Figure 2-13. The v$session_wait view can also be used to list wait event details about all sessions waiting on a specific event. In this example, all four sessions are waiting for the operating system to return 16 blocks.

If you understand the instrumentation concept, are familiar with the three core wait event views, and use a methodical diagnosis framework, you are prepared to jump to the next level, which is performing an ORTA. Obviously, you need an understanding of what the wait events are telling you. Otherwise, you are like a doctor who hears what the patient is saying, but doesn't know enough to do anything about it. The upcoming chapters will provide you with the knowledge you need to take a stellar diagnosis and derive solutions that will directly attack the problem.

What is your response when someone asks you what you do for a living? Perhaps you simply say you work "in IT" or "with Oracle databases." It's very unlikely that you say something like, "Well, it's interesting you should ask. Today, I diagnosed a very complex Oracle database system. And you know what? I discovered that 75% of all the Oracle session wait time was because of latching issues. Upon closer inspection, I found the latch in question was the CBC latch! It makes sense, you know, because the server was completely CPU-bound, and there were two SQL statements generating tons of logical IO..."