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Randomized Parallel Prefetching and Buffer Management

  • Mahesh Kallahalla
  • Peter J. Varman
Part of the Combinatorial Optimization book series (COOP, volume 5)

Abstract

There is increasing interest in the use of multiple-disk parallel I/O systems to alleviate the I/O bottleneck. Effective use of I/O parallelism requires careful coordination between data placement, prefetching and caching policies. We address the problems of I/O scheduling and buffer management in a parallel I/O system. Using the standard parallel disk model with D disks and a shared I/O buffer of M blocks, we study the performance of on-line algorithms that use bounded lookahead.

We first discuss algorithms for read-once reference strings. It is known (see [3]) that any deterministic prefetching algorithm with either global M-block n local lookahead, must perform a significantly larger number of I/Os than the optimal off-line algorithm. We discuss several prefetching schemes based on a randomized data placement, and present a simple prefetching algorithm that is shown to perform the minimum (up to constants) expected number of I/Os.

For general read-many reference strings, introduce the concept of write-back whereby blocks are relocated between disks during the course of the computation. We show that any on-line algorithm wilh bounded lookahead using deterministic write-back and buffer management policies must have a competitive ratio of Ω(D). We therefore present a randomized algorithm, RAND-WB, that uses a novel randomized write-back scheme. RAND-WB obtains a competitive ratio of \(\Theta \left( {\sqrt D } \right)\), which is the best achievable by any on-line algorithm with only global M-block lookahead.

Keywords

Competitive Ratio Data Block Buffer Space Buffer Management Single Disk 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Kluwer Academic Publishers 1999

Authors and Affiliations

  • Mahesh Kallahalla
    • 1
  • Peter J. Varman
    • 1
  1. 1.Department of Electrical and Computer EngineeringRice UniversityHoustonUSA

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