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

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 μ*-Tree which natively works on NAND flash memory, aiming at improving performance over B⁺-Tree. μ*-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, μ*-Tree has an adaptive page layout scheme which dynamically adjusts the page layout according to the workload characteristics on-the-fly. μ*-Tree also allows flash pages with different page layouts to coexist in the same tree. Our evaluation results with real workload traces show that μ*-Tree outperforms 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, μ*-Tree improves the overall performance by up to five times compared to B⁺-Tree with the same cache size.