Abstract
We continue the investigation initiated in [2] of the quality of service (QoS) that is achievable by semi-clairvoyant online scheduling algorithms, which are algorithms that only require approximate knowledge of the initial processing time of each job, on a single machine. In [2] it is shown that the obvious semi-clairvoyant generalization of the Shortest Processing Time is O(1)-competitive with respect to average stretch on a single machine. In [2] it was left as an open question whether it was possible for a semi-clairvoyant algorithm to be O(1)-competitive with respect to average flow time on one single machine. Here we settle this open question by giving a semi-clairvoyant algorithm that is O(1)-competitive with respect to average flow time on one single machine. We also show a semi-clairvoyant algorithm on parallel machines that achieves up to contant factors the best known competitive ratio for clairvoyant on-line algorithms. In some sense one might conclude from this that the QoS achievable by semi-clairvoyant algorithms is competitive with clairvoyant algorithms.
It is known that the clairvoyant algorithm SRPT is optimal with respect to average flow time and is 2-competitive with respect to average stretch. Thus it is possible for a clairvoyant algorithm to be simultaneously competitive in both average flow time and average stretch. In contrast we show that no semi-clairvoyant algorithm can be simultaneously O(1)-competitive with respect to average stretch and O(1)-competitive with respect to average flow time. Thus in this sense one might conclude that the QoS achievable by semi-clairvoyant algorithms is not competitive with clairvoyant algorithms.
This is a preview of subscription content, log in via an institution to check access.
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Preview
Unable to display preview. Download preview PDF.
References
Awerbuch, B., Azar, Y., Leonardi, S., Regev, O.: Minimizing the flow time without migration. In: ACM Symposim on Theory of Computing, pp. 198–205 (1999)
Bender, M., Muthukrishnan, S., Rajaraman, R.: Improved algorithms for stretch scheduling. In: ACM/SIAM Symposium on Discrete Algorithms, pp. 762–771 (2002)
Becchetti, L., Leonardi, S.: Non-Clairvoyant Scheduling to Minimize the Average Flow Time on Single and Parallel Machines. In: ACM Symposium on Theorey of Computing (2001)
Berman, P., Coulston, C.: Speed is more powerful than clairvoyance. Nordic Journal of Computing 6(2), 181–193 (1999)
Crovella, M., Frangioso, R., Harchol-Balter, M.: Connection Scheduling in Web Servers. In: Proceedings of the 1999 USENIX Symposium on Internet Technologies and Systems (USITS 1999) (October 1999)
Edmonds, J.: Scheduling in the dark. Theoretical Computer Science 235(1), 109–141 (2000)
Kalyanasundaram, B., Pruhs, K.: Speed is as powerful as clairvoyance. Journal of the ACM 47(4), 617–643 (2000)
Kalyanasundaram, B., Pruhs, K.: Minimizing flow time nonclairvoyantly. In: IEEE Symposium on Foundations of Computer Science (1997)
Leonardi, S.: A simpler proof of preemptive total flow time approximation on parallel machines. In: Bampis, E., Jansen, K., Kenyon, C. (eds.) Efficient Approximation and Online Algorithms. LNCS, vol. 3484, pp. 203–212. Springer, Heidelberg (2006) (to appear), http://www.dis.uniroma1.it/~leon/
Leonardi, S., Raz, D.: Approximating total flow time on parallel machines. In: ACM Symposium on Theory of Computing, pp. 110–119. El Paso, Texas (1997)
Motwani, R., Phillips, S., Torng, E.: Non-clairvoyant scheduling. Theoretical Computer Science 130, 17–47 (1994)
Muthukrishnan, S., Rajaraman, R., Shaheen, R., Gehrke, J.: Online scheduling to minimize average stretch. In: IEEE Symposium on Foundations of Compter Science, pp. 433–442 (1997)
Phillips, C., Stein, C., Torng, E., Wein, J.: Optimal time-critical scheduling via resource augmentation. Algorithmica 32, 163–200 (2002)
Author information
Authors and Affiliations
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2003 Springer-Verlag Berlin Heidelberg
About this paper
Cite this paper
Becchetti, L., Leonardi, S., Marchetti-Spaccamela, A., Pruhs, K. (2003). Semi-clairvoyant Scheduling. In: Di Battista, G., Zwick, U. (eds) Algorithms - ESA 2003. ESA 2003. Lecture Notes in Computer Science, vol 2832. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-39658-1_9
Download citation
DOI: https://doi.org/10.1007/978-3-540-39658-1_9
Publisher Name: Springer, Berlin, Heidelberg
Print ISBN: 978-3-540-20064-2
Online ISBN: 978-3-540-39658-1
eBook Packages: Springer Book Archive