New algorithms for an ancient scheduling problem

  • Authors:
  • Yair Bartal;Amos Fiat;Howard Karloff;Rakesh Vohra

  • Affiliations:
  • Computer Science Department, School of Mathematics, Tel-Aviv University, Tel-Aviv 69978, Israel;Computer Science Department, School of Mathematics, Tel-Aviv University, Tel-Aviv 69978, Israel;Department of Computer Science, University of Chicago;Department of Management Science, Ohio State University

  • Venue:
  • STOC '92 Proceedings of the twenty-fourth annual ACM symposium on Theory of computing
  • Year:
  • 1992

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Abstract

We consider the on-line version of the original m-machine scheduling problem: given m machines and n positive real jobs, schedule the n jobs on the m machines so as to minimize the makespan, the completion time of the last job. In the on-line version, as soon as job j arrrives, it must be assigned immediately to one of the m machines.We present two main results. The first is a (2–&egr;)-competitive deterministic algorithm for all m. The competitive ratio of all previous algorithms approaches 2 as m→ ∞ . Indeed, the problem of improving the competitive ratio for large m had been open since 1966, when the first algorithm for this problem appeared.The second result is an optimal randomized algorithm for the case m = 2. To the best of our knowledge, our 4/3-competitive algorithm is the first specifically randomized algorithm for the original, m-machine, on-line scheduling problem.