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
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