SoftWrAP: A lightweight framework for transactional support of storage class memory

In-memory computing is gaining popularity as a means of sidestepping the performance bottlenecks of block storage operations. However, the volatile nature of DRAM makes these systems vulnerable to system crashes, while the need to continuously refresh massive amounts of passive memoryresident data increases power consumption. Emerging storage-class memory (SCM) technologies combine fast DRAM-like cache-line access granularity with the persistence of storage devices like disks or SSDs, resulting in potential 10x-100x performance gains, and low passive power consumption. This unification of storage and memory into a single directly-accessible persistent tier raises significant reliability and pro-grammability challenges. In this paper, we present SoftWrAP, an open-source framework for Software based Write-Aside Persistence. SoftWrAP provides lightweight atomicity and durability for SCM storage transactions, while ensuring fast paths to data in processor caches, DRAM, and persistent memory tiers. We use our framework to evaluate both handcrafted SCM-based microbenchmarks as well as existing applications, specifically the STX B+Tree library and SQLite database, backed by emulated SCM. Our results show significant benefits of SoftWrAP over existing methods such as undo logging and shadow copying, and can match non-atomic durable writes to SCM, thereby gaining atomic consistency almost for free.