Parallel database sorting

Abstract

Sorting in database processing is frequently required through the use of Order By and Distinct clauses in SQL. Sorting is also widely known in computer science community at large. Sorting in general covers internal and external sorting. Past published work has extensively focused on external sorting on uni-processors (serial external sorting), and internal sorting on multi-processors (parallel internal sorting). External sorting on multi-processors (parallel external sorting) has received surprisingly little attention; furthermore, the way current parallel database systems do sorting is far from optimal in many scenarios. In this paper, we present a taxonomy for parallel sorting in parallel database systems, which covers five sorting methods: namely parallel merge-all sort, parallel binary-merge sort, parallel redistribution binary-merge sort, parallel redistribution merge-all sort, and parallel partitioned sort. The first two methods are previously proposed approaches to parallel external sorting which have been adopted as status quo of parallel database sorting, whereas the latter three methods which are based on redistribution and repartitioning are new that have not been discussed in the literature of parallel external sorting. Performance of these five methods is investigated and the results are reported.