基于NVM的无日志哈希表

Logless Hash Table Based on NVM

新兴的非易失内存正逐步进入人们的视野。由于这类存储技术同时具备了低延迟、持久化、大容量和字节可寻址的特性,数据库系统可以运行在只有NVM的存储架构上。在这种环境下,一些新颖的无日志索引结构应运而生,并被期望在异常故障后能即时地恢复索引能力而无须重建索引。然而,在现有的计算机体系结构中,这些索引结构为了确保NVM上数据的一致性,需要进行大量的同步操作,从而严重影响了正常执行时的系统性能。基于NVM的无日志哈希表利用指针数据的原子修改确保数据结构的一致性。哈希表使用了一种优化的Rehash方法,既减少了正常工作时的同步操作,又确保了异常故障后的即时恢复能力。实验评估表明,相比于已有的持久化索引结构,无日志哈希表在大部分工作负荷下的吞吐率表现良好,而在恢复时间、NVM资源使用量和写磨损方面具备显著的优势。

Emerging non-volatile memory(NVM) is taking people’s attention.Due to the advantages of low latency,persistence,large capacity and byte- addressable,database system can run on the NVM-only storage architecture .In this configuration,some novel logless indexing structures come into being and are expected to recover indexing capability immediately after an system failure.However,under the current computer architecture,these structures need a large amount of synchronizations to ensure data consistency,which leads to a severe performance penalty.NVM-baesd logless hash table leverages the atomic update of the pointer data to ensure the consistency.An optimized rehash procedure was proposed to not only reduce the synchronizations during normal execution,but also ensure the instant recovery after system failures.Performance evaluation shows that,compared with existing persistent indexing structures,logless hash tables perform well under most workloads,and have significant advantages in terms of recovery time,NVM footprint,and write wear.