NVRAM-aware logging in transaction systems

Emerging byte-addressable, non-volatile memory technolo- gies (NVRAM) like phase-change memory can increase the capacity of future memory systems by orders of magnitude. Compared to systems that rely on disk storage, NVRAM- based systems promise significant improvements in perfor- mance for key applications like online transaction process- ing (OLTP). Unfortunately, NVRAM systems suffer from two drawbacks: their asymmetric read-write performance and the notable higher cost of the new memory technologies compared to disk. This paper investigates the cost-effective use of NVRAM in transaction systems. It shows that us- ing NVRAM only for the logging subsystem (NV-Logging) provides much higher transactions per dollar than simply replacing all disk storage with NVRAM. Specifically, for NV-Logging, we show that the software overheads associated with centralized log buffers cause performance bottlenecks and limit scaling. The per-transaction logging methods de- scribed in the paper help avoid these overheads, enabling concurrent logging for multiple transactions. Experimental results with a faithful emulation of future NVRAM-based servers using the TPCC, TATP, and TPCB benchmarks show that NV-Logging improves throughput by 1.42 - 2.72x over the costlier option of replacing all disk storage with NVRAM. Results also show that NV-Logging performs 1.21 - 6.71x better than when logs are placed into the PMFS NVRAM-optimized file system. Compared to state-of-the- art distributed logging, NV-Logging delivers 20.4% through- put improvements.