Supporting Random Access in Files of Variable Length Records

: We consider the problem of providing a random access index to a file of variable length records. For a file of N bits and \Theta(N ) records the index we describe requires O((N log log N )= log N) = o(N ) bits, and access to any record is possible after O(logN ) bit accesses in the index and the file itself. This compares favourably with the \Theta(N log N ) space that would be required by a conventional index with the same access bound. Jacobson has also presented an O((N log log N )= log N ) space method of indexing; our method is simpler and leads to an implementation that is suitable for practical applications. Keywords: data structures, file structures, analysis of algorithms. 1 Introduction We suppose that a file of variable length records contains a total of N bits and p records; that the records are numbered sequentially from zero to p \Gamma 1; and that it is necessary to be able to efficiently access any record of the file given only an ordinal record number. The problem..