Estimating block transfers and join sizes

Abstract

In this paper we provide estimates of the number of sequential and random block accesses required for retrieving a number of records of a file when the distribution of records in blocks of secondary storage is not uniform. We show how these results apply to estimating sizes of joins and semi-joins. We prove that when the uniformity of placement assumption is not satisfied it often leads to pessimistic estimates of performance. Finally we show a recursive estimation of the probability distribution of the number of blocks containing a given number of records.