Consistent RDMA-Friendly Hashing on Remote Persistent Memory

Coalescing RDMA and Persistent Memory (PM) delivers high end-to-end performance for networked storage systems, which requires rethinking the design of efficient hash structures. In general, existing hashing schemes separately opti-mize RDMA and PM, thus partially addressing the problems of RDMA Access Amplification and High-Overhead PM Consistency. In order to address these problems, we propose a continuity hashing, which is a "one-stone-two-birds" design to optimize both RDMA and PM. The continuity hashing leverages a fine-grained contiguous shared region, called SBuckets, to provide standby positions for the neighbouring two buckets in case of hash collisions. In the continuity hashing, remote read only needs a single RDMA read to directly fetch the home bucket and the neighbouring SBuckets, which contain all the positions of maintaining a key-value item, thus alleviating RDMA access amplification. Continuity hashing further leverages indicators that can be atomically modified to support log-free PM consistency for all the write operations. Evaluation results demonstrate that compared with state-of-the-art techniques, continuity hashing achieves high throughput, low latency and the smallest number of PM writes with acceptable load factors.