Encyclopedia of Database Systems

2018 Edition
| Editors: Ling Liu, M. Tamer Özsu

Extendible Hashing

  • Donghui Zhang
  • Yannis Manolopoulos
  • Yannis Theodoridis
  • Vassilis J. Tsotras
Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-8265-9_741

Definition

Extendible hashing is a dynamically updateable disk-based index structure which implements a hashing scheme utilizing a directory. The index is used to support exact match queries, i.e., find the record with a given key. Compared with the B+-tree index which also supports exact match queries (in logarithmic number of I/Os), extendible hashing has better expected query cost O(1) I/O. Compared with linear hashing, extendible hashing does not have any overflow page. Overflows are handled by doubling the directory which logically doubles the number of buckets. Physically, only the overflown bucket is split.

Historical Background

The extendible hashing scheme was introduced by [1]. A hash table is an in-memory data structure that associates keys with values. The primary operation it supports efficiently is a lookup: given a key, find the corresponding value. It works by transforming the key using a hash function into a hash, a number that is used as an index in an array to...

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Recommended Reading

  1. 1.
    Fagin R, Nievergelt J, Pippenger N, Strong HR. Extendible hashing: a fast access method for dynamic files. ACM Trans Database Syst. 1979;4(3):315–44.CrossRefGoogle Scholar
  2. 2.
    Schneider DA, DeWitt DJ. Tradeoffs in processing complex join queries via hashing in multiprocessor database machines. In: Proceedings of the 16th International Conference on Very Large Data Bases; 1990. p. 469–80.Google Scholar

Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  • Donghui Zhang
    • 1
  • Yannis Manolopoulos
    • 2
  • Yannis Theodoridis
    • 3
  • Vassilis J. Tsotras
    • 4
  1. 1.Paradigm4, Inc.WalthamUSA
  2. 2.Aristotle University of ThessalonikiThessalonikiGreece
  3. 3.University of PiraeusPiraeusGreece
  4. 4.University of California-RiversideRiversideUSA

Section editors and affiliations

  • Vassilis J. Tsotras
    • 1
  1. 1.University of California-RiversideRiversideUSA