Oracle has made CPU consumption details available for many years, at both the session and instance levels. It's just that CPU consumption has not been classified by DBAs and used in a response time-focused or OraPub 3-circle analyses. The benefits to using the instance statistic views (v$sesstat and v$sysstat) are that they are available on any Oracle release and are familiar to most DBAs. The negatives are that the statistics are not guaranteed to be updated until after a SQL statement completes, and when a session disconnects, all the session-level statistics (v$sesstat) vanish. Usually, this does not present a problem with a large multiuser Oracle system. However, with a batch-centric workload with only a few massive resource-consuming SQL statements running, it can muddy any Oracle analysis.

In the instance statistic views, Oracle provides only total CPU consumption. It does not differentiate between server process time and background process time.2 But if a background process is consuming an unusually large portion of the CPU, this can be easily seen from an operating system perspective. Figure 5-1 shows statistic 12, which is the total CPU consumption for the Oracle instance since instance startup. This includes all Oracle server processes and (we hope) all the background processes. The figure is in centiseconds. To convert to seconds, simply divide the queried value by 100. The example shown in Figure 5-1 has consumed 734.20 seconds (73420/100) of CPU time since it last started.

Figure 5-1. Since this instance has started, it has consumed 734 seconds of CPU. Statistic 12 from the classic instance statistics view v$sysstat contains the CPU time, in hundredths of a second, since the instance has started.