Abstract
We study an online job scheduling problem arising in networks with aggregated links. The goal is to schedule n jobs, divided into k disjoint chains, on m identical machines, without preemption, so that the jobs within each chain complete in the order of release times and the maximum flow time is minimized.
We present a deterministic online algorithm \(\mathsf{Block}\) with competitive ratio \(O(\sqrt{n/m})\) , and show a matching lower bound, even for randomized algorithms. The performance bound for \(\mathsf{Block}\) we derive in the paper is, in fact, more subtle than a standard competitive ratio bound, and it shows that in overload conditions (when many jobs are released in a short amount of time), \(\mathsf{Block}\) ’s performance is close to the optimum.
We also show how to compute an offline solution efficiently for k=1, and that minimizing the maximum flow time for k,m≥2 is \({ \mathcal {N}\mathcal {P}}\) -hard. As by-products of our method, we obtain two offline polynomial-time algorithms for minimizing makespan: an optimal algorithm for k=1, and a 2-approximation algorithm for any k.
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W. Jawor and M. Chrobak supported by NSF grants OISE-0340752 and CCR-0208856.
Work of C. Dürr conducted while being affiliated with the Laboratoire de Recherche en Informatique, Université Paris-Sud, 91405 Orsay. Supported by the CNRS/NSF grant 17171 and ANR Alpage.
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Jawor, W., Chrobak, M. & Dürr, C. Competitive Analysis of Scheduling Algorithms for Aggregated Links. Algorithmica 51, 367–386 (2008). https://doi.org/10.1007/s00453-007-9053-2
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DOI: https://doi.org/10.1007/s00453-007-9053-2