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ALGORITHMICA
2008

Optimality in External Memory Hashing

13 years 11 months ago
Optimality in External Memory Hashing
Hash tables on external memory are commonly used for indexing in database management systems. In this paper we present an algorithm that, in an asymptotic sense, achieves the best possible I/O and space complexities. Let B denote the number of records that fit in a block, and let N denote the total number of records. Our hash table uses 1+O(1/ B) I/Os, expected, for looking up a record (no matter if it is present or not). To insert, delete or change a record that has just been looked up requires 1 + O(1/ B) I/Os, amortized expected, including I/Os for reorganizing the hash table when the size of the database changes. The expected external space usage is 1 + O(1/ B) times the optimum of N/B blocks, and just O(1) blocks of internal memory are needed. Key words: External memory, dictionary, hashing, index
Morten Skaarup Jensen, Rasmus Pagh
Added 24 Dec 2010
Updated 24 Dec 2010
Type Journal
Year 2008
Where ALGORITHMICA
Authors Morten Skaarup Jensen, Rasmus Pagh
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