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Block access estimation for clustered data

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1 Author(s)
Ciaccia, P. ; Dipartimento di Elettronica, Inf. e Sistemistica, Bologna Univ., Italy

A method is proposed for dealing with nonuniform data distributions in database organizations in order to estimate the expected number of blocks containing the tuples requested by a query. When tuples with equal attribute value are not uniformly distributed over the blocks of secondary memory that store the relation, a clustering effect is observed. This can be detected by means of a single parameter, the clustering factor, which can be stored in the system catalog. The method can be applied to uniform data distributions as well, since it is shown that a uniform distribution can be viewed as a particular instance of a class of clustered distributions. In this case the proposed method allows considerable reduction of the number of computational steps needed to compute the estimated result

Published in:

Knowledge and Data Engineering, IEEE Transactions on  (Volume:5 ,  Issue: 4 )

Date of Publication:

Aug 1993

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