Hybrid hash index for NAND flash memory-based storage systems

Recently, NAND flash memory has become an alternative storage system for a storage device because of its rapid access speed, shock-resistant, small size, and lower power consumption. However, compared to the disk-based storage device, NAND flash memory has several hardware limitations such as asymmetric speed of read, write and erase operations and no in-place update. Therefore, a hash index structure, one of the popular disk-based index structures, may result in severe performance degradation if it is directly deployed on NAND flash memory. In this paper, we propose a new hash index structure that delays split operations which cause additional write and erase operations by using overflow buckets when bucket overflow occurs rather than immediate invocation of split operations. Also, we present a new overflow bucket maintenance policy that can reduce the number of additional read and write operations by adaptively handling the number of overflow buckets according to the ratio of update and delete records for each bucket. Finally, we show the superiority of the proposed index structure by comparing it to traditional extendible hash index through various experiments.