Understanding how Oracle collects time is not only fascinating, but it also gives you a greater appreciation for the Oracle wait interface. You'll have a better idea of how the wait interface works, which provides you with a higher level of confidence during analysis and when presenting your results. You will also begin to use the instrumentation in creative and highly effective ways.

We must get creative to see how Oracle instruments its kernel code. Since we are not Oracle kernel developers, we obviously do not have access to Oracle's kernel code. But all is not lost! By tracing an Oracle process through the operating system, we can easily observe how Oracle has instrumented it code. The depth of knowledge you gain from doing this yourself is amazing.

The Linux trace command is strace. On Solaris, the command is truss. See your operating system documentation for its corresponding tracing command. When you issue the appropriate command for your operating system, the tracing immediately begins to spew forth output and continues until the process ends or you break out of the trace.