Index Tuning Conventional index

Overview

Duplicate keys

Dense index, one way to implement? Query –Look for the first K, then search forward Duplicate keys

Dense index, better way? Duplicate keys Each pointer points to the first of records with key K Query –Find the first occurrence, then move forward

Sparse index, one way? Duplicate keys careful if looking for 20 or 30! Find the last index entry with key <=K Then, search backward until coming to the first entry or meeting an index entry E 2 with key strictly less than k

Sparse index, another way? Duplicate keys – place first new key from block

Duplicate values, primary index Index may point to first instance of each value only File Index Summary a a a b 

Deletion from sparse index

Deletion from sparse index – delete record 40

Deletion from sparse index – delete record 30 40

Deletion from sparse index – delete records 30 &

Deletion from dense index

Deletion from dense index – delete record 30 40

Insertion, sparse index case

Insertion, sparse index case – insert record our lucky day! we have free space where we need it!

Insertion, sparse index case – insert record Illustrated: Immediate reorganization In principle, we may have had to slide every record to the end of the file Variation: – insert new block (chained file) – update index

Insertion, sparse index case – insert record overflow blocks (reorganize later...) No index entry for overflow blocks, which is considered as an extension of data block

Insertion, dense index case Similar Often more expensive...

summary