Storage management in the NVRAM era

Abstract

Emerging nonvolatile memory technologies (NVRAM) offer an alternative to disk that is persistent, provides read latency similar to DRAM, and is byte-addressable. Such NVRAMs could revolutionize online transaction processing (OLTP), which today must employ sophisticated optimizations with substantial software overheads to overcome the long latency and poor random access performance of disk. Nevertheless, many candidate NVRAM technologies exhibit their own limitations, such as greater-than-DRAM latency, particularly for writes. In this paper, we reconsider OLTP durability management to optimize recovery performance and forward-processing throughput for emerging NVRAMs. First, we demonstrate that using NVRAM as a drop-in replacement for disk allows near-instantaneous recovery, but software complexity necessary for disk (i.e., Write Ahead Logging/ARIES) limits transaction throughput. Next, we consider the possibility of removing software-managed DRAM buffering. Finally, we measure the cost of ordering writes to NVRAM, which is vital for correct recovery. We consider three recovery mechanisms: NVRAM Disk-Replacement, In-Place Updates (transactions persist data in-place), and NVRAM Group Commit (transactions commit/persist atomically in batches). Whereas In-Place Updates offers the simplest design, it introduces persist synchronizations at every page update. NVRAM Group Commit minimizes persist synchronization, offering up to a 50% throughput improvement for large synchronous persist latencies.