A Bulk-Parallel Priority Queue in External Memory with STXXL

We propose the design and an implementation of a bulkparallel external memory priority queue to take advantage of both sharedmemory 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.