Multi-Clock Snapshot Isolation Concurrency Control for NVM Database

Abstract

Multi-Clock Snapshot Isolation (MCSI) is a concurrency control mechanism that implements snapshot isolation on a single-layer Non-Volatile Memory (NVM) database. It stores a single copy of data by using multi-version storage to ensure durability and runtime access. With multi-clock transaction timestamp assignment, MCSI can efficiently generate snapshots with vector clocks and use per-thread transaction status arrays to identify uncommitted versions in NVM. For evaluation, we compared MCSI with the PostgreSQL-style concurrency control used in the single-layer NVM database N2DB. The maximum transaction throughput of MCSI is 101%–195% higher than that of N2DB for the YCSB workloads, and 25%–49% higher for the TPC-C workloads. Moreover, the transaction latency of MCSI remains relatively stable as the thread count increases. With 18 worker threads, the average transaction latency of MCSI is 65%–84% lower than that of N2DB for the YCSB workloads and 16%–43% lower for the TPC-C workloads.