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Cost Models (cont)

In developing cost models, we also assume:
  • a relation is a set of r tuples, with average size R bytes
  • the tuples are stored in b data pages on disk
  • each page has size B bytes and contains up to c tuples
  • the tuples which answer query q are contained in bq pages
  • data is transferred disk↔memory in whole pages
  • cost of disk↔memory transfer Tr/w is very high

[Diagram:Pics/scansortproj/file-struct0.png]