Building Scalable NVM-based B+tree with HTM

Emerging on-volatile memory (NVM) opens an opportunity to build durable data structures. However, to build a highly efficient complex data structure like B+tree on NVM is not easy. We investigate the essential performance bottleneck for NVM-based B+tree. Even with a single-core CPU, the performance is limited by the atomic-write size which plays an essential role in the trade-off between the persistent overhead and keeping leaf node entries sorted. For the multi-core setting, the overlapping of concurrency and persistency is key to the system scalability.

Based on the analysis, we propose RNTree, a durable NVM-based B+tree using the hardware transactional memory (HTM). Our way of using HTM can actually address both problems mentioned above simultaneously. (1) HTM can use cache-line granularity to provide larger atomic-write size. Based on this, we propose a new slot-array approach which traces the order of entries in the leaf nodes while still reducing the number of persistent instructions. (2) With careful design, RNTree moves slow persistent instructions out of critical sections and proposes the dual slot array design, to extract more concurrency. For single thread, RNTree achieves 1.44×/4.2× higher throughput for single-key operations and range queries respectively. For multiple threads, the throughput of RNTree is 2.3× higher than state-of-the-art works.