Hint-based cooperative caching

This article presents the design, implementation, and measurement of a hint -based cooperative caching file system. Hints allow clients to make decisio ns based on local state, enabling a loosely coordinated system that is simp le to implement. The resulting performance is comparable to that of existin g tightly coordinated algorithms that use global state, but with less overh ead. Simulations show that the block access times of our system are as good as those of the existing algorithms, while reducing manager load by more t han a factor of seven, block lookup traffic by nearly a factor of two-third s, and replacement traffic a factor of five. To verify our simulation resul ts in a real system with real users, we implemented a prototype and measure d its performance for one week. Although the simulation and prototype envir onments were very different, the prototype system mirrored the simulation r esults by exhibiting reduced overhead and high hint accuracy. Furthermore, hint-based cooperative caching reduced the average block access time to alm ost half that of NFS.