Prefetching Over a Network: Early Experience With CTIP
Appears in SIGMETRICS Performance Evaluation Review, volume 25, number 3, (pp 29-36).
David Rochberg and Garth Gibson
School of Computer Science
Carnegie Mellon University
Pittsburgh, PA 15213
We discuss CTIP, an implementation of a network filesystem extension of the successful TIP informed prefetching and cache manage ment system. Using a modified version of TIP in NFS client machines (and unmodified NFS servers), CTIP takes advantage of application-supplied hints that disclose the application's future read accesses. CTIP uses these hints to aggressively prefetch file data from an NFS file server and to make better local cache replacement decisions. This prefetching hides disk latency and exposes storage parallelism. Preliminary measurements that show CTIP can reduce execution time by a ratio comparable to that obtained with local TIP over a suite of I/O-intensive hinting applications. (For four disks, the reduc tions in execution time range from 17% to 69%). If local TIP execu tion requires that data first be loaded from remote storage into a local scratch area, then CTIP execution is significantly faster than the aggregate time for loading the data and executing. Additionally, our measurements show that the benefit of CTIP for hinting applica tions improves in the face of competition from other clients for server resources. We conclude with an analysis of the remaining problems with using unmodified NFS servers.