PC-OPT: Optimal Offline Prefetching and Caching for Parallel I/O Systems

  • Authors:
  • Mahesh Kallahalla;Peter J. Varman

  • Affiliations:
  • -;-

  • Venue:
  • IEEE Transactions on Computers
  • Year:
  • 2002

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Abstract

We address the problem of prefetching and caching in a parallel I/O system and present a new algorithm for parallel disk scheduling. Traditional buffer management algorithms that minimize the number of block misses are substantially suboptimal in a parallel I/O system where multiple I/Os can proceed simultaneously. We show that in the offline case, where a priori knowledge of all the requests is available, PC-OPT performs the minimum number of I/Os to service the given I/O requests. This is the first parallel I/O scheduling algorithm that is provably offline optimal in the parallel disk model.In the online case, we study the context of global L-block lookahead, which gives the buffer management algorithm a lookahead consisting of L distinct requests. We show that the competitive ratio of PC-OPT, with global L-blocklookahead, is \Theta (M - L + D), when L M, where the number of disks is D and buffer size is M.