Cost-Based Oracle Fundamentals

CHAPTER 1What Do You Mean by Cost?

You have to be a little careful when you talk about the cost of an SQL statement because it's very easy to use the word in two different ways simultaneously. On one hand, you may be thinking about the magic number generated by a tool such as explain plan; on the other, you may be thinking about the actual resource consumption as a statement executes. In theory, of course, there ought to be a nice, simple relationship between the two, and it shouldn't be necessary to be so fussy about the meaning.

In this book, the word cost will always mean the result of the calculation performed by the optimizer. The purpose of the book is to explain the main features of how the optimizer does the calculations that produce ...