skyrockets.

While the wait event situation, shown in Figure 9-14, looks like an IO bottleneck, especially with the 20 ms average db file scattered read time, there could be also be a CPU bottleneck. To double-check, calculate both the operating system and the Oracle CPU utilization. Using Figure 9-15 to calculate Oracle CPU requirements and considering both server process (DB CPU of 2,065.87 seconds) and background process (background cpu time of 25.95 seconds) CPU consumption, the total instance CPU consumption is 2,091.82 seconds.8 The database server CPU capacity is based on the four CPU cores and the 60-minute reporting interval.

Figure 9-14. Shown is a snippet from both v$system_event (wait events) and v$sys_time_model (v$sys_time_model, DB CPU). Oracle does not include background CPU when calculating "CPU time."