Efficient Hardware-assisted Logging with Asynchronous and Direct-Update for Persistent Memory

Abstract

Supporting atomic durability in emerging persistent memory requires data consistency across potential system failures. For atomic durability support in the non-volatile memory, the traditional write-ahead log (WAL) technique has been employed to guarantee the persistency of logs before actual data updates. Based on the WAL mechanism, recent studies proposed HWassisted logging techniques with undo, redo, or undo+redo principles. The HW log manager allows the overlapping of log writing and transaction execution, as long as the atomicity invariant can be satisfied. Although the efficiency of both log and data writes must be optimized, the prior work exhibit trade-offs in performance under various access patterns. The undo approach experiences performance degradation due to synchronous inplace data updates since the log contains only the old values. On the other hand, the undo+redo approach stores both old and new values, and does not require synchronous in-place data updates. However, the larger log size increases the amount of log writes. The prior redo approach demands extra NVM read bandwidth for indirectly updating in-place data from the new values in logs. To overcome the limitations of the previous approaches, this paper proposes a novel redo-based logging (ReDU), which performs direct and asynchronous in-place data update to NVM. ReDU exploits a small region of DRAM as a write-cache to remove NVM writes from the critical path. The experimental results show that the proposed logging mechanism provides the best performance under a variety of write patterns, showing 8.6%, 14.2%, and 23.6% better performance compared to the previous undo, redo, and undo+redo approaches, respectively.