NIST

cuckoo hashing

(data structure)

Definition: A dictionary implemented with two hash tables, T1 and T2, and two different hash functions, h1 and h2. Each key, k, is either in T1[h1(k)] or T2[h2(k)]. A new key, k, is stored in T1[h1(k)]. If that location is already occupied by another key, l, the other key is moved to T2[h2(l)]. Keys are moved back and forth until a key moves to an empty location or a limit is reached. If the limit is reached, new hash functions are chosen, and the tables are rehashed. For tables that are a bit less than half full and with carefully chosen universal hashing functions, performance is good. A key is deleted by removing it from a table.

Generalization (I am a kind of ...)
hash table.

Aggregate parent (I am a part of or used in ...)
dictionary.

Aggregate child (... is a part of or used in me.)
array, hash function.

See also 2-left hashing.

Note: The name comes from the European cuckoo, whose young pushes other, competing eggs out of the nest.

Author: PEB

More information

Rasmus Pagh and Flemming Friche Rodler, Cuckoo Hashing, Proceedings of ESA 2001, Lecture Notes in Computer Science, vol. 2161, pages 121-?, 2001.
Generalized in Úlfar Erlingsson, Mark Manasse, and Frank McSherry, A cool and practical alternative to traditional hash tables, proc 7th Workshop on Distributed Data and Structures (WDAS'06), Santa Clara, CA, January 2006.


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Entry modified 30 March 2009.
HTML page formatted Tue May 6 13:48:55 2014.

Cite this as:
Paul E. Black, "cuckoo hashing", in Dictionary of Algorithms and Data Structures [online], Vreda Pieterse and Paul E. Black, eds. 30 March 2009. (accessed TODAY) Available from: http://www.nist.gov/dads/HTML/cuckooHashing.html