Optimal multi-block read schedules for partitioned signature files

Abstract

Queries on partitioned signature files, namely Quick Filter (QF), can lead to retrieve from disk a large number of blocks, depending on the specific query pattern. In order to reduce the overall retrieval time, we consider multi-block read schedules that, provided contiguous allocation of blocks of the file on disk surface is guaranteed by the storage system, transfer more than one block at a time. We show that, for any signature query and buffer size, there always exists an optimal schedule whose reads all have the same size, and that such a constant size (CS) schedule can be determined in a time logarithmic in the number of blocks to be retrieved. We then provide analytical results for the expected performance of QF using CS schedules and compare QF with other, sequential-based, signature file organizations. Finally, we suggest how our approach can also be of interest for other file organizations based on multi-attribute hashing.

This work has been partially supported by Italian CNR, under contract no. 94.00388.CT12, and by ESPRIT LTR project no. 9141, HERMES (Foundations of High Performance Multimedia Information Management Systems).