Competitive clustering of stochastic communication patterns on a ring

Chen Avin, Louis Cohen, Mahmoud Parham, Stefan Schmid

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


This paper studies a fundamental dynamic clustering problem. The input is an online sequence of pairwise communication requests between n nodes (e.g., tasks or virtual machines). Our goal is to minimize the communication cost by partitioning the communicating nodes into ℓ clusters (e.g., physical servers) of size k (e.g., number of virtual machine slots). We assume that if the communicating nodes are located in the same cluster, the communication request costs 0; if the nodes are located in different clusters, the request is served remotely using inter-cluster communication, at cost 1. Additionally, we can migrate: a node from one cluster to another at cost α≥ 1. We initiate the study of a stochastic problem variant where the communication pattern follows a fixed distribution, set by an adversary. Thus, the online algorithm needs to find a good tradeoff between benefitting from quickly moving to a seemingly good configuration (of low inter-cluster communication costs), and the risk of prematurely ending up in a configuration which later turns out to be bad, entailing high migration costs. Our main technical contribution is a deterministic online algorithm which is O(log n) -competitive with high probability (w.h.p.), for a specific but fundamental class of problems: namely on ring graphs. We also provide first insights in slightly more general models, where the adversary is not restricted to a fixed distribution or the ring.

Original languageEnglish
Pages (from-to)1369-1390
Number of pages22
JournalComputing (Vienna/New York)
Issue number9
StatePublished - 1 Sep 2019


  • Clustering
  • Migration
  • Online algorithms
  • Randomization
  • Repartition

ASJC Scopus subject areas

  • Software
  • Theoretical Computer Science
  • Numerical Analysis
  • Computer Science Applications
  • Computational Theory and Mathematics
  • Computational Mathematics


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