NDLI: GigaHash: scalable minimal perfect hashing for billions of urls

Content Provider	ACM Digital Library
Author	Charles, Denis Mityagin, Anton Chellapilla, Kumar
Abstract	A minimal perfect function maps a static set of n keys on to the range of integers {0,1,2,.,n - 1}. We present a scalable high performance algorithm based on random graphs for constructing minimal perfect hash functions (MPHFs). For a set of n keys, our algorithm outputs a description of h in expected time O(n). The evaluation of h(x) requires three memory accesses for any key x and the description of h takes up 0.89n bytes (7.13n bits). This is the best (most space efficient) known result to date. Using a simple heuristic and Huffman coding, the space requirement is further reduced to 0.79n bytes (6.86n bits). We present a high performance architecture that is easy to parallelize and scales well to very large data sets encountered in internet search applications. Experimental results on a one billion URL dataset obtained from Live Search crawl data, show that the proposed algorithm (a)finds an MPHF for one billion URLs in less than 4 minutes, and (b) requires only 6.86 bits/key for the description of h.
Starting Page	1165
Ending Page	1166
Page Count	2
File Format	PDF
ISBN	9781595936547
DOI	10.1145/1242572.1242747
Language	English
Publisher	Association for Computing Machinery (ACM)
Publisher Date	2007-05-08
Publisher Place	New York
Access Restriction	Subscribed
Subject Keyword	Minimal perfect hashing Web search engine Perfect hash function Space efficient hash table
Content Type	Text
Resource Type	Article

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GigaHash: scalable minimal perfect hashing for billions of urls