Hashing with Overflow Indexing

Abstract

A hash structure, Overflow Indexing (OVI), using an index for the overflows is presented. The index contains one entry (key, bucket number) for each overflow. Formulas for computing the expected number of entries in the index and the standard deviation are derived and the numerical results obtained using these formulae are presented in a graph. It is concluded that storing the index in the main memory when operating on the file is feasible for small to medium-sized, and sometimes even large files. The number of probes for both a successful and unsuccessful search is one. Deletion requires two probes and insertion two or three probes. Details of OVI are presented and illustrated by simulation experiments. The structure of the index is discussed and one possible structure, hashing with dynamic buckets, is presented.