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Write-Combined Logging: An Optimized Logging for Consistency in NVRAM

Nonvolatile memory (e.g., Phase Change Memory) blurs the boundary between memory and storage and it could greatly facilitate the construction of in-memory durable data structures. Data structures can be processed and stored directly in NVRAM. To maintain the consistency of persistent data, logging is a widely adopted mechanism. However, logging introduces write-twice overhead. This paper introduces an optimized write-combined logging to reduce the writes to NVRAM log. By leveraging the fast-read and byte-addressable features of NVRAM, we can perform a read-and-compare operation before writes and thus issue writes in a finer-grained way. We tested our system on the benchmark suit STAMP which contains real-world applications. Experiment results show that our system can reduce the writes to NVRAM by 33%–34%, which can help extend the lifetime of NVRAM and improve performance. Averagely our system can improve performance by 7%–11%.