X-FTL: transactional FTL for SQLite databases

In the era of smartphones and mobile computing, many popular applications such as Facebook, twitter, Gmail, and even Angry birds game manage their data using SQLite. This is mainly due to the development productivity and solid transactional support. For transactional atomicity, however, SQLite relies on less sophisticated but costlier page-oriented journaling mechanisms. Hence, this is often cited as the main cause of tardy responses in mobile applications. Flash memory does not allow data to be updated in place, and the copy-on-write strategy is adopted by most flash storage devices. In this paper, we propose X-FTL, a transactional flash translation layer(FTL) for SQLite databases. By offloading the burden of guaranteeing the transactional atomicity from a host system to flash storage and by taking advantage of the copy-on-write strategy used in modern FTLs, X-FTL drastically improves the transactional throughput almost for free without resorting to costly journaling schemes. We have implemented X-FTL on an SSD development board called OpenSSD, and modified SQLite and ext4 file system minimally to make them compatible with the extended abstractions provided by X-FTL. We demonstrate the effectiveness of X-FTL using real and synthetic SQLite workloads for smartphone applications, TPC-C benchmark for OLTP databases, and FIO benchmark for file systems.