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C H A P T E R

14

Indexing

Solutions for the Pratie Exerises of Chapter 14

Pratie Exerises

14.1

Answer:

Reasons for not keeping indies on every attr ibute inlude:



Ever y index requires additional

CPU

time and disk

I/O

overhead dur ing

inser ts and deletions.



Indies on non-pr imary keys might have to be hanged on updates, al-

though an index on the pr imary key might not (t his is beause updates

typially do not modify the primar y-key attributes).



Eah extra index requires additional storage spae.



For quer ies whih involve onditions on several searh keys, eieny

might not be bad even if only some of the keys have indies on t hem.

Therefore, database performane is improved less by adding indies when

many indies already exist.

14.2

Answer:

In general, it is not possible to have two pr imary indies on the same relation

for dierent keys beause the tuples in a relation would have to be stored in

dierent order to have the same values stored together. We ould aomplish

this by storing the relation twie and dupliating all values, but for a entralized

system, this is not eient.

81

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