What a difference a few years can make, eh? The key difference is that John can tell the doctor where the pain is. This is just like Oracle's wait interface telling you where the pain is, where the contention is, and where too much time is being spent. Ratio analysis is like diagnosing Johnny, whereas wait-event analysis is like working with John-a much faster, more precise, and more confident diagnosis.

* First, the doctor must know John's language and be able to listen to him. This is just like a firefighter knowing how to listen to Oracle, through Oracle's wait interface. This book will teach you how to listen to Oracle. But this is just the start.

* Second, even with an amazing diagnosis, to solve John's problem, the doctor must have a deep understanding of the human body and specifically in this case, the elbow. This is just like a performance specialist knowing Oracle internals. Knowing Oracle is suffering from intense library cache contention is good, but to solve the problem, you must understand Oracle internals enough to influence the situation to reduce the contention.