Hierarchic index sequential search with optimal variable block size and its minimal expected number of comparisons
Multilevel indexes are intensively used for accessing records in files. The search costs can considerably be reduced by selecting the number of levels and the size of the index at each level optimally. In this paper a multilevel and variable size index design strategy is developed which minimizes the expected number of comparisons. Its performance is evaluated in dependence of the number of levels for unsuccessful and successful search. A method to determine the number of levels which minimizes the expected number of comparisons is presented. The number of index entries and index files is given. The relevance of the results for jump searching is indicated. As an asymptotic upper bound for the minimal number of comparisons in an index sequential search the expression log2n +0.5 log2log2n is derived for n=( i 2i ).
KeywordsBlock Length Index File Successful Search Level Search Dimensional Search
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