In-memory write-ahead logging for mobile smart devices with NVRAM

In recent years, ensuring the reliability of databases in battery-powered mobile devices such as smartphones and tablets has gained in importance, since most mobile applications use a lightweight embedded database. Write-ahead logging (WAL) has been one of the representative techniques in embedded databases to ensure their reliability. However, this technique causes additional data write overhead. Besides, the file system provides its own reliability technique and this may therefore cause duplicate overhead. Both types of overhead lead to the performance degradation of mobile applications and have an adverse effect on the user experience. This paper proposes an efficient in-memory write-ahead logging (IMWAL) technique for the embedded databases of mobile devices adopting nonvolatile random access memory (NVRAM). When a write operation for the embedded database is invoked, IMWAL assures that the new data in a mobile application are all written to the NVRAM as a write-ahead data log. This data log is reused to update the embedded database file by remapping the memory address and therefore it reduces the additional writes. With IMWAL, write operations can resume even after crashes occur in the mobile devices and ensure the reliability of the embedded database with performance improvement. To evaluate the proposed technique, it is implemented on the in-memory file system of a real mobile platform. Its performance is evaluated against original WAL-on mode and WAL-off mode with various experiments, including various benchmarks and real mobile application workloads. The results show that IMWAL performs 14% faster than the original WAL technique for embedded databases in real mobile devices on average1.