Eliminating duplicate writes of logging via no-logging flash translation layer in SSDs

Abstract

With the development of high-density flash memory techniques, SSDs have achieved high performance and large capacity. Databases often use logging to ensure transactional atomicity of data updates. However, it introduces duplicate writes because of multi-versioning, which significantly weakens the performance and endurance of SSDs. This is also often considered as the main reason for slow response of databases. This paper proposes a novel flash translation layer (FTL) for SSDs, which we refer to as NoLgn-FTL, to reduce the overhead of logging-induced duplicate writes by exploiting the inherent multi-version feature of flash memories. Specifically, during a transaction, NoLgn-FTL retains the old data as valid and establishes the mapping between the new physical addresses and the old physical addresses. Thus, the database can easily roll back to the old-version data to maintain system consistency when a power failure occurs. To evaluate NoLgn-FTL, we implement it within FEMU and modify the SQLite database and the file system to make them compatible with the extended abstractions provided by NoLgn-FTL. Experimental results show that, in normal synchronization mode, NoLgn-FTL can reduce SSD writes by 20% and improve database performance by 15% on average.