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Cost Models

An important aspect of this course is
  • analysis of cost of various query methods
Cost can be measured in terms of
  • Time Cost: total time taken to execute method, or
  • Page Cost: number of pages read and/or written
Assumptions in our cost models:
  • memory (RAM) is "small", fast, byte-at-a-time
  • disk storage is very large, slow, page-at-a-time
  • every request to read/write a page results in a read/write
Trying to estimate costs with multiple concurrent ops and buffering is difficult!