Abstract
We consider the randomized k-server problem, and give improved results for various metric spaces. In particular, we extend a recent result of Coté et al [15] for well-separated binary Hierarchically Separated Trees (HSTs) to well-separated d-ary HSTs for poly-logarithmic values of d. One application of this result is an \({\rm exp}(O(\sqrt{\log \log k \log n}))\)-competitive algorithm for k-server on n uniformly spaced points on a line. This substantially improves upon the prior guarantee of O( min (k,n 2/3) for this metric [16].
These results are based on obtaining a refined guarantee for the unfair metrical task systems problem on an HST. Prior to our work, such a guarantee was only known for the case of a uniform metric [5,7,18]. Our results are based on the primal-dual approach for online algorithms. Previous primal-dual approaches in the context of k-server and MTS [2,4,3] worked only for uniform or weighted star metrics, and the main technical contribution here is to extend many of these techniques to work directly on HSTs.
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Bansal, N., Buchbinder, N., Naor, J.(. (2010). Metrical Task Systems and the k-Server Problem on HSTs. In: Abramsky, S., Gavoille, C., Kirchner, C., Meyer auf der Heide, F., Spirakis, P.G. (eds) Automata, Languages and Programming. ICALP 2010. Lecture Notes in Computer Science, vol 6198. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-14165-2_25
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