Multi-Buffer Manager: Energy Efficient Buffer Manager for Databases on Flash Memory

Embedded devices such as personal digital assistants (PDAs), pocket PCs, palmtops, and handheld PCs are increasingly using flash memory for the permanent storage of databases. Databases achieve their fast data access speeds by using a memory manager which manages data pages in a memory buffer. The buffer manager uses a page replacement policy to evict pages when the memory buffer is full. An eviction of a dirty page will result in a write to flash memory. Unfortunately, writing to flash memory consumes a lot more energy than reading. Much of the previous work in page replacement policies has focused on reducing the number of page reads rather than writes. One of the few existing works to consider the effects of flash memory’s hardware constraints for database design is Lee et. al.’s [Lee and Moon 2007] In-page Logging (IPL) approach. They demonstrated IPL significantly outperforms traditional disk-based databases when running on flash memory. However, they do not consider the energy efficiency of their approach in terms of the behaviour of the page replacement policy. This paper addresses this issue by presenting the Multi-Buffer manager which is customized for flash databases that uses a logging-based approach for managing updates such as IPL. Extensive experiments show the page replacement policy used plays a pivotal role in the performance of the flash database system. In particular, our Multi-Buffer manager can reduce energy consumption by up to 40 % compared to the state-of-the-art clean first flash-based buffer replacement policy (CFLRU)