•For each plan considered, must
estimate cost:
–Must estimate cost of
each operation in plan tree.
•Depends on input
cardinalities.
–Must estimate size of result for each operation in tree!
•Use information about the input
relations.
•For selections and joins, assume
independence of predicates.
•We’ll discuss the System R cost estimation approach.
–Very inexact, but works ok in practice.
–More sophisticated techniques known now.