CHAPTER 12Hash Joins
Before saying anything about the method that the optimizer uses to estimate the cost of a hash join, I shall describe the mechanics. There are two good reasons for doing this. First, the mechanism is not commonly known; second, you have to know the mechanism before you can hope to guess how the cost calculation works.
In all previous chapters, I have disabled CPU costing (the 9i system statistics feature) and worked with a manual workarea_size_policy rather than using the automatic option introduced in 9i. This is often a reasonable strategy to adopt because it doesn't materially affect the work that the optimizer does—until you get to hashing and sorting.
In the next two chapters, therefore, I shall be covering the four ...
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