A bulk-parallel priority queue in external memory with STXXL

Abstract

We propose the design and an implementation of a bulk parallel external memory priority queue to take advantage of both shared-memory parallelism and high external memory transfer speeds to parallel disks. To achieve higher performance by decoupling item insertions and extractions, we offer two parallelization interfaces: one using “bulk” sequences, the other by defining “limit” items. In the design, we discuss how to parallelize insertions using multiple heaps, and how to calculate a dynamic prediction sequence to prefetch blocks and apply parallel multiway merge for extraction. Our experimental results show that in the selected benchmarks the priority queue reaches 64% of the full parallel I/O bandwidth of SSDs and 49% of rotational disks, or the speed of sorting in external memory when bounded by computation.