Practical Massively Parallel Sorting

Abstract: Previous parallel sorting algorithms do not scale to the largest available machines, since they either have prohibitive communication volume or prohibitive critical path length. We describe algorithms that are a viable compromise and overcome this gap both in theory and practice. The algorithms are multi-level generalizations of the known algorithms sample sort and multiway mergesort. In particular our sample sort variant turns out to be very scalable. Some tools we develop may be of independent interest -- a simple, practical, and flexible sorting algorithm for small inputs working in logarithmic time, a near linear time optimal algorithm for solving a constrained bin packing problem, and an algorithm for data delivery, that guarantees a small number of message startups on each processor.