PMap: A Non-volatile Lock-free Hash Map with Open Addressing

Abstract

Non-volatile memory (NVM) is an emerging memory technology that provides data persistence and higher densities than conventional DRAM. The release of Intel Optane DC memory makes NVM a practical and testable technology. Hash maps are fundamental data structures that associatively map keys to values, offering constant time lookup. In this work, we designed a scalable, persistent hash map, PMap, optimized around large graph processing workloads. PMap is a lock-free non-volatile hash map with open addressing. Open addressing offers low memory overhead and improved cache locality when compared with node-based alternatives. Lock-freedom ensures scalable performance, and its nonblocking nature enables log-free persistence. Our hash map is supported by a non-blocking, parallel resize, which allows operations to be performed by other threads during a resize. In our performance tests, we found that our design outperformed state-of-the-art alternatives, averaging 3122x faster under Optane DC.