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Query-processing optimization strategies: feasible vs optimal solutions

This paper compares three strategies for reducing the number of external record retrievals in order to minimize query processing time. A generalized file organization is assumed which presents a problem not found when inverted file directories are used, i.e., the retrieval of surplus records because some addressing information is kept in the file itself. Given that all keys in a query need not be used for retrieval, what is the optimal set of keys to use? The “prime key word” and “minimum N/F” techniques are both greedy methods and so cannot guarantee an optimal solution since they consider only local optimization measures. The “minimum cost cover” technique, however, does yield the optimal solution because it considers the overall objective function.