μ*-Tree: An Ordered Index Structure for NAND Flash Memory with Adaptive Page Layout Scheme

摘要

As NAND flash memory is gaining popularity as a storage medium for mobile embedded devices, many flash-aware file systems, flash-aware DBMSes, and flash translation layers (FTLs) require an flash-efficient index structure. This paper proposes a novel index structure called $(mu^{ast })$-Tree which natively works on NAND flash memory, aiming at improving performance over $({rm B}^{+})$-Tree. $(mu^{ast })$--Tree stores all the nodes along the path from the root to the leaf into a single flash memory page in order to minimize the number of flash write operation when a node is updated. Furthermore, $(mu^{ast })$-Tree has an adaptive page layout scheme which dynamically adjusts the page layout according to the workload characteristics on-the-fly. $(mu^{ast })$-Tree also allows flash pages with different page layouts to coexist in the same tree. Our evaluation results with real workload traces show that $(mu^{ast })$-Tree outperforms $({rm B}^{+})$-Tree by up to 55 percent in terms of the time needed for flash operations. With a small in-memory cache of 32 KB, $(mu^{ast })$-Tree improves the overall performance by up to five times compared to $({rm B}^{+})$-Tree with the same cache size.