A Novel Method to Extend Flash Memory Lifetime in Flash-Based DBMS

Over the past decades, flash memory has been widely used in hand-held devices, such as PDA, digital camera, cell phone and USB stick. Moreover, as the capacity increases and the price drops gradually, flash memory is becoming the promising replacement of hard disk, even in the enterprise application. As a novel storage medium that is totally different from magnetic disk, flash memory enjoys faster access speed, smaller size, lighter weight, less noise and better shock resistance. However, flash memory suffers from erase-before-write and limited write-erase cycles on the other side, which means the abuse of write, especially small and random write, will wear a flash block out quickly. In this paper, we analyze the free space management in traditional DBMS and point out its disadvantage when used on flash device. Based on this, we propose a new solution involving free space management and buffer management, in which we replace the traditional free space management method employed in most disk-based DBMS, such as space map or free list, with the Append Only(AO) to avoid useless search and use a stand-alone write buffer to reduce the number of small writes to underlying flash device. Evaluation experiments based on four different trace files show that, in comparison with the traditional strategy, our solution reduces 74.5% of page writes in average, and accordingly succeed in extending the lifetime of flash device.