License: Creative Commons Attribution 4.0 International license (CC BY 4.0)
When quoting this document, please refer to the following
DOI: 10.4230/LIPIcs.DISC.2021.1
URN: urn:nbn:de:0030-drops-148030
URL: http://dagstuhl.sunsite.rwth-aachen.de/volltexte/2021/14803/
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Haeupler, Bernhard

The Quest for Universally-Optimal Distributed Algorithms (Invited Talk)

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LIPIcs-DISC-2021-1.pdf (0.3 MB)

Abstract

Many distributed optimization algorithms achieve an existentially-optimal round complexity (of (Õ(√n + D)), i.e., there exists some pathological worst-case topology on which no algorithm can be faster. However, most networks of interest allow for exponentially faster algorithms. This motivates two questions:
- What network topology parameters determine the complexity of distributed optimization?
- Are there universally-optimal algorithms that are as fast as possible on every single topology?
This talk provides an overview over the freshly-completed 6-year program that resolves these 25-year-old open problems for a wide class of global network optimization problems including MST, (1+ε)-min cut, various approximate shortest path problems, sub-graph connectivity, etc. We provide several equivalent graph parameters that are tight universal lower bounds for the above problems, fully characterizing their inherent complexity. We also give the first universally-optimal algorithms approximately achieving this complexity on every topology.
The quest for universally-optimal distributed algorithms required novel techniques that also answer fundamental (open) questions in seemingly unrelated fields, such as, network information theory, approximation algorithms, (oblivious) packet routing, (algorithmic & topological) graph theory, and metric embeddings. Generally, the problems addressed in these fields explicitly or implicitly ask to jointly optimize ?_∞ & ?₁ parameters such as congestion & dilation, communication rate & delay, capacities & diameters of subnetworks, or the makespan of packet routings. In particular, results obtained on the way include the following firsts: (Congestion+Dilation)-Competitive Oblivious Routing, Network Coding Gaps for Completion-Times, Hop-Constrained Expanders & Expander Decompositions, Bi-Criteria (Online / Demand-Robust) Approximation Algorithms for many Diameter-Constrained Network Design Problems (e.g., (Group) Steiner Tree/Forest), Makespan-Competitive (Compact and Distributed) Routing Tables, and (Probabilistic) Tree Embeddings for Hop-Constrained Distances.

(Joint work with M. Ghaffari, G. Zuzic, D.E. Hershkowitz, D. Wajc, J. Li, H. Raecke, T. Izumi)

BibTeX - Entry

@InProceedings{haeupler:LIPIcs.DISC.2021.1,
  author =	{Haeupler, Bernhard},
  title =	{{The Quest for Universally-Optimal Distributed Algorithms}},
  booktitle =	{35th International Symposium on Distributed Computing (DISC 2021)},
  pages =	{1:1--1:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-210-5},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{209},
  editor =	{Gilbert, Seth},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/opus/volltexte/2021/14803},
  URN =		{urn:nbn:de:0030-drops-148030},
  doi =		{10.4230/LIPIcs.DISC.2021.1},
  annote =	{Keywords: Distributed algorithms}
}

Keywords: Distributed algorithms
Collection: 35th International Symposium on Distributed Computing (DISC 2021)
Issue Date: 2021
Date of publication: 04.10.2021

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