Fast transaction logging for smartphones

Mobile databases and key-value stores provide consistency and durability through write-ahead logging. The traditional logging scheme appends the log records to the end of the log file and flushes the records to durable storage using fsync(). Due to the large block size of the underlying file system and the Journaling of Journal anomaly, the logging latency becomes the main bottleneck of the mobile databases. Our experimental results indicate that the logging latency accounts for more than 90% of the overall insert latency on a Samsung Galaxy S4 smartphone. Moreover, we observe a significant write amplification (up to 122×) induced by the traditional logging scheme. In this paper we present xLog, a fast transaction logging service leveraging qNVRAM, a nearly non-volatile memory for mobile devices. From our experimental results, xLog logs up to 77× faster than the traditional logging scheme, and speeds up the LevelDB Put operation by up to 10.7×. Moreover, xLog drastically reduces the write amplification of the traditional logging scheme, from 122× to less than 1.6×.