CHAPTER 2Tablescans

At first sight, you might think that there couldn't be a lot to say about tablescans, but you may be in for a surprise. Since the cost calculations for tablescans are nice and simple, I thought I'd use them in this early chapter to demonstrate the four different strategies for cost based optimization that have evolved over the years, briefly outlined here:

  • Traditional: Simple counting of read requests
  • System statistics (1): Accounting for size and time of read requests
  • System statistics (2): Accounting for CPU costs, and size and time of read requests
  • System statistics (3): Accounting for caching, CPU costs, and size and time of read requests

The traditional method appeared in Oracle 7, and has been enhanced continuously ...

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