A primal-dual randomized algorithm for weighted paging

Nikhil Bansal*, Niv Buchbinder, Joseph Naor

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


In the weighted paging problem there is a weight (cost) for fetching each page into the cache. We design a randomized O(log k)-competitive online algorithm for the weighted paging problem, where k is the cache size. This is the first randomized o(k)-competitive algorithm and its competitiveness matches the known lower bound on the problem. More generally, we design an O(log(k/(k-h + 1)))-competitive online algorithm for the version of the problem where, the online algorithm has cache size k and the offline algorithm has cache size h ≤ k. Weighted paging is a special case (weighted star metric) of the well known k-server problem for which it is a major open question whether randomization can be useful in obtaining sublinear competitive algorithms. Therefore, abstracting and extending the insights from paging is a key step in the resolution of the k-server problem. Our solution for the weighted paging problem is based on a two-step approach. In the first step we obtain an O(log k)-competitive fractional algorithm which is based on a novel online primal-dual approach. In the second step we obtain a randomized algorithm by rounding online the fractional solution to an actual distribution on integral cache solutions. We conclude with a randomized O(log N)-competitive algorithm, for the well studied Metrical Task System problem (MTS) on a metric defined by a weighted star on N leaves, improving upon a previous O(log2 N)-competitive algorithm of Blum et al. [9].

Original languageEnglish
Title of host publicationProceedings of the 48th Annual IEEE Symposium on Foundations of Computer Science, FOCS 2007
Number of pages11
StatePublished - 2007
Externally publishedYes
Event48th Annual Symposium on Foundations of Computer Science, FOCS 2007 - Providence, RI, United States
Duration: 20 Oct 200723 Oct 2007

Publication series

NameProceedings - Annual IEEE Symposium on Foundations of Computer Science, FOCS
ISSN (Print)0272-5428


Conference48th Annual Symposium on Foundations of Computer Science, FOCS 2007
Country/TerritoryUnited States
CityProvidence, RI


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