A Multi-hashing Index for hybrid DRAM-NVM memory systems

Hybrid memory systems composed of DRAM and Non-Volatile Memory (NVM) promise the capacity benefits of NVM and the low-latency benefits of DRAM. Most existing hash-based indexes are designed for NVM only and do not exploit the benefits of DRAM. In this paper, we proposed a novel hybrid DRAM-NVM persistent and concurrent hashing index, named Multi-Hashing Index (MuHash). MuHash uses a multi-hash function scheme to solve the cascading write problem of open-addressed hash-based indexes in NVM. It employs a Cuckoo Filter, an approximate membership query data structure, to prune unnecessary NVM accesses for improving read performance. To maximize throughput in multi-thread environments, MuHash also includes a fine-grained concurrency control mechanism. We implemented MuHash for Intel Optane DC Persist Memory, and single-core experiments shows that MuHash achieves up to 90% higher read throughput compared to state-of-the-art hash-based indexes. On multicore experiments, MuHash achieves near-linear scalability for all operations.