Page-Differential Logging: An Efficient and DBMS-independent Approach for Storing Data into Flash Memory

摘要

Flash memory is widely used as the secondary storage in lightweight computingdevices due to its outstanding advantages over magnetic disks. Flash memory hasmany access characteristics different from those of magnetic disks, and how totake advantage of them is becoming an important research issue. There are twoexisting approaches to storing data into flash memory: page-based andlog-based. The former has good performance for read operations, but poorperformance for write operations. In contrast, the latter has good performancefor write operations when updates are light, but poor performance for readoperations. In this paper, we propose a new method of storing data, calledpage-differential logging, for flash-based storage systems that solves thedrawbacks of the two methods. The primary characteristics of our method are:(1) writing only the difference (which we define as the page-differential)between the original page in flash memory and the up-to-date page in memory;(2) computing and writing the page-differential only once at the time the pageneeds to be reflected into flash memory. The former contrasts with existingpage-based methods that write the whole page including both changed andunchanged parts of data or from log-based ones that keep track of the historyof all the changes in a page. Our method allows existing disk-based DBMSs to bereused as flash-based DBMSs just by modifying the flash memory driver, i.e., itis DBMS-independent. Experimental results show that the proposed methodimproves the I/O performance by 1.2 ~ 6.1 times over existing methods for theTPC-C data of approximately 1 Gbytes.