FastDu: Efficient Directory Summaries Harvest by Tracking File System Changes

FastDu is a file system service that tracks file system changes by intercepting file system calls to maintain directory summaries, which play important roles in both storage administration and improvement of user experiences for some applications. In most circumstances, directory summaries are independently harvested by applications via traversing the file system hierarchy and calling stat () on every file in each directory. For large file systems, this brute-force traverse-based approach can take many hours to complete, even if only a small percentage of the files have changed. This paper describes FastDu, which uses a pre-built database to store harvested directory summaries, and tracks the file system changes by intercepting file system calls, so that new harvesting is restricted to the small subset of directories that contain modified files. Tests using FastDu show that this approach reduces the time needed to get a directory summary by one or two orders of magnitude with almost negligible penalty to application-aware file system performance.     

无柄醉鱼草与大叶醉鱼草的遗传多样性解析

无柄醉鱼草(Buddleja sessilifolia)是狭域分布的极小种群野生植物(Plant Species with Extremely Small Populations, PSESP),大叶醉鱼草(B.davidii)则是广布种,二者亲缘关系较近,且同为四倍体。通过比较濒危物种与近缘广布种的遗传多样性,可以了解濒危物种的演化历史,为制定保护策略提供理论依据。本研究通过简单重复序列(Simple Sequence Repeats, SSR)分子标记对无柄醉鱼草5个居群(126个个体)和大叶醉鱼草14个居群(206个个体)进行遗传多样性和遗传结构解析,并提出对无柄醉鱼草的保护建议。结果表明,无柄醉鱼草和大叶醉鱼草各居群的期望杂合度(He)平均值分别为0.606、0.775,Shannon′s多样性指数(I)平均值分别为1.162、1.729,两个物种均具有较高的遗传多样性,但广布种大叶醉鱼草遗传多样性水平高于狭域种无柄醉鱼草;无柄醉鱼草和大叶醉鱼草遗传分化系数(F_ST)分别为0.043和0.024,两个物种居群间遗传分化程度均较低。遗传结构分析结果表明,无柄...