34 Search Results for "Ferreira, Bernardo"


Volume

LIPIcs, Volume 125

22nd International Conference on Principles of Distributed Systems (OPODIS 2018)

OPODIS 2018, December 17-19, 2018, Hong Kong, China

Editors: Jiannong Cao, Faith Ellen, Luis Rodrigues, and Bernardo Ferreira

Document
Complete Volume
LIPIcs, Volume 125, OPODIS'18, Complete Volume

Authors: Jiannong Cao, Faith Ellen, Luis Rodrigues, and Bernardo Ferreira

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
LIPIcs, Volume 125, OPODIS'18, Complete Volume

Cite as

22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@Proceedings{cao_et_al:LIPIcs.OPODIS.2018,
  title =	{{LIPIcs, Volume 125, OPODIS'18, Complete Volume}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018},
  URN =		{urn:nbn:de:0030-drops-101742},
  doi =		{10.4230/LIPIcs.OPODIS.2018},
  annote =	{Keywords: Computer systems organization, Dependable and fault-tolerant systems and networks, Computing methodologies, Distributed algorithms, Networks, Mobile networks, Wireless access networks, Ad hoc networks, Software and its engineering, Distributed systems organizing principles,}
}
Document
Front Matter
Front Matter, Table of Contents, Preface, Conference Organization

Authors: Jiannong Cao, Faith Ellen, Luis Rodrigues, and Bernardo Ferreira

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
Front Matter, Table of Contents, Preface, Conference Organization

Cite as

22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, pp. 0:i-0:xx, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{cao_et_al:LIPIcs.OPODIS.2018.0,
  author =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  title =	{{Front Matter, Table of Contents, Preface, Conference Organization}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{0:i--0:xx},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.0},
  URN =		{urn:nbn:de:0030-drops-100607},
  doi =		{10.4230/LIPIcs.OPODIS.2018.0},
  annote =	{Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
Keynote
Complexity of Multi-Valued Register Simulations: A Retrospective (Keynote)

Authors: Jennifer L. Welch

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
I will provide a historical perspective on wait-free simulations of multi-bit shared registers using single-bit shared registers, starting with classical results from the last century and ending with an overview of the recent resurgence of interest in the topic. Particular emphasis will be placed on the space and step complexities of such simulations.

Cite as

Jennifer L. Welch. Complexity of Multi-Valued Register Simulations: A Retrospective (Keynote). In 22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, p. 1:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{welch:LIPIcs.OPODIS.2018.1,
  author =	{Welch, Jennifer L.},
  title =	{{Complexity of Multi-Valued Register Simulations: A Retrospective}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{1:1--1:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.1},
  URN =		{urn:nbn:de:0030-drops-100611},
  doi =		{10.4230/LIPIcs.OPODIS.2018.1},
  annote =	{Keywords: Distributed Systems}
}
Document
Keynote
Distributed Systems and Databases of the Globe Unite! The Cloud, the Edge and Blockchains (Keynote)

Authors: Amr El Abbadi

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
Significant paradigm shifts are occurring in Access patterns are widely dispersed and large scale analysis requires real-time responses. Many of the fundamental challenges have been studied and explored by both the distributed systems and the database communities for decades. However, the current changing and scalable setting often requires a rethinking of basic assumptions and premises. The rise of the cloud computing paradigm with its global reach has resulted in novel approaches to integrate traditional concepts in novel guises to solve fault-tolerance and scalability challenges. This is especially the case when users require real-time global access. Exploiting edge cloud resources becomes critical for improved performance, which requires a reevaluation of many paradigms, even for a traditional problem like caching. The need for transparency and accessibility has led to innovative ways for managing large scale replicated logs and ledgers, giving rise to blockchains and their many applications. In this talk we will be explore some of these new trends while emphasizing the novel challenges they raise from both distributed systems as well as database points of view. We will propose a unifying framework for traditional consensus and commitment protocols, and discuss novel protocols that exploit edge computing resources to enhance performance. We will highlight the advantages and discuss the limitations of blockchains. Our overall goal is to explore approaches that unite and exploit many of the significant efforts made in distributed systems and databases to address the novel and pressing needs of today's global computing infrastructure.

Cite as

Amr El Abbadi. Distributed Systems and Databases of the Globe Unite! The Cloud, the Edge and Blockchains (Keynote). In 22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, p. 2:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{abbadi:LIPIcs.OPODIS.2018.2,
  author =	{Abbadi, Amr El},
  title =	{{Distributed Systems and Databases of the Globe Unite! The Cloud, the Edge and Blockchains}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{2:1--2:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.2},
  URN =		{urn:nbn:de:0030-drops-100625},
  doi =		{10.4230/LIPIcs.OPODIS.2018.2},
  annote =	{Keywords: Consensus, Commitment, Cloud, Edge Computing, Blockchain}
}
Document
Keynote
How to Make Decisions (Optimally) (Keynote)

Authors: Siddhartha Sen

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
Distributed systems are constantly faced with difficult decisions to make, such as in scheduling, caching, and traffic routing, to name a few. In most of these scenarios, the optimal decision is unknown and depends heavily on context. How can a system designer know if they have deployed the best decision-making policy, or if a different policy would perform better? As a community, we have developed a few methodologies for answering this question, some of them offline (e.g., simulation, trace-driven modeling) and some of them online (e.g., A/B testing). Neither approach is satisfactory: the offline methods suffer from bias and rely heavily on domain knowledge; the online methods are costly and difficult to deploy. What system designers ideally seek is the ability to ask "what if" questions about a policy without ever deploying it, which is called counterfactual evaluation. In this talk, I will show how reinforcement learning and causal inference can be synthesized to counterfactually evaluate a distributed system. We will apply this methodology to infrastructure systems in Azure, and face fundamental challenges and opportunities along the way. This talk will serve as an introduction to reinforcement learning and the counterfactual way of thinking, which I hope will interest and inspire the OPODIS community. I will start by introducing reinforcement learning (RL) as the right framework for modeling decisions in a distributed system. In RL, an agent learns by interacting with its environment: i.e., making decisions and receiving feedback for them. This is a stark contrast to traditional (supervised) learning, where the correct answer, or "label", is known. Since an RL agent does not know the correct answer, it must constantly explore its world by randomizing some of its decisions. Now it turns out that this randomization, if used correctly, can give us a special superpower: the ability to evaluate policies that have never been deployed. As magical as this may sound, we can use statistics to show that this evaluation is indeed correct. Unfortunately, applying this methodology to distributed systems is far from straightforward. Systems are complex, stateful amalgamations of components that navigate large decision spaces. We will need to wear both an RL hat and a systems hat to address these challenges. On the other hand, systems also present exciting opportunities. Many systems already use randomization in their decisions, e.g., to distribute data or work over replicas, or to manage resource contention. Sometimes, a conservative decision can implicitly yield feedback for other decisions: for example, when waiting for a timeout to expire, we automatically get feedback for what would have happened if we waited for any shorter amount of time. I will show how we can harvest this randomness and implicit feedback to achieve more effective counterfactual evaluation. We will apply all of the above ideas to two production infrastructure systems in Azure: a machine health monitor that decides when to reboot unresponsive machines, and a geo-distributed edge proxy that chooses the TCP configuration of each proxy machine. In both cases, we are able to counterfactually evaluate arbitrary policies with estimates that match the ground truth. Production environments raise interesting constraints and challenges, some of which are preventing us from scaling up our methodology. I will describe a possible path forward, and invite others in the community to contemplate these problems as well.

Cite as

Siddhartha Sen. How to Make Decisions (Optimally) (Keynote). In 22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, p. 3:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{sen:LIPIcs.OPODIS.2018.3,
  author =	{Sen, Siddhartha},
  title =	{{How to Make Decisions (Optimally)}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{3:1--3:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.3},
  URN =		{urn:nbn:de:0030-drops-100638},
  doi =		{10.4230/LIPIcs.OPODIS.2018.3},
  annote =	{Keywords: reinforcement learning, distributed systems, counterfactual evaluation}
}
Document
Sparse Matrix Multiplication and Triangle Listing in the Congested Clique Model

Authors: Keren Censor-Hillel, Dean Leitersdorf, and Elia Turner

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
We show how to multiply two n x n matrices S and T over semirings in the Congested Clique model, where n nodes communicate in a fully connected synchronous network using O(log{n})-bit messages, within O(nz(S)^{1/3} nz(T)^{1/3}/n + 1) rounds of communication, where nz(S) and nz(T) denote the number of non-zero elements in S and T, respectively. By leveraging the sparsity of the input matrices, our algorithm greatly reduces communication costs compared with general multiplication algorithms [Censor-Hillel et al., PODC 2015], and thus improves upon the state-of-the-art for matrices with o(n^2) non-zero elements. Moreover, our algorithm exhibits the additional strength of surpassing previous solutions also in the case where only one of the two matrices is such. Particularly, this allows to efficiently raise a sparse matrix to a power greater than 2. As applications, we show how to speed up the computation on non-dense graphs of 4-cycle counting and all-pairs-shortest-paths. Our algorithmic contribution is a new deterministic method of restructuring the input matrices in a sparsity-aware manner, which assigns each node with element-wise multiplication tasks that are not necessarily consecutive but guarantee a balanced element distribution, providing for communication-efficient multiplication. Moreover, this new deterministic method for restructuring matrices may be used to restructure the adjacency matrix of input graphs, enabling faster deterministic solutions for graph related problems. As an example, we present a new sparsity aware, deterministic algorithm which solves the triangle listing problem in O(m/n^{5/3} + 1) rounds, a complexity that was previously obtained by a randomized algorithm [Pandurangan et al., SPAA 2018], and that matches the known lower bound of Omega~(n^{1/3}) when m=n^2 of [Izumi and Le Gall, PODC 2017, Pandurangan et al., SPAA 2018]. Naturally, our triangle listing algorithm also implies triangle counting within the same complexity of O(m/n^{5/3} + 1) rounds, which is (possibly more than) a cubic improvement over the previously known deterministic O(m^2/n^3)-round algorithm [Dolev et al., DISC 2012].

Cite as

Keren Censor-Hillel, Dean Leitersdorf, and Elia Turner. Sparse Matrix Multiplication and Triangle Listing in the Congested Clique Model. In 22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, pp. 4:1-4:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{censorhillel_et_al:LIPIcs.OPODIS.2018.4,
  author =	{Censor-Hillel, Keren and Leitersdorf, Dean and Turner, Elia},
  title =	{{Sparse Matrix Multiplication and Triangle Listing in the Congested Clique Model}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{4:1--4:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.4},
  URN =		{urn:nbn:de:0030-drops-100645},
  doi =		{10.4230/LIPIcs.OPODIS.2018.4},
  annote =	{Keywords: congested clique, matrix multiplication, triangle listing}
}
Document
Large-Scale Distributed Algorithms for Facility Location with Outliers

Authors: Tanmay Inamdar, Shreyas Pai, and Sriram V. Pemmaraju

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
This paper presents fast, distributed, O(1)-approximation algorithms for metric facility location problems with outliers in the Congested Clique model, Massively Parallel Computation (MPC) model, and in the k-machine model. The paper considers Robust Facility Location and Facility Location with Penalties, two versions of the facility location problem with outliers proposed by Charikar et al. (SODA 2001). The paper also considers two alternatives for specifying the input: the input metric can be provided explicitly (as an n x n matrix distributed among the machines) or implicitly as the shortest path metric of a given edge-weighted graph. The results in the paper are: - Implicit metric: For both problems, O(1)-approximation algorithms running in O(poly(log n)) rounds in the Congested Clique and the MPC model and O(1)-approximation algorithms running in O~(n/k) rounds in the k-machine model. - Explicit metric: For both problems, O(1)-approximation algorithms running in O(log log log n) rounds in the Congested Clique and the MPC model and O(1)-approximation algorithms running in O~(n/k) rounds in the k-machine model. Our main contribution is to show the existence of Mettu-Plaxton-style O(1)-approximation algorithms for both Facility Location with outlier problems. As shown in our previous work (Berns et al., ICALP 2012, Bandyapadhyay et al., ICDCN 2018) Mettu-Plaxton style algorithms are more easily amenable to being implemented efficiently in distributed and large-scale models of computation.

Cite as

Tanmay Inamdar, Shreyas Pai, and Sriram V. Pemmaraju. Large-Scale Distributed Algorithms for Facility Location with Outliers. In 22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, pp. 5:1-5:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{inamdar_et_al:LIPIcs.OPODIS.2018.5,
  author =	{Inamdar, Tanmay and Pai, Shreyas and Pemmaraju, Sriram V.},
  title =	{{Large-Scale Distributed Algorithms for Facility Location with Outliers}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{5:1--5:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.5},
  URN =		{urn:nbn:de:0030-drops-100650},
  doi =		{10.4230/LIPIcs.OPODIS.2018.5},
  annote =	{Keywords: Distributed Algorithms, Clustering with Outliers, Metric Facility Location, Massively Parallel Computation, k-machine model, Congested Clique}
}
Document
Equilibria of Games in Networks for Local Tasks

Authors: Simon Collet, Pierre Fraigniaud, and Paolo Penna

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
Distributed tasks such as constructing a maximal independent set (MIS) in a network, or properly coloring the nodes or the edges of a network with reasonably few colors, are known to admit efficient distributed randomized algorithms. Those algorithms essentially proceed according to some simple generic rules, by letting each node choosing a temptative value at random, and checking whether this choice is consistent with the choices of the nodes in its vicinity. If this is the case, then the node outputs the chosen value, else it repeats the same process. Although such algorithms are, with high probability, running in a polylogarithmic number of rounds, they are not robust against actions performed by rational but selfish nodes. Indeed, such nodes may prefer specific individual outputs over others, e.g., because the formers suit better with some individual constraints. For instance, a node may prefer not being placed in a MIS as it is not willing to serve as a relay node. Similarly, a node may prefer not being assigned some radio frequencies (i.e., colors) as these frequencies would interfere with other devices running at that node. In this paper, we show that the probability distribution governing the choices of the output values in the generic algorithm can be tuned such that no nodes will rationally deviate from this distribution. More formally, and more generally, we prove that the large class of so-called LCL tasks, including MIS and coloring, admit simple "Luby's style" algorithms where the probability distribution governing the individual choices of the output values forms a Nash equilibrium. In fact, we establish the existence of a stronger form of equilibria, called symmetric trembling-hand perfect equilibria for those games.

Cite as

Simon Collet, Pierre Fraigniaud, and Paolo Penna. Equilibria of Games in Networks for Local Tasks. In 22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, pp. 6:1-6:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{collet_et_al:LIPIcs.OPODIS.2018.6,
  author =	{Collet, Simon and Fraigniaud, Pierre and Penna, Paolo},
  title =	{{Equilibria of Games in Networks for Local Tasks}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{6:1--6:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.6},
  URN =		{urn:nbn:de:0030-drops-100668},
  doi =		{10.4230/LIPIcs.OPODIS.2018.6},
  annote =	{Keywords: Local distributed computing, Locally checkable labelings}
}
Document
The Sparsest Additive Spanner via Multiple Weighted BFS Trees

Authors: Keren Censor-Hillel, Ami Paz, and Noam Ravid

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
Spanners are fundamental graph structures that sparsify graphs at the cost of small stretch. In particular, in recent years, many sequential algorithms constructing additive all-pairs spanners were designed, providing very sparse small-stretch subgraphs. Remarkably, it was then shown that the known (+6)-spanner constructions are essentially the sparsest possible, that is, larger additive stretch cannot guarantee a sparser spanner, which brought the stretch-sparsity trade-off to its limit. Distributed constructions of spanners are also abundant. However, for additive spanners, while there were algorithms constructing (+2) and (+4)-all-pairs spanners, the sparsest case of (+6)-spanners remained elusive. We remedy this by designing a new sequential algorithm for constructing a (+6)-spanner with the essentially-optimal sparsity of O~(n^{4/3}) edges. We then show a distributed implementation of our algorithm, answering an open problem in [Keren Censor{-}Hillel et al., 2016]. A main ingredient in our distributed algorithm is an efficient construction of multiple weighted BFS trees. A weighted BFS tree is a BFS tree in a weighted graph, that consists of the lightest among all shortest paths from the root to each node. We present a distributed algorithm in the CONGEST model, that constructs multiple weighted BFS trees in |S|+D-1 rounds, where S is the set of sources and D is the diameter of the network graph.

Cite as

Keren Censor-Hillel, Ami Paz, and Noam Ravid. The Sparsest Additive Spanner via Multiple Weighted BFS Trees. In 22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, pp. 7:1-7:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{censorhillel_et_al:LIPIcs.OPODIS.2018.7,
  author =	{Censor-Hillel, Keren and Paz, Ami and Ravid, Noam},
  title =	{{The Sparsest Additive Spanner via Multiple Weighted BFS Trees}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{7:1--7:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.7},
  URN =		{urn:nbn:de:0030-drops-100676},
  doi =		{10.4230/LIPIcs.OPODIS.2018.7},
  annote =	{Keywords: Distributed graph algorithms, congest model, weighted BFS trees, additive spanners}
}
Document
The Amortized Analysis of a Non-blocking Chromatic Tree

Authors: Jeremy Ko

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
A non-blocking chromatic tree is a type of balanced binary search tree where multiple processes can concurrently perform search and update operations. We prove that a certain implementation has amortized cost O(dot{c} + log n) for each operation, where dot{c} is the maximum number of concurrent operations at any point during the execution and n is the maximum number of keys in the tree during the operation. This amortized analysis presents new challenges compared to existing analyses of other non-blocking data structures.

Cite as

Jeremy Ko. The Amortized Analysis of a Non-blocking Chromatic Tree. In 22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, pp. 8:1-8:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{ko:LIPIcs.OPODIS.2018.8,
  author =	{Ko, Jeremy},
  title =	{{The Amortized Analysis of a Non-blocking Chromatic Tree}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{8:1--8:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.8},
  URN =		{urn:nbn:de:0030-drops-100688},
  doi =		{10.4230/LIPIcs.OPODIS.2018.8},
  annote =	{Keywords: amortized analysis, non-blocking, lock-free, balanced binary search trees}
}
Document
Lock-Free Search Data Structures: Throughput Modeling with Poisson Processes

Authors: Aras Atalar, Paul Renaud-Goud, and Philippas Tsigas

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
This paper considers the modeling and the analysis of the performance of lock-free concurrent search data structures. Our analysis considers such lock-free data structures that are utilized through a sequence of operations which are generated with a memoryless and stationary access pattern. Our main contribution is a new way of analyzing lock-free concurrent search data structures: our execution model matches with the behavior that we observe in practice and achieves good throughput predictions. Search data structures are formed of basic blocks, usually referred to as nodes, which can be accessed by two kinds of events, characterized by their latencies; (i) CAS events originated as a result of modifications of the search data structure (ii) Read events that occur during traversals. An operation triggers a set of events, and the running time of an operation is computed as the sum of the latencies of these events. We identify the factors that impact the latency of such events on a multi-core shared memory system. The main challenge (though not the only one) is that the latency of each event mainly depends on the state of the caches at the time when it is triggered, and the state of caches is changing due to events that are triggered by the operations of any thread in the system. Accordingly, the latency of an event is determined by the ordering of the events on the timeline. Search data structures are usually designed to accommodate a large number of nodes, which makes the occurrence of an event on a given node rare at any given time. In this context, we model the events on each node as Poisson processes from which we can extract the frequency and probabilistic ordering of events that are used to estimate the expected latency of an operation, and in turn the throughput. We have validated our analysis on several fundamental lock-free search data structures such as linked lists, hash tables, skip lists and binary trees.

Cite as

Aras Atalar, Paul Renaud-Goud, and Philippas Tsigas. Lock-Free Search Data Structures: Throughput Modeling with Poisson Processes. In 22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, pp. 9:1-9:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{atalar_et_al:LIPIcs.OPODIS.2018.9,
  author =	{Atalar, Aras and Renaud-Goud, Paul and Tsigas, Philippas},
  title =	{{Lock-Free Search Data Structures: Throughput Modeling with Poisson Processes}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{9:1--9:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.9},
  URN =		{urn:nbn:de:0030-drops-100698},
  doi =		{10.4230/LIPIcs.OPODIS.2018.9},
  annote =	{Keywords: Lock-free, Search Data Structures, Performance, Modeling, Analysis}
}
Document
Concurrent Robin Hood Hashing

Authors: Robert Kelly, Barak A. Pearlmutter, and Phil Maguire

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
In this paper we examine the issues involved in adding concurrency to the Robin Hood hash table algorithm. We present a non-blocking obstruction-free K-CAS Robin Hood algorithm which requires only a single word compare-and-swap primitive, thus making it highly portable. The implementation maintains the attractive properties of the original Robin Hood structure, such as a low expected probe length, capability to operate effectively under a high load factor and good cache locality, all of which are essential for high performance on modern computer architectures. We compare our data-structures to various other lock-free and concurrent algorithms, as well as a simple hardware transactional variant, and show that our implementation performs better across a number of contexts.

Cite as

Robert Kelly, Barak A. Pearlmutter, and Phil Maguire. Concurrent Robin Hood Hashing. In 22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, pp. 10:1-10:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{kelly_et_al:LIPIcs.OPODIS.2018.10,
  author =	{Kelly, Robert and Pearlmutter, Barak A. and Maguire, Phil},
  title =	{{Concurrent Robin Hood Hashing}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{10:1--10:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.10},
  URN =		{urn:nbn:de:0030-drops-100701},
  doi =		{10.4230/LIPIcs.OPODIS.2018.10},
  annote =	{Keywords: concurrency, Robin Hood Hashing, data-structures, hash tables, non-blocking}
}
Document
Parallel Combining: Benefits of Explicit Synchronization

Authors: Vitaly Aksenov, Petr Kuznetsov, and Anatoly Shalyto

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
A parallel batched data structure is designed to process synchronized batches of operations on the data structure using a parallel program. In this paper, we propose parallel combining, a technique that implements a concurrent data structure from a parallel batched one. The idea is that we explicitly synchronize concurrent operations into batches: one of the processes becomes a combiner which collects concurrent requests and initiates a parallel batched algorithm involving the owners (clients) of the collected requests. Intuitively, the cost of synchronizing the concurrent calls can be compensated by running the parallel batched algorithm. We validate the intuition via two applications. First, we use parallel combining to design a concurrent data structure optimized for read-dominated workloads, taking a dynamic graph data structure as an example. Second, we use a novel parallel batched priority queue to build a concurrent one. In both cases, we obtain performance gains with respect to the state-of-the-art algorithms.

Cite as

Vitaly Aksenov, Petr Kuznetsov, and Anatoly Shalyto. Parallel Combining: Benefits of Explicit Synchronization. In 22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, pp. 11:1-11:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{aksenov_et_al:LIPIcs.OPODIS.2018.11,
  author =	{Aksenov, Vitaly and Kuznetsov, Petr and Shalyto, Anatoly},
  title =	{{Parallel Combining: Benefits of Explicit Synchronization}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{11:1--11:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.11},
  URN =		{urn:nbn:de:0030-drops-100713},
  doi =		{10.4230/LIPIcs.OPODIS.2018.11},
  annote =	{Keywords: concurrent data structure, parallel batched data structure, combining}
}
Document
Specification and Implementation of Replicated List: The Jupiter Protocol Revisited

Authors: Hengfeng Wei, Yu Huang, and Jian Lu

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)


Abstract
The replicated list object is frequently used to model the core functionality of replicated collaborative text editing systems. Since 1989, the convergence property has been a common specification of a replicated list object. Recently, Attiya et al. proposed the strong/weak list specification and conjectured that the well-known Jupiter protocol satisfies the weak list specification. The major obstacle to proving this conjecture is the mismatch between the global property on all replica states prescribed by the specification and the local view each replica maintains in Jupiter using data structures like 1D buffer or 2D state space. To address this issue, we propose CJupiter (Compact Jupiter) based on a novel data structure called n-ary ordered state space for a replicated client/server system with n clients. At a high level, CJupiter maintains only a single n-ary ordered state space which encompasses exactly all states of each replica. We prove that CJupiter and Jupiter are equivalent and that CJupiter satisfies the weak list specification, thus solving the conjecture above.

Cite as

Hengfeng Wei, Yu Huang, and Jian Lu. Specification and Implementation of Replicated List: The Jupiter Protocol Revisited. In 22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, pp. 12:1-12:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{wei_et_al:LIPIcs.OPODIS.2018.12,
  author =	{Wei, Hengfeng and Huang, Yu and Lu, Jian},
  title =	{{Specification and Implementation of Replicated List: The Jupiter Protocol Revisited}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{12:1--12:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.12},
  URN =		{urn:nbn:de:0030-drops-100720},
  doi =		{10.4230/LIPIcs.OPODIS.2018.12},
  annote =	{Keywords: Collaborative text editing systems, Replicated list, Concurrency control, Strong/weak list specification, Operational transformation, Jupiter protocol}
}
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