Integrating SSD Caching into Database Systems

Flash-based solid state storage devices (SSDs) are now becoming commonplace in server environments. In this paper, we consider the use of SSDs as a persistent second-tier cache for database systems. We argue that it is desirable to change the behavior of the database system’s buffer cache when a second-tier SSD cache is used, so that the buffer cache is aware of which pages are in the SSD cache. We propose such an SSD-aware buffer cache manager, called GD2L. An interesting side effect of SSD-aware buffer cache management is that the rate with which a page will be evicted or written from the buffer cache will change when that page is moved into or out of the second-tier SSD cache. We also propose a technique, called CAC, for managing the contents of the second-tier cache. CAC is aware that moving pages into or out of the SSD cache will change their physical read and write rates. It anticipates these changes when making decisions about which pages to cache at the second tier.