15.6 Index-Based Algorithms Sadiya Hameed ID: 206 CS257

Sadiya Hameed2 Clustering Indexes Clustering Indexes are indexes on an attribute or attributes such that all the tuples with a fixed value for the search key of this index appear on as few blocks as possible

Sadiya Hameed3 Index-Based Selection For clustering index on R.a: number of disk I/O’s will average B( R ) / V(R, a) Number may be higher cause Index not entirely in main memory Tuples spread over more blocks

Sadiya Hameed4 Index-Based Selection (cont’d) For non-clustering index on R.a: number of disk I/O’s will average T ( R ) / V(R, a) Number may be higher because May need to read some index blocks from disk Number could be lower because Some retrieved tuples appear on same block

Sadiya Hameed5 Joining by using an Index Natural Join R(X, Y) S(Y, Z) Number of disk I/O’s If R is clustered: B( R ) If R is not clustered: T( R )

Sadiya Hameed6 Joins using a Sorted Index Consider Natural Join R(X, Y) S(Y, Z) with Index on Y for either R or S zig-zag join If indexes are B-Tree and R and S are clustered Retrieval of tuples with given key has I/O’s proportional to the fractions of these two relations

Sadiya Hameed7 Questions