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<p>The exact expression for the expected number of disk accesses required to retrieve a given number of records, called the Yao function, requires iterative computations. Several authors have developed approximations to the Yao function, all of which have substantial errors in some situations. We derive and evaluate simple upper and lower bounds that never differ by more than a small fraction of a disk access.</p>
database management systems; file organisation; errors; performance evaluation; database theory; block access estimation; database organization; disk accesses; record retrieval; Yao function; iterative computations; approximation; errors; upper bound; lower bound; access path selection; physical database design; performance estimation

A. Saharia and G. Diehr, "Estimating Block Accesses in Database Organizations," in IEEE Transactions on Knowledge & Data Engineering, vol. 6, no. , pp. 497-499, 1994.
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