The Design, Implementation, and Evaluation of a Predictive Caching File System

Conventional le systems suuer from high access latencies Ous90]. To complicate matters, emerging technologies such as wireless computing, telecommuting environments, read/write CD-ROM systems, and wide area le systems often exhibit higher latencies than conventional le systems. This paper describes the design, implementation, and evaluation of a predictive le caching approach. Predictive caching reduces le system latency by converting the le cache into a staging area for data about to be referenced as opposed to the conventional repository of recently accessed data. The system uses heuristic-based algorithms to predict and prefetch data without user or application intervention. A pruning algorithm keeps prefetching overhead in check. We show the expected performance gains for a variety of simulated environments. Simulations run on le traces show that prefetching can improve cache miss rates by as much as 70% and read times by as much as 52%. For certain common workloads (e.g., compilation), our algorithm achieves performance similar to that of an optimal prediction system. Our prototype SunOS implementation veriies the simulation results and shows read improvements of as much as 61% for real applications. Finally, our results show that prefetching can help small memory machines achieve the same performance as machines with twice as much memory.