Analysis of the Search Performance of Coalesced Hashing

An analysis is presented of the coalesced hashing method, m which a portion of memory (called the address region) serves as the range of the hash function while the rest of memory (called the cellar) Is devoted solely to storing records that collide when inserted. If the cellar should get full, subsequent colliders must be stored in empty slots in the address region and thus may cause later collisions. Varying the relative size of the cellar affects search performance. The main result of this paper expresses the average search tunes as a function of the number of records and the cellar size, solving a long-standing open problem. These formulas are used to pick the cellar size that leads to optimum search performance, and tt is shown that this "tuned" method outperforms several well-known hashing schemes A discussion of past work on coalesced hashing and a generalization of the method to nonuniform hash functions conclude the paper Categories and SubJect Descriptors E 2 [Data]. Data Storage Representations--hash-table representations; F 2 2 [Analysis of Algorithms and Problem Complexity]Nonnumencal Algorithms and Problems--sorting and searching; G 2 1 [Discrete Mathematics] Combinatoncs--generating functions', permutations and combinations, recurrences and difference equauons; G.3 [Mathematics of Computing]: Probability and Statistlcs--i andom number generat:on, H 3 3 [Information Storage and Retrieval]. Information Search and Retrieval--search process General Terms. Algorithms, Performance, Theory Additional