The Effect of Local Sort on Parallel Sorting Algorithms

We show the importance of sequential sorting in the context of in memory parallel sorting of large data sets of 64 bit keys. First, we analyze several sequential strategies like Straight Insertion, Quick sort, Radix sort and CC-Radix sort. As a consequence of the analysis, we propose a new algorithm that we call Sequential Counting Split Radix sort, SCS-Radix sort. SCS-Radix sort is a combination of some of the algorithms analyzed and other new ideas. There are three important contributions in SCS-Radix sort. First, the work saved by detecting data skew dynamically. Second, the exploitation of the memory hierarchy done by the algorithm. Third, the execution time stability of SCS-Radix when sorting data sets with different characteristics. We evaluate the use of SCS-Radix sort in the context of a parallel sorting algorithm on an SGI Origin 2000. The parallel algorithm is from 1:2 to 45 times faster using SCSRadix sort than using Radix sort or Quick sort.