Flash as cache extension for online transactional workloads

Considering the current price gap between hard disk and flash memory SSD storages, for applications dealing with large-scale data, it will be economically more sensible to use flash memory drives to supplement disk drives rather than to replace them. This paper presents FaCE, which is a new low-overhead caching strategy that uses flash memory as an extension to the RAM buffer of database systems. FaCE aims at improving the transaction throughput as well as shortening the recovery time from a system failure. To achieve the goals, we propose two novel algorithms for flash cache management, namely multi-version FIFO replacement and group second chance. This was possible due to flash write optimization as well as disk access reduction obtained by the FaCE caching methods. In addition, FaCE takes advantage of the nonvolatility of flash memory to fully support database recovery by extending the scope of a persistent database to include the data pages stored in the flash cache. We have implemented FaCE in the PostgreSQL open-source database server and demonstrated its effectiveness for TPC-C benchmarks in comparison with existing caching methods such as Lazy Cleaning and Linux Bcache.