Size Estimation and Reduction Factors
Maximum # tuples in result is the product of the cardinalities of relations in the FROM clause.
Reduction factor (RF) associated with each term reflects the impact of the term in reducing result size. Result cardinality = Max # tuples * product of all RF’s.
- Implicit assumption that terms are independent!
- Term col=value has RF = 1/NKeys(I), given index I on col
- Term col1=col2 has RF = 1/MAX(NKeys(I1), NKeys(I2))
- Term col>value has RF = (High(I)-value)/(High(I)-Low(I))
WHERE term1 AND ... AND termk