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Extendible Hashing

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Encyclopedia of Database Systems

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. 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.

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  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.

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Author information

Authors and Affiliations

  1. Paradigm4, Inc., Waltham, MA, USA

    Donghui Zhang

  2. Aristotle University of Thessaloniki, Thessaloniki, Greece

    Yannis Manolopoulos

  3. University of Piraeus, Piraeus, Greece

    Yannis Theodoridis

  4. University of California-Riverside, Riverside, CA, USA

    Vassilis J. Tsotras

Authors
  1. Donghui Zhang
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  2. Yannis Manolopoulos
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  3. Yannis Theodoridis
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  4. Vassilis J. Tsotras
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Corresponding author

Correspondence to Donghui Zhang .

Editor information

Editors and Affiliations

  1. Georgia Institute of Technology College of Computing, Atlanta, GA, USA

    Ling Liu

  2. University of Waterloo School of Computer Science, Waterloo, ON, Canada

    M. Tamer Özsu

Section Editor information

  1. University of California-Riverside, Riverside, CA, USA

    Vassilis J. Tsotras

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Cite this entry

Zhang, D., Manolopoulos, Y., Theodoridis, Y., Tsotras, V.J. (2018). Extendible Hashing. In: Liu, L., Özsu, M.T. (eds) Encyclopedia of Database Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-8265-9_741

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