Minimum cost selection of secondary indexes for formatted files

Abstract

Secondary indexes are often used in database management systems for secondary key retrieval. Although their use can improve retrieval time significantly, the cost of index maintenance and storage increases the overhead of the file processing application. The optimal set of indexed secondary keys for a particular application depends on a number of application dependent factors. In this paper a cost function is developed for the evaluation of candidate indexing choices and applied to the optimization of index selection. Factors accounted for include file size, the relative rates of retrieval and maintenance and the distribution of retrieval and maintenance over the candidate keys, index structure, and system charging rates. Among the results demonstrated are the increased effectiveness of secondary indexes for large files, the effect of the relative rates of retrieval and maintenance, the greater cost of allowing for arbitrarily formulated queries, and the impact on cost of the use of different index structures.