Partitioned Parallel Radix Sort

Abstract

Load balanced parallel radix sort solved the load imbalance problem present in parallel radix sort. Redistributing the keys in each round of radix, each processor has exactly the same number of keys, thereby reducing the overall sorting time. Load balanced radix sort is currently known the fastest internal sorting method for distributed-memory multiprocessors. However, as the computation time is balanced, the communication time emerges as the bottleneck of the overall sorting performance due to key redistribution. We present in this report a new parallel radix sorter that solves the communication problem of balanced radix sort, called partitioned parallel radix sort. The new method reduces the communication time by eliminating the redistribution steps. The keys are first sorted in a top-down fashion (left-to-right as opposed to righttoleft) by using some most significant bits. Once the keys are localized to each processor, the rest of sorting is confined within each processor, hence eliminating the need for global redistribution of keys. It enables well balanced communication and computation across processors. The proposed method has been implemented in three different distributedmemory platforms, including IBM SP2, CRAY T3E, and PC Cluster. Experimental results with various key distributions indicate that partitioned parallel radix sort indeed shows significant improvements over balanced radix sort. IBM SP2 shows 13% to 30% improvement while Cray/SGIT3E does 20% to 100% in execution time. PC cluster shows over 2.5 fold improvement in execution time.KeywordsExecution TimeCommunication TimeLoad ImbalanceSorting TimeRadix SortThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.