An efficient multiprocessor merge algorithm

Abstract

An efficient algorithm for merging two memory-resident sorted lists is described. The algorithm is based on a novel low-cost partitioning algorithm that is used to split the two lists among an arbitrary number of processors in a way that ensures load balance during the merge. The algorithm has direct applications in memory-resident databases, as well as for handling record pointers in disk-resident databases. It may be used for parallel sorting, table access using multiple indexes, and parallel sort-merge joins. A feature of the partitioning algorithm is that it may itself be parallelized efficiently; the parallel implementation reduces partitioning time, which may become significant if the number of processors gets large. If p is the number of processors and N is the total number of elements in both runs combined, the serial and parallel versions of the partitioning algorithm require time O(p log (N/p)), and O(log p+log(N/p)), respectively.<>