Estimation of Access Costs
We've seen how to estimate the
of a join. Now we look at estimating the
of processing a join.
Several factors influence the selection of an optimal strategy:
Physical order of tuples in a relation.
Presence of indices and type of index (clustering or not).
Cost of computing a temporary index for the sole purpose of processing one query.
We'll look at computing the expression
assuming no indices exist. We also let
Use of an Index
Sun Jul 26 17:45:14 PDT 1998