A Key-Value Store Based On SCM

Non-volatile memories(NVMs)are very promising technologies that would make some changes to the memory hierarchy of computer.Their abilities of byte addressability,low latency and persistence make them great alternatives to DRAM or disk.Some of them are also named as storage class memories(SCMs)because they are byte-addressable and can store data in replace of the disk.They would be attached to the memory bus and be accessed via load/store instructions,thus there is a good opportunity to design fast storage systems.The current popular key-value stores built for external memories,heavily rely on file systems to persist data,and cannot directly access to SCMs.Several key-value stores proposed for SCMs fail to provide data consistency by assuming that data in CPU caches or write buffers would be persisted automatically with the help of hardware.In this paper,we take advantage of both the abilities of SCMs and the characteristics of key-value workloads,to present a lightweight log-structured key-value store for SCMs named SCMKV.It exploits the log-structured technology to manage memory,implements a multilevel memory allocator to allocate memory fast,and maintains per-thread data logs to improve concurrency.Considering that the characteristics of key-value workloads,it provides a carefully estimated hash table to reduce the possibility of hash collisions and the number of resizing the hash table.It uses the cache-friendly array chains to resolve the hash collisions.Since the write latency of SCMs may be larger than DRAM,it puts the garbage collection's information on DRAM to avoid the write access to SCM.SCMKV has achieved 2.1 Mops with a single thread and achieved 5.4 Mops with four threads when we evaluate its writing ability with the uniform distributed small objects.