PriorityGraph: A Unified Programming Model for Optimizing Ordered Graph Algorithms

Many graph problems can be solved using ordered parallel graph algorithms that achieve significant speedup over their unordered counterparts by reducing redundant work. This paper introduces PriorityGraph, a new programming framework that simplifies writing high-performance parallel ordered graph algorithms. The key to PriorityGraph is a novel priority-based abstraction that enables vertices to be processed in a dynamic order while hiding low-level implementation details from the user. PriorityGraph is implemented as a language and compiler extension to GraphIt. The PriorityGraph compiler extension leverages new program analyses, transformations, and code generation to produce fast implementations of ordered parallel graph algorithms. We also introduce bucket fusion, a new performance optimization that fuses together different rounds of ordered algorithms to reduce synchronization overhead, resulting in 1.2$\times$ to 3$\times$ speedup over the fastest existing ordered algorithm implementations on road networks with large diameters. PriorityGraph achieves up to 3$\times$ speedup on six ordered graph algorithms over state-of-the-art frameworks and hand-optimized implementations (Julienne, Galois, and GAPBS) that support ordered algorithms.