Algorithms seminar: Rasmus Pagh

Date: April 13, 2007 (Friday) at 14:15 to 15:00

Title: Linear Probing with Constant Independence

Hashing with linear probing dates back to the 1950s, and is among the most studied algorithms. In recent years it has become one of the most important hash table organizations since it uses the cache of modern computers very well. Unfortunately, previous analyses rely either on complicated and space consuming hash functions, or on the unrealistic assumption of free access to a truly random hash function. Already Carter and Wegman, in their seminal paper on universal hashing, raised the question of extending their analysis to linear probing. However, we show in this paper that linear probing using a pairwise independent family may have expected logarithmic cost per operation. On the positive side, we show that 5-wise independence is enough to ensure constant expected time per operation. This resolves the question of finding a space and time efficient hash function that provably ensures good performance for linear probing.

Joint work with Anna Pagh and Milan Ruzic

To appear at STOC 2007

Room: E:2405

Last modified Dec 9, 2011 12:59 pm