Volume
LIPIcs, Volume 153
23rd International Conference on Principles of Distributed Systems (OPODIS 2019)
Publication Details
- published at: 2020-02-11
- Publisher: Schloss Dagstuhl – Leibniz-Zentrum für Informatik
- ISBN: 978-3-95977-133-7
- DBLP: db/conf/opodis/opodis2019
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Document
Complete Volume
LIPIcs, Vol. 153, OPODIS 2019, Complete Volume
Abstract
LIPIcs, Vol. 153, OPODIS 2019, Complete Volume
Cite as
23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 1-564, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@Proceedings{felber_et_al:LIPIcs.OPODIS.2019,
title = {{LIPIcs, Vol. 153, OPODIS 2019, Complete Volume}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {1--564},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019},
URN = {urn:nbn:de:0030-drops-119510},
doi = {10.4230/LIPIcs.OPODIS.2019},
annote = {Keywords: LIPIcs, Vol. 153, OPODIS 2019, Complete Volume}
}
Document
Front Matter
Front Matter, Table of Contents, Preface, Conference Organization
Abstract
Front Matter, Table of Contents, Preface, Conference Organization
Cite as
23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 0:i-0:xxii, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{felber_et_al:LIPIcs.OPODIS.2019.0,
author = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
title = {{Front Matter, Table of Contents, Preface, Conference Organization}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {0:i--0:xxii},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.0},
URN = {urn:nbn:de:0030-drops-117869},
doi = {10.4230/LIPIcs.OPODIS.2019.0},
annote = {Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
Keynote Abstract
Demystifying Bitcoin (Keynote Abstract)
Abstract
This talk will explain the bitcoin algorithm from the distributed computing perspective, precisely define the underlying double-payment problem, and present a much simpler alternative to solve the problem without relying on consensus and consuming so much energy.
Rachid Guerraoui is professor in Computer Science at EPFL where he leads the Distributed Computing Laboratory. He worked in the past with École des Mines de Paris, CEA Saclay, HP Labs in Palo Alto and MIT. He has been elected ACM Fellow and Professor of the College de France. He was awarded a Senior ERC Grant and a Google Focused Award.
Cite as
Rachid Guerraoui. Demystifying Bitcoin (Keynote Abstract). In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, p. 1:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{guerraoui:LIPIcs.OPODIS.2019.1,
author = {Guerraoui, Rachid},
title = {{Demystifying Bitcoin}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {1:1--1:1},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.1},
URN = {urn:nbn:de:0030-drops-117870},
doi = {10.4230/LIPIcs.OPODIS.2019.1},
annote = {Keywords: Bitcoin, Payment systems}
}
Document
Keynote Abstract
Distributed Optimization And Approximation: How Difficult Can It Be? (Keynote Abstract)
Abstract
We know that exact distributed algorithms for optimization problems cannot be fast. To overcome these barriers, very efficient approximation algorithms have been designed in various distributed settings. But for very small approximation factors, a mystery remains: Why do we not have fast distributed algorithms for very small approximations factors in bandwidth restricted settings?
This talk will overview the state-of-the-art of distributed optimization and approximation algorithms and discuss the major challenges in determining the complexity of small approximations.
Cite as
Keren Censor-Hillel. Distributed Optimization And Approximation: How Difficult Can It Be? (Keynote Abstract). In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, p. 2:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{censorhillel:LIPIcs.OPODIS.2019.2,
author = {Censor-Hillel, Keren},
title = {{Distributed Optimization And Approximation: How Difficult Can It Be?}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {2:1--2:1},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.2},
URN = {urn:nbn:de:0030-drops-117886},
doi = {10.4230/LIPIcs.OPODIS.2019.2},
annote = {Keywords: Distributed graph algorithms, Optimization and approximations}
}
Document
Keynote Abstract
Snap ML - Accelerated Machine Learning for Big Data (Keynote Abstract)
Abstract
Snap Machine Learning (Snap ML) is a new software library for training popular machine learning models, characterized by very high performance, scalability to TB-scale datasets and high resource efficiency. It continuously evolves and currently supports generalized linear models, decision trees, random forests and gradient boosting machines. Snap ML has been built to address the needs of business applications, which often have to deal with high-volume data, react fast to changing environments, and use resources efficiently to drive down cost. The high efficiency of Snap ML, in particular in dealing with big data, comes from innovations in distributed optimization, among other things. This talk will review the principles of the Snap ML library, explain how it achieves high speed and scalability, and present several cases of business workloads that demonstrate the benefits offered by Snap ML.
Haris Pozidis manages the Cloud Storage and Analytics group at IBM Research in Zurich, Switzerland. He was with Philips Research, Eindhoven, The Netherlands, before joining IBM. He has worked on read channel design for DVD and Blu-ray Disc at Philips, and played a key role in developing the first scanning probe-based data storage system at IBM, the “Millipede”. His current focus is on the development of Flash memory controllers for all-flash arrays, on phase change memory technology and system solutions, and on accelerated software libraries for machine learning. He holds over 120 US patents, has co-authored more than 120 publications, is an IBM Principal Research Scientist and Master Inventor, and a Senior Member of the IEEE.
Cite as
Haris Pozidis. Snap ML - Accelerated Machine Learning for Big Data (Keynote Abstract). In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, p. 3:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{pozidis:LIPIcs.OPODIS.2019.3,
author = {Pozidis, Haris},
title = {{Snap ML - Accelerated Machine Learning for Big Data}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {3:1--3:1},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.3},
URN = {urn:nbn:de:0030-drops-117899},
doi = {10.4230/LIPIcs.OPODIS.2019.3},
annote = {Keywords: Machine Learning, Big Data}
}
Document
FairLedger: A Fair Blockchain Protocol for Financial Institutions
Abstract
Financial institutions nowadays are looking into technologies for permissioned blockchains. A major effort in this direction is Hyperledger, an open source project hosted by the Linux Foundation and backed by a consortium of over a hundred companies. A key component in permissioned blockchain protocols is a byzantine fault tolerant (BFT) consensus engine that orders transactions. However, currently available BFT solutions in Hyperledger (as well as in the literature at large) are inadequate for financial settings; they are not designed to ensure fairness or to tolerate the selfish behavior that inevitably arises when financial institutions strive to maximize their own profit.
We present FairLedger, a permissioned BFT blockchain protocol, which is fair, deigned to deal with rational behavior, and, no less important, easy to understand and implement. Our secret sauce is a new communication abstraction called detectable all-to-all (DA2A), which allows us to detect players (byzantine or rational) that deviate from the protocol and punish them. We implement FairLedger in the Hyperledger open source project using the Iroha framework - one of the biggest projects therein. To evaluate FairLegder’s performance, we also implement it in the PBFT framework and compare the two protocols. Our results show that in failure-free scenarios in wide-area settings, FairLedger achieves better throughput than both Iroha’s implementation and PBFT.
Cite as
Kfir Lev-Ari, Alexander Spiegelman, Idit Keidar, and Dahlia Malkhi. FairLedger: A Fair Blockchain Protocol for Financial Institutions. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 4:1-4:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{levari_et_al:LIPIcs.OPODIS.2019.4,
author = {Lev-Ari, Kfir and Spiegelman, Alexander and Keidar, Idit and Malkhi, Dahlia},
title = {{FairLedger: A Fair Blockchain Protocol for Financial Institutions}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {4:1--4:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.4},
URN = {urn:nbn:de:0030-drops-117904},
doi = {10.4230/LIPIcs.OPODIS.2019.4},
annote = {Keywords: Blockchain, Fairness, Byzantine fault tolerance, Rational players, Equilibrium}
}
Document
Deconstructing Stellar Consensus
Abstract
Some of the recent blockchain proposals, such as Stellar and Ripple, allow for open membership while using quorum-like structures typical for classical Byzantine consensus with closed membership. This is achieved by constructing quorums in a decentralised way: each participant independently chooses whom to trust, and quorums arise from these individual decisions. Unfortunately, the consensus protocols underlying such blockchains are poorly understood, and their correctness has not been rigorously investigated. In this paper we rigorously prove correct the Stellar Consensus Protocol (SCP), with our proof giving insights into the protocol structure and its use of lower-level abstractions. To this end, we first propose an abstract version of SCP that uses as a black box Stellar’s federated voting primitive (analogous to reliable Byzantine broadcast), previously investigated by García-Pérez and Gotsman [Álvaro García-Pérez and Alexey Gotsman, 2018]. The abstract consensus protocol highlights a modular structure in Stellar and can be proved correct by reusing the previous results on federated voting. However, it is unsuited for realistic implementations, since its processes maintain infinite state. We thus establish a refinement between the abstract protocol and the concrete SCP that uses only finite state, thereby carrying over the result about the correctness of former to the latter. Our results help establish the theoretical foundations of decentralised blockchains like Stellar and gain confidence in their correctness.
Cite as
Álvaro García-Pérez and Maria A. Schett. Deconstructing Stellar Consensus. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 5:1-5:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{garciaperez_et_al:LIPIcs.OPODIS.2019.5,
author = {Garc{\'\i}a-P\'{e}rez, \'{A}lvaro and Schett, Maria A.},
title = {{Deconstructing Stellar Consensus}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {5:1--5:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.5},
URN = {urn:nbn:de:0030-drops-117910},
doi = {10.4230/LIPIcs.OPODIS.2019.5},
annote = {Keywords: Blockchain, Consensus protocol, Stellar, Byzantine quorum systems}
}
Document
Byzantine-Tolerant Set-Constrained Delivery Broadcast
Abstract
Set-Constrained Delivery Broadcast (SCD-broadcast), recently introduced at ICDCN 2018, is a high-level communication abstraction that captures ordering properties not between individual messages but between sets of messages. More precisely, it allows processes to broadcast messages and deliver sets of messages, under the constraint that if a process delivers a set containing a message m before a set containing a message m', then no other process delivers first a set containing m' and later a set containing m. It has been shown that SCD-broadcast and read/write registers are computationally equivalent, and an algorithm implementing SCD-broadcast is known in the context of asynchronous message passing systems prone to crash failures.
This paper introduces a Byzantine-tolerant SCD-broadcast algorithm, which we call BSCD-broadcast. Our proposed algorithm assumes an underlying basic Byzantine-tolerant reliable broadcast abstraction. We first introduce an intermediary communication primitive, Byzantine FIFO broadcast (BFIFO-broadcast), which we then use as a primitive in our final BSCD-broadcast algorithm. Unlike the original SCD-broadcast algorithm that is tolerant to up to t<n/2 crashing processes, and unlike the underlying Byzantine reliable broadcast primitive that is tolerant to up to t<n/3 Byzantine processes, our BSCD-broadcast algorithm is tolerant to up to t<n/4 Byzantine processes. As an illustration of the high abstraction power provided by the BSCD-broadcast primitive, we show that it can be used to implement a Byzantine-tolerant read/write snapshot object in an extremely simple way.
Cite as
Alex Auvolat, Michel Raynal, and François Taïani. Byzantine-Tolerant Set-Constrained Delivery Broadcast. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 6:1-6:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{auvolat_et_al:LIPIcs.OPODIS.2019.6,
author = {Auvolat, Alex and Raynal, Michel and Ta\"{i}ani, Fran\c{c}ois},
title = {{Byzantine-Tolerant Set-Constrained Delivery Broadcast}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {6:1--6:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.6},
URN = {urn:nbn:de:0030-drops-117922},
doi = {10.4230/LIPIcs.OPODIS.2019.6},
annote = {Keywords: Algorithm, Asynchronous system, Byzantine process, Communication abstraction, Distributed computing, Distributed software engineering, Fault-tolerance, Message-passing, Modularity, Read/write snapshot object, Reliable broadcast, Set-constrained message delivery}
}
Document
Asymmetric Distributed Trust
Abstract
Quorum systems are a key abstraction in distributed fault-tolerant computing for capturing trust assumptions. They can be found at the core of many algorithms for implementing reliable broadcasts, shared memory, consensus and other problems. This paper introduces asymmetric Byzantine quorum systems that model subjective trust. Every process is free to choose which combinations of other processes it trusts and which ones it considers faulty. Asymmetric quorum systems strictly generalize standard Byzantine quorum systems, which have only one global trust assumption for all processes. This work also presents protocols that implement abstractions of shared memory and broadcast primitives with processes prone to Byzantine faults and asymmetric trust. The model and protocols pave the way for realizing more elaborate algorithms with asymmetric trust.
Cite as
Christian Cachin and Björn Tackmann. Asymmetric Distributed Trust. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 7:1-7:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{cachin_et_al:LIPIcs.OPODIS.2019.7,
author = {Cachin, Christian and Tackmann, Bj\"{o}rn},
title = {{Asymmetric Distributed Trust}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {7:1--7:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.7},
URN = {urn:nbn:de:0030-drops-117933},
doi = {10.4230/LIPIcs.OPODIS.2019.7},
annote = {Keywords: Quorums, consensus, distributed trust, blockchains, cryptocurrencies}
}
Document
Uniform Partition in Population Protocol Model Under Weak Fairness
Abstract
We focus on a uniform partition problem in a population protocol model. The uniform partition problem aims to divide a population into k groups of the same size, where k is a given positive integer. In the case of k=2 (called uniform bipartition), a previous work clarified space complexity under various assumptions: 1) an initialized base station (BS) or no BS, 2) weak or global fairness, 3) designated or arbitrary initial states of agents, and 4) symmetric or asymmetric protocols, except for the setting that agents execute a protocol from arbitrary initial states under weak fairness in the model with an initialized base station. In this paper, we clarify the space complexity for this remaining setting. In this setting, we prove that P states are necessary and sufficient to realize asymmetric protocols, and that P+1 states are necessary and sufficient to realize symmetric protocols, where P is the known upper bound of the number of agents. From these results and the previous work, we have clarified the solvability of the uniform bipartition for each combination of assumptions. Additionally, we newly consider an assumption on a model of a non-initialized BS and clarify solvability and space complexity in the assumption. Moreover, the results in this paper can be applied to the case that k is an arbitrary integer (called uniform k-partition).
Cite as
Hiroto Yasumi, Fukuhito Ooshita, and Michiko Inoue. Uniform Partition in Population Protocol Model Under Weak Fairness. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 8:1-8:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{yasumi_et_al:LIPIcs.OPODIS.2019.8,
author = {Yasumi, Hiroto and Ooshita, Fukuhito and Inoue, Michiko},
title = {{Uniform Partition in Population Protocol Model Under Weak Fairness}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {8:1--8:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.8},
URN = {urn:nbn:de:0030-drops-117947},
doi = {10.4230/LIPIcs.OPODIS.2019.8},
annote = {Keywords: population protocol, uniform k-partition, distributed protocol}
}
Document
Split and Migrate: Resource-Driven Placement and Discovery of Microservices at the Edge
Abstract
Microservices architectures combine the use of fine-grained and independently-scalable services with lightweight communication protocols, such as REST calls over HTTP. Microservices bring flexibility to the development and deployment of application back-ends in the cloud.
Applications such as collaborative editing tools require frequent interactions between the front-end running on users' machines and a back-end formed of multiple microservices. User-perceived latencies depend on their connection to microservices, but also on the interaction patterns between these services and their databases. Placing services at the edge of the network, closer to the users, is necessary to reduce user-perceived latencies. It is however difficult to decide on the placement of complete stateful microservices at one specific core or edge location without trading between a latency reduction for some users and a latency increase for the others.
We present how to dynamically deploy microservices on a combination of core and edge resources to systematically reduce user-perceived latencies. Our approach enables the split of stateful microservices, and the placement of the resulting splits on appropriate core and edge sites. Koala, a decentralized and resource-driven service discovery middleware, enables REST calls to reach and use the appropriate split, with only minimal changes to a legacy microservices application. Locality awareness using network coordinates further enables to automatically migrate services split and follow the location of the users. We confirm the effectiveness of our approach with a full prototype and an application to ShareLatex, a microservices-based collaborative editing application.
Cite as
Genc Tato, Marin Bertier, Etienne Rivière, and Cédric Tedeschi. Split and Migrate: Resource-Driven Placement and Discovery of Microservices at the Edge. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 9:1-9:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{tato_et_al:LIPIcs.OPODIS.2019.9,
author = {Tato, Genc and Bertier, Marin and Rivi\`{e}re, Etienne and Tedeschi, C\'{e}dric},
title = {{Split and Migrate: Resource-Driven Placement and Discovery of Microservices at the Edge}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {9:1--9:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.9},
URN = {urn:nbn:de:0030-drops-117954},
doi = {10.4230/LIPIcs.OPODIS.2019.9},
annote = {Keywords: Distributed applications, Microservices, State management, Edge computing}
}
Document
HaTS: Hardware-Assisted Transaction Scheduler
Abstract
In this paper we present HaTS, a Hardware-assisted Transaction Scheduler. HaTS improves performance of concurrent applications by classifying the executions of their atomic blocks (or in-memory transactions) into scheduling queues, according to their so called conflict indicators. The goal is to group those transactions that are conflicting while letting non-conflicting transactions proceed in parallel. Two core innovations characterize HaTS. First, HaTS does not assume the availability of precise information associated with incoming transactions in order to proceed with the classification. It relaxes this assumption by exploiting the inherent conflict resolution provided by Hardware Transactional Memory (HTM). Second, HaTS dynamically adjusts the number of the scheduling queues in order to capture the actual application contention level. Performance results using the STAMP benchmark suite show up to 2x improvement over state-of-the-art HTM-based scheduling techniques.
Cite as
Zhanhao Chen, Ahmed Hassan, Masoomeh Javidi Kishi, Jacob Nelson, and Roberto Palmieri. HaTS: Hardware-Assisted Transaction Scheduler. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 10:1-10:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{chen_et_al:LIPIcs.OPODIS.2019.10,
author = {Chen, Zhanhao and Hassan, Ahmed and Kishi, Masoomeh Javidi and Nelson, Jacob and Palmieri, Roberto},
title = {{HaTS: Hardware-Assisted Transaction Scheduler}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {10:1--10:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.10},
URN = {urn:nbn:de:0030-drops-117965},
doi = {10.4230/LIPIcs.OPODIS.2019.10},
annote = {Keywords: Transactions, Scheduling, Hardware Transactional Memory}
}
Document
Minha: Large-Scale Distributed Systems Testing Made Practical
Abstract
Testing large-scale distributed system software is still far from practical as the sheer scale needed and the inherent non-determinism make it very expensive to deploy and use realistically large environments, even with cloud computing and state-of-the-art automation. Moreover, observing global states without disturbing the system under test is itself difficult. This is particularly troubling as the gap between distributed algorithms and their implementations can easily introduce subtle bugs that are disclosed only with suitably large scale tests.
We address this challenge with Minha, a framework that virtualizes multiple JVM instances in a single JVM, thus simulating a distributed environment where each host runs on a separate machine, accessing dedicated network and CPU resources. The key contributions are the ability to run off-the-shelf concurrent and distributed JVM bytecode programs while at the same time scaling up to thousands of virtual nodes; and enabling global observation within standard software testing frameworks. Our experiments with two distributed systems show the usefulness of Minha in disclosing errors, evaluating global properties, and in scaling tests orders of magnitude with the same hardware resources.
Cite as
Nuno Machado, Francisco Maia, Francisco Neves, Fábio Coelho, and José Pereira. Minha: Large-Scale Distributed Systems Testing Made Practical. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 11:1-11:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{machado_et_al:LIPIcs.OPODIS.2019.11,
author = {Machado, Nuno and Maia, Francisco and Neves, Francisco and Coelho, F\'{a}bio and Pereira, Jos\'{e}},
title = {{Minha: Large-Scale Distributed Systems Testing Made Practical}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {11:1--11:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.11},
URN = {urn:nbn:de:0030-drops-117979},
doi = {10.4230/LIPIcs.OPODIS.2019.11},
annote = {Keywords: Distributed software testing, Large scale distributed systems, Simulation}
}
Document
Fast Lean Erasure-Coded Atomic Memory Object
Abstract
In this work, we propose FLECKS, an algorithm which implements atomic memory objects in a multi-writer multi-reader (MWMR) setting in asynchronous networks and server failures. FLECKS substantially reduces storage and communication costs over its replication-based counterparts by employing erasure-codes. FLECKS outperforms the previously proposed algorithms in terms of the metrics that to deliver good performance such as storage cost per object, communication cost a high fault-tolerance of clients and servers, guaranteed liveness of operation, and a given number of communication rounds per operation, etc. We provide proofs for liveness and atomicity properties of FLECKS and derive worst-case latency bounds for the operations. We implemented and deployed FLECKS in cloud-based clusters and demonstrate that FLECKS has substantially lower storage and bandwidth costs, and significantly lower latency of operations than the replication-based mechanisms.
Cite as
Kishori M. Konwar, N. Prakash, Muriel Médard, and Nancy Lynch. Fast Lean Erasure-Coded Atomic Memory Object. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 12:1-12:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{konwar_et_al:LIPIcs.OPODIS.2019.12,
author = {Konwar, Kishori M. and Prakash, N. and M\'{e}dard, Muriel and Lynch, Nancy},
title = {{Fast Lean Erasure-Coded Atomic Memory Object}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {12:1--12:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.12},
URN = {urn:nbn:de:0030-drops-117988},
doi = {10.4230/LIPIcs.OPODIS.2019.12},
annote = {Keywords: Atomicity, Distributed Storage System, Erasure-codes}
}
Document
Interactive Coding Resilient to an Unknown Number of Erasures
Abstract
We consider distributed computations between two parties carried out over a noisy channel that may erase messages. Following a noise model proposed by Dani et al. (2018), the noise level observed by the parties during the computation in our setting is arbitrary and a priori unknown to the parties.
We develop interactive coding schemes that adapt to the actual level of noise and correctly execute any two-party computation. Namely, in case the channel erases T transmissions, the coding scheme will take N+2T transmissions using an alphabet of size 4 (alternatively, using 2N+4T transmissions over a binary channel) to correctly simulate any binary protocol that takes N transmissions assuming a noiseless channel. We can further reduce the communication to N+T by relaxing the communication model and allowing parties to remain silent rather than forcing them to communicate in every round of the coding scheme.
Our coding schemes are efficient, deterministic, have linear overhead both in their communication and round complexity, and succeed (with probability 1) regardless of the number of erasures T.
Cite as
Ran Gelles and Siddharth Iyer. Interactive Coding Resilient to an Unknown Number of Erasures. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 13:1-13:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{gelles_et_al:LIPIcs.OPODIS.2019.13,
author = {Gelles, Ran and Iyer, Siddharth},
title = {{Interactive Coding Resilient to an Unknown Number of Erasures}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {13:1--13:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.13},
URN = {urn:nbn:de:0030-drops-117999},
doi = {10.4230/LIPIcs.OPODIS.2019.13},
annote = {Keywords: Interactive coding, erasure channels, distributed computation with noise, unbounded noise}
}
Document
A Generic Undo Support for State-Based CRDTs
Abstract
CRDTs (Conflict-free Replicated Data Types) have properties desirable for large-scale distributed systems with variable network latency or transient partitions. With CRDT, data are always available for local updates and data states converge when the replicas have incorporated the same updates. Undo is useful for correcting human mistakes and for restoring system-wide invariant violated due to long delays or network partitions.
There is currently no generally applicable undo support for CRDTs. There are at least two reasons for this. First, there is currently no abstraction that we can practically use to capture the relations between undo and normal operations with respect to concurrency and causality. Second, using inverse operations as the existing partial solutions, the CRDT designer has to hard-code certain rules and design a new CRDT for almost every operation that needs undo support.
In this paper, we present an approach to generic support of undo for CRDTs. The approach consists of two major parts. We first work out an abstraction that captures the semantics of concurrent undo and redo operations through equivalence classes. The abstraction is a natural extension of undo and redo in sequential applications and is straightforward to implement in practice. By using this abstraction, we then device a mechanism to augment existing CRDTs. The mechanism provides an "out of the box" support for undo without the involvement of the CRDT designers. We also present a practical application of the approach in collaborative editing.
Cite as
Weihai Yu, Victorien Elvinger, and Claudia-Lavinia Ignat. A Generic Undo Support for State-Based CRDTs. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 14:1-14:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{yu_et_al:LIPIcs.OPODIS.2019.14,
author = {Yu, Weihai and Elvinger, Victorien and Ignat, Claudia-Lavinia},
title = {{A Generic Undo Support for State-Based CRDTs}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {14:1--14:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.14},
URN = {urn:nbn:de:0030-drops-118009},
doi = {10.4230/LIPIcs.OPODIS.2019.14},
annote = {Keywords: Data replication, eventual consistency, state-based CRDT, delta-state CRDT, concurrent undo}
}
Document
In Search of the Fastest Concurrent Union-Find Algorithm
Abstract
Union-Find (or Disjoint-Set Union) is one of the fundamental problems in computer science; it has been well-studied from both theoretical and practical perspectives in the sequential case. Recently, there has been mounting interest in analyzing this problem in the concurrent scenario, and several asymptotically-efficient algorithms have been proposed. Yet, to date, there is very little known about the practical performance of concurrent Union-Find.
This work addresses this gap. We evaluate and analyze the performance of several concurrent Union-Find algorithms and optimization strategies across a wide range of platforms (Intel, AMD, and ARM) and workloads (social, random, and road networks, as well as integrations into more complex algorithms). We first observe that, due to the limited computational cost, the number of induced cache misses is the critical determining factor for the performance of existing algorithms. We introduce new techniques to reduce this cost by storing node priorities implicitly and by using plain reads and writes in a way that does not affect the correctness of the algorithms. Finally, we show that Union-Find implementations are an interesting application for Transactional Memory (TM): one of the fastest algorithm variants we discovered is a sequential one that uses coarse-grained locking with the lock elision optimization to reduce synchronization cost and increase scalability.
Cite as
Dan Alistarh, Alexander Fedorov, and Nikita Koval. In Search of the Fastest Concurrent Union-Find Algorithm. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 15:1-15:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{alistarh_et_al:LIPIcs.OPODIS.2019.15,
author = {Alistarh, Dan and Fedorov, Alexander and Koval, Nikita},
title = {{In Search of the Fastest Concurrent Union-Find Algorithm}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {15:1--15:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.15},
URN = {urn:nbn:de:0030-drops-118012},
doi = {10.4230/LIPIcs.OPODIS.2019.15},
annote = {Keywords: union-find, concurrency, evaluation, benchmarks, hardware transactional memory}
}
Document
On Deterministic Linearizable Set Agreement Objects
Abstract
A recent work showed that, for all n and k, there is a linearizable (n,k)-set agreement object O_L that is equivalent to the (n,k)-set agreement task [David Yu Cheng Chan et al., 2017]: given O_L, it is possible to solve the (n,k)-set agreement task, and given any algorithm that solves the (n,k)-set agreement task (and registers), it is possible to implement O_L. This linearizable object O_L, however, is not deterministic. It turns out that there is also a deterministic (n,k)-set agreement object O_D that is equivalent to the (n,k)-set agreement task, but this deterministic object O_D is not linearizable. This raises the question whether there exists a deterministic and linearizable (n,k)-set agreement object that is equivalent to the (n,k)-set agreement task. Here we show that in general the answer is no: specifically, we prove that for all n ≥ 4, every deterministic linearizable (n,2)-set agreement object is strictly stronger than the (n,2)-set agreement task. We prove this by showing that, for all n ≥ 4, every deterministic and linearizable (n,2)-set agreement object (together with registers) can be used to solve 2-consensus, whereas it is known that the (n,2)-set agreement task cannot do so. For a natural subset of (n,2)-set agreement objects, we prove that this result holds even for n = 3.
Cite as
Felipe de Azevedo Piovezan, Vassos Hadzilacos, and Sam Toueg. On Deterministic Linearizable Set Agreement Objects. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 16:1-16:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{deazevedopiovezan_et_al:LIPIcs.OPODIS.2019.16,
author = {de Azevedo Piovezan, Felipe and Hadzilacos, Vassos and Toueg, Sam},
title = {{On Deterministic Linearizable Set Agreement Objects}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {16:1--16:15},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.16},
URN = {urn:nbn:de:0030-drops-118026},
doi = {10.4230/LIPIcs.OPODIS.2019.16},
annote = {Keywords: Asynchronous shared-memory systems, consensus, set agreement, deterministic objects}
}
Document
A Characterization of Consensus Solvability for Closed Message Adversaries
Abstract
Distributed computations in a synchronous system prone to message loss can be modeled as a game between a (deterministic) distributed algorithm versus an omniscient message adversary. The latter determines, for each round, the directed communication graph that specifies which messages can reach their destination. Message adversary definitions range from oblivious ones, which pick the communication graphs arbitrarily from a given set of candidate graphs, to general message adversaries, which are specified by the set of sequences of communication graphs (called admissible communication patterns) that they may generate. This paper provides a complete characterization of consensus solvability for closed message adversaries, where every inadmissible communication pattern has a finite prefix that makes all (infinite) extensions of this prefix inadmissible. Whereas every oblivious message adversary is closed, there are also closed message adversaries that are not oblivious. We provide a tight non-topological, purely combinatorial characterization theorem, which reduces consensus solvability to a simple condition on prefixes of the communication patterns. Our result not only non-trivially generalizes the known combinatorial characterization of the consensus solvability for oblivious message adversaries by Coulouma, Godard, and Peters (Theor. Comput. Sci., 2015), but also provides the first combinatorial characterization for this important class of message adversaries that is formulated directly on the prefixes of the communication patterns.
Cite as
Kyrill Winkler, Ulrich Schmid, and Yoram Moses. A Characterization of Consensus Solvability for Closed Message Adversaries. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 17:1-17:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{winkler_et_al:LIPIcs.OPODIS.2019.17,
author = {Winkler, Kyrill and Schmid, Ulrich and Moses, Yoram},
title = {{A Characterization of Consensus Solvability for Closed Message Adversaries}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {17:1--17:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.17},
URN = {urn:nbn:de:0030-drops-118038},
doi = {10.4230/LIPIcs.OPODIS.2019.17},
annote = {Keywords: Dynamic networks, Consensus, Message Adversary}
}
Document
An Efficient Universal Construction for Large Objects
Abstract
This paper presents L-UC, a universal construction that efficiently implements dynamic objects of large state in a wait-free manner. The step complexity of L-UC is O(n+kw), where n is the number of processes, k is the interval contention (i.e., the maximum number of active processes during the execution interval of an operation), and w is the worst-case time complexity to perform an operation on the sequential implementation of the simulated object. L-UC efficiently implements objects whose size can change dynamically. It improves upon previous universal constructions either by efficiently handling objects whose state is large and can change dynamically, or by achieving better step complexity.
Cite as
Panagiota Fatourou, Nikolaos D. Kallimanis, and Eleni Kanellou. An Efficient Universal Construction for Large Objects. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 18:1-18:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{fatourou_et_al:LIPIcs.OPODIS.2019.18,
author = {Fatourou, Panagiota and Kallimanis, Nikolaos D. and Kanellou, Eleni},
title = {{An Efficient Universal Construction for Large Objects}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {18:1--18:15},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.18},
URN = {urn:nbn:de:0030-drops-118049},
doi = {10.4230/LIPIcs.OPODIS.2019.18},
annote = {Keywords: universal construction, concurrent object, shared memory, simulation, wait-freedom, large object}
}
Document
Toward Linearizability Testing for Multi-Word Persistent Synchronization Primitives
Abstract
Persistent memory makes it possible to recover in-memory data structures following a failure instead of rebuilding them from state saved in slow secondary storage. Implementing such recoverable data structures correctly is challenging as their underlying algorithms must deal with both parallelism and failures, which makes them especially susceptible to programming errors. Traditional proofs of correctness should therefore be combined with other methods, such as model checking or software testing, to minimize the likelihood of uncaught defects. This research focuses specifically on the algorithmic principles of software testing, particularly linearizability analysis, for multi-word persistent synchronization primitives such as conditional swap operations. We describe an efficient decision procedure for linearizability in this context, and discuss its practical applications in detecting previously-unknown bugs in implementations of multi-word persistent primitives.
Cite as
Diego Cepeda, Sakib Chowdhury, Nan Li, Raphael Lopez, Xinzhe Wang, and Wojciech Golab. Toward Linearizability Testing for Multi-Word Persistent Synchronization Primitives. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 19:1-19:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{cepeda_et_al:LIPIcs.OPODIS.2019.19,
author = {Cepeda, Diego and Chowdhury, Sakib and Li, Nan and Lopez, Raphael and Wang, Xinzhe and Golab, Wojciech},
title = {{Toward Linearizability Testing for Multi-Word Persistent Synchronization Primitives}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {19:1--19:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.19},
URN = {urn:nbn:de:0030-drops-118050},
doi = {10.4230/LIPIcs.OPODIS.2019.19},
annote = {Keywords: Shared memory, persistent memory, synchronization, multi-word primitives, concurrency, correctness, software testing}
}
Document
Consensus in Equilibrium: Can One Against All Decide Fairly?
Abstract
Is there an equilibrium for distributed consensus when all agents except one collude to steer the decision value towards their preference? If an equilibrium exists, then an n-1 size coalition cannot do better by deviating from the algorithm, even if it prefers a different decision value. We show that an equilibrium exists under this condition only if the number of agents in the network is odd and the decision is binary (among two possible input values). That is, in this framework we provide a separation between binary and multi-valued consensus. Moreover, the input and output distribution must be uniform, regardless of the communication model (synchronous or asynchronous). Furthermore, we define a new problem - Resilient Input Sharing (RIS), and use it to find an iff condition for the (n-1)-resilient equilibrium for deterministic binary consensus, essentially showing that an equilibrium for deterministic consensus is equivalent to each agent learning all the other inputs in some strong sense. Finally, we note that (n-2)-resilient equilibrium for binary consensus is possible for any n. The case of (n-2)-resilient equilibrium for multi-valued consensus is left open.
Cite as
Itay Harel, Amit Jacob-Fanani, Moshe Sulamy, and Yehuda Afek. Consensus in Equilibrium: Can One Against All Decide Fairly?. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 20:1-20:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{harel_et_al:LIPIcs.OPODIS.2019.20,
author = {Harel, Itay and Jacob-Fanani, Amit and Sulamy, Moshe and Afek, Yehuda},
title = {{Consensus in Equilibrium: Can One Against All Decide Fairly?}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {20:1--20:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.20},
URN = {urn:nbn:de:0030-drops-118065},
doi = {10.4230/LIPIcs.OPODIS.2019.20},
annote = {Keywords: distributed computing, game theory, rational agents, consensus}
}
Document
The Evolutionary Price of Anarchy: Locally Bounded Agents in a Dynamic Virus Game
Abstract
The Price of Anarchy (PoA) is a well-established game-theoretic concept to shed light on coordination issues arising in open distributed systems. Leaving agents to selfishly optimize comes with the risk of ending up in sub-optimal states (in terms of performance and/or costs), compared to a centralized system design. However, the PoA relies on strong assumptions about agents' rationality (e.g., resources and information) and interactions, whereas in many distributed systems agents interact locally with bounded resources. They do so repeatedly over time (in contrast to "one-shot games"), and their strategies may evolve.
Using a more realistic evolutionary game model, this paper introduces a realized evolutionary Price of Anarchy (ePoA). The ePoA allows an exploration of equilibrium selection in dynamic distributed systems with multiple equilibria, based on local interactions of simple memoryless agents.
Considering a fundamental game related to virus propagation on networks, we present analytical bounds on the ePoA in basic network topologies and for different strategy update dynamics. In particular, deriving stationary distributions of the stochastic evolutionary process, we find that the Nash equilibria are not always the most abundant states, and that different processes can feature significant off-equilibrium behavior, leading to a significantly higher ePoA compared to the PoA studied traditionally in the literature.
Cite as
Laura Schmid, Krishnendu Chatterjee, and Stefan Schmid. The Evolutionary Price of Anarchy: Locally Bounded Agents in a Dynamic Virus Game. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 21:1-21:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{schmid_et_al:LIPIcs.OPODIS.2019.21,
author = {Schmid, Laura and Chatterjee, Krishnendu and Schmid, Stefan},
title = {{The Evolutionary Price of Anarchy: Locally Bounded Agents in a Dynamic Virus Game}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {21:1--21:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.21},
URN = {urn:nbn:de:0030-drops-118071},
doi = {10.4230/LIPIcs.OPODIS.2019.21},
annote = {Keywords: Evolutionary Games, Virus Propagation, Price of Anarchy, Analysis}
}
Document
Tight Bounds on Distributed Exploration of Temporal Graphs
Abstract
Temporal graphs (or evolving graphs) are time-varying graphs where time is assumed to be discrete. In this paper, we consider for the first time the problem of exploring temporal graphs of arbitrary unknown topology. We study the feasibility of exploration, under both the Fsync and Ssync schedulers, focusing on the number of agents necessary and sufficient to explore such graphs.
We first consider the minimal (i.e., less restrictive) assumption on the dynamics of the graph under which exploration is still feasible: temporal connectivity. Let ℋ be the class of temporally connected graphs; we show that for any temporal graph ? ∈ ℋ the number of agents sufficient to perform exploration is related to the number of its transient edges, a parameter η(?) we call evanescence of the graph. More precisely, any ? ∈ ℋ can be explored by a team of k ≥ 2 η(?) +1 agents; this bound is tight as we prove there are ? ∈ ℋ that cannot be explored by 2 η(?) agents.
We then turn our attention to the well-known stronger assumption on the dynamics of the graph, called 1-interval connectivity: the graph is connected at any time step. Let ? ⊂ ℋ be the class of these always-connected temporal graphs. For this class, we prove the existence of a difference between Fsync and Ssync when there is a bound ? on the number of edges missing at each time. In fact, we show a tight bound of 2 ? +1 on the number of agents necessary and sufficient in Ssync, and a smaller tight bound of 2 ? in Fsync. As a corollary, we re-establish two recently published bounds for 1-interval connected rings.
Cite as
Tsuyoshi Gotoh, Paola Flocchini, Toshimitsu Masuzawa, and Nicola Santoro. Tight Bounds on Distributed Exploration of Temporal Graphs. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 22:1-22:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{gotoh_et_al:LIPIcs.OPODIS.2019.22,
author = {Gotoh, Tsuyoshi and Flocchini, Paola and Masuzawa, Toshimitsu and Santoro, Nicola},
title = {{Tight Bounds on Distributed Exploration of Temporal Graphs}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {22:1--22:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.22},
URN = {urn:nbn:de:0030-drops-118082},
doi = {10.4230/LIPIcs.OPODIS.2019.22},
annote = {Keywords: Distributed algorithm, Mobile agents, Exploration of dynamic networks, Arbitrary footprint}
}
Document
Parallel and Distributed Algorithms for the Housing Allocation Problem
Abstract
We propose parallel and distributed algorithms for the housing allocation problem. In this problem, there is a set of agents and a set of houses. Each agent has a strict preference list for a subset of houses. We need to find a matching for agents to houses such that some criterion is optimized. One such criterion which has attracted much attention is Pareto optimality. A matching is Pareto optimal if no coalition of agents can be strictly better off by exchanging houses among themselves. We also study the housing market problem, a variant of the housing allocation problem, where each agent initially owns a house. In addition to Pareto optimality, we are also interested in finding the a matching in the core of a housing market. A matching is in the core if there is no coalition of agents that can be better off by breaking away from other agents and switching houses only among themselves in the initial allocation.
In the first part of this work, we show that computing a Pareto optimal matching of a house allocation is in CC and computing a matching in the core of a housing market is CC-hard, where CC is the class of problems logspace reducible to the comparator circuit value problem. Given a matching of agents to houses, we show that verifying whether it is Pareto optimal is in NC. We also show that verifying whether it is in the core can be done in NC. We then give an algorithm to show that computing a maximum cardinality Pareto optimal matching for the housing allocation problem is in RNC² and quasi-NC².
In the second part of this work, we present a distributed version of the top trading cycle algorithm for finding a matching in the core of a housing market. To that end, we first present two algorithms for finding all the disjoint cycles in a functional graph. The first algorithm is a Las Vegas algorithm which terminates in O(log l) rounds with high probability, where l is the length of the longest cycle. The second algorithm is a deterministic algorithm which terminates in O(log* n log l) rounds, where n is the number of nodes in the graph. Both algorithms work in the synchronous distributed model and use messages of size O(log n). By applying these two algorithms for finding cycles in a functional graph, we give the distributed top trading cycle algorithm which terminates in O(n) rounds and requires O(n²) messages.
Cite as
Xiong Zheng and Vijay K. Garg. Parallel and Distributed Algorithms for the Housing Allocation Problem. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 23:1-23:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{zheng_et_al:LIPIcs.OPODIS.2019.23,
author = {Zheng, Xiong and Garg, Vijay K.},
title = {{Parallel and Distributed Algorithms for the Housing Allocation Problem}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {23:1--23:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.23},
URN = {urn:nbn:de:0030-drops-118090},
doi = {10.4230/LIPIcs.OPODIS.2019.23},
annote = {Keywords: Parallel Algorithm, Distributed Algorithm, Housing Allocation, Housing Markets, Pareto optimality}
}
Document
Oblivious Permutations on the Plane
Abstract
We consider a distributed system of n identical mobile robots operating in the two dimensional Euclidian plane. As in the previous studies, we consider the robots to be anonymous, oblivious, dis-oriented, and without any communication capabilities, operating based on the Look-Compute-Move model where the next location of a robot depends only on its view of the current configuration. Even in this seemingly weak model, most formation problems which require constructing specific configurations, can be solved quite easily when the robots are fully synchronized with each other. In this paper we introduce and study a new class of problems which, unlike the studied formation problems, cannot always be solved even in the fully synchronous model with atomic and rigid moves. This class of problems requires the robots to permute their locations in the plane. In particular, we are interested in implementing two special types of permutations - permutations without any fixed points and permutations of order n. The former (called Move-All) requires each robot to visit at least two of the initial locations, while the latter (called Visit-All) requires every robot to visit each of the initial locations in a periodic manner. We provide a characterization of the solvability of these problems, showing the main challenges in solving this class of problems for mobile robots. We also provide algorithms for the feasible cases, in particular distinguishing between one-step algorithms (where each configuration must be a permutation of the original configuration) and multi-step algorithms (which allow intermediate configurations). These results open a new research direction in mobile distributed robotics which has not been investigated before.
Cite as
Shantanu Das, Giuseppe A. Di Luna, Paola Flocchini, Nicola Santoro, Giovanni Viglietta, and Masafumi Yamashita. Oblivious Permutations on the Plane. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 24:1-24:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{das_et_al:LIPIcs.OPODIS.2019.24,
author = {Das, Shantanu and Di Luna, Giuseppe A. and Flocchini, Paola and Santoro, Nicola and Viglietta, Giovanni and Yamashita, Masafumi},
title = {{Oblivious Permutations on the Plane}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {24:1--24:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.24},
URN = {urn:nbn:de:0030-drops-118103},
doi = {10.4230/LIPIcs.OPODIS.2019.24},
annote = {Keywords: Distributed Algorithms, Mobile Robots, Fully synchronous, Oblivious, Permutations, Chirality, Sequence of configurations}
}
Document
On Memory, Communication, and Synchronous Schedulers When Moving and Computing
Abstract
We investigate the computational power of distributed systems whose autonomous computational entities, called robots, move and operate in the 2-dimensional Euclidean plane in synchronous Look-Compute-Move (LCM) cycles. Specifically, we focus on the power of persistent memory and that of explicit communication, and on their computational relationship.
In the most common model, OBLOT, the robots are oblivious (no persistent memory) and silent (no explicit means of communication). In contrast, in the LUMI model, each robot is equipped with a constant-sized persistent memory (called light), visible to all the robots; hence, these luminous robots are capable in each cycle of both remembering and communicating. Since luminous robots are computationally more powerful than the standard oblivious one, immediate important questions are about the individual computational power of persistent memory and of explicit communication. In particular, which of the two capabilities, memory or communication, is more important? in other words, is it better to remember or to communicate ?
In this paper we address these questions, focusing on two sub-models of LUMI: FSTA, where the robots have a constant-size persistent memory but are silent; and FCOM, where the robots can communicate a constant number of bits but are oblivious. We analyze the relationship among all these models and provide a complete exhaustive map of their computational relationship. Among other things, we prove that communication is more powerful than persistent memory under the fully synchronous scheduler Fsynch, while they are incomparable under the semi-synchronous scheduler Ssynch.
Cite as
Paola Flocchini, Nicola Santoro, and Koichi Wada. On Memory, Communication, and Synchronous Schedulers When Moving and Computing. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 25:1-25:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{flocchini_et_al:LIPIcs.OPODIS.2019.25,
author = {Flocchini, Paola and Santoro, Nicola and Wada, Koichi},
title = {{On Memory, Communication, and Synchronous Schedulers When Moving and Computing}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {25:1--25:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.25},
URN = {urn:nbn:de:0030-drops-118114},
doi = {10.4230/LIPIcs.OPODIS.2019.25},
annote = {Keywords: Look-Compute-Move, Oblivious mobile robots, Robots with lights, Memory versus Communication, Moving and Computing}
}
Document
Lower Bounds for Shoreline Searching With 2 or More Robots
Abstract
Searching for a line on the plane with n unit speed robots is a classic online problem that dates back to the 50’s, and for which competitive ratio upper bounds are known for every n ≥ 1, see [Baeza-Yates and Schott, 1995]. In this work we improve the best lower bound known for n=2 robots [Baeza-Yates and Schott, 1995] from 1.5993 to 3. Moreover we prove that the competitive ratio is at least √{3} for n=3 robots, and at least 1/cos ({π/n}) for n ≥ 4 robots. Our lower bounds match the best upper bounds known for n ≥ 4, hence resolving these cases. To the best of our knowledge, these are the first lower bounds proven for the cases n ≥ 3 of this several decades old problem.
Cite as
Sumi Acharjee, Konstantinos Georgiou, Somnath Kundu, and Akshaya Srinivasan. Lower Bounds for Shoreline Searching With 2 or More Robots. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 26:1-26:11, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{acharjee_et_al:LIPIcs.OPODIS.2019.26,
author = {Acharjee, Sumi and Georgiou, Konstantinos and Kundu, Somnath and Srinivasan, Akshaya},
title = {{Lower Bounds for Shoreline Searching With 2 or More Robots}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {26:1--26:11},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.26},
URN = {urn:nbn:de:0030-drops-118121},
doi = {10.4230/LIPIcs.OPODIS.2019.26},
annote = {Keywords: 2-Dimensional Search, Online Algorithms, Competitive Analysis, Lower Bounds}
}
Document
Gathering on Rings for Myopic Asynchronous Robots With Lights
Abstract
We investigate gathering algorithms for asynchronous autonomous mobile robots moving in uniform ring-shaped networks. Different from most work using the Look-Compute-Move (LCM) model, we assume that robots have limited visibility and lights. That is, robots can observe nodes only within a certain fixed distance, and emit a color from a set of constant number of colors. We consider gathering algorithms depending on two parameters related to the initial configuration: M_{init}, which denotes the number of nodes between two border nodes, and O_{init}, which denotes the number of nodes hosting robots between two border nodes. In both cases, a border node is a node hosting one or more robots that cannot see other robots on at least one side. Our main contribution is to prove that, if M_{init} or O_{init} is odd, gathering is always feasible with three or four colors. The proposed algorithms do not require additional assumptions, such as knowledge of the number of robots, multiplicity detection capabilities, or the assumption of towerless initial configurations. These results demonstrate the power of lights to achieve gathering of robots with limited visibility.
Cite as
Sayaka Kamei, Anissa Lamani, Fukuhito Ooshita, Sébastien Tixeuil, and Koichi Wada. Gathering on Rings for Myopic Asynchronous Robots With Lights. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 27:1-27:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{kamei_et_al:LIPIcs.OPODIS.2019.27,
author = {Kamei, Sayaka and Lamani, Anissa and Ooshita, Fukuhito and Tixeuil, S\'{e}bastien and Wada, Koichi},
title = {{Gathering on Rings for Myopic Asynchronous Robots With Lights}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {27:1--27:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.27},
URN = {urn:nbn:de:0030-drops-118139},
doi = {10.4230/LIPIcs.OPODIS.2019.27},
annote = {Keywords: LCM robot system, ASYNC schedulers, myopic, luminous, ring networks}
}
Document
Optimal Register Construction in M&M Systems
Abstract
Motivated by recent distributed systems technology, Aguilera et al. introduced a hybrid model of distributed computing, called message-and-memory model or m&m model for short [Marcos K. Aguilera et al., 2018]. In this model, processes can communicate by message passing and also by accessing some shared memory. We consider the basic problem of implementing an atomic single-writer multi-reader (SWMR) register shared by all the processes in m&m systems. Specifically, we give an algorithm that implements such a register in m&m systems and show that it is optimal in the number of process crashes that it can tolerate. This generalizes the well-known implementation of an atomic SWMR register in a pure message-passing system [Attiya et al., 1995].
Cite as
Vassos Hadzilacos, Xing Hu, and Sam Toueg. Optimal Register Construction in M&M Systems. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 28:1-28:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{hadzilacos_et_al:LIPIcs.OPODIS.2019.28,
author = {Hadzilacos, Vassos and Hu, Xing and Toueg, Sam},
title = {{Optimal Register Construction in M\&M Systems}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {28:1--28:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.28},
URN = {urn:nbn:de:0030-drops-118148},
doi = {10.4230/LIPIcs.OPODIS.2019.28},
annote = {Keywords: asynchronous distributed system, shared memory, message passing}
}
Document
Linearizable Replicated State Machines With Lattice Agreement
Abstract
This paper studies the lattice agreement problem in asynchronous systems and explores its application to building a linearizable replicated state machine (RSM). First, we propose an algorithm to solve the lattice agreement problem in O(log f) asynchronous rounds, where f is the number of crash failures that the system can tolerate. This is an exponential improvement over the previous best upper bound of O(f). Second, Faleiro et al have shown in [Faleiro et al. PODC, 2012] that combination of conflict-free data types and lattice agreement protocols can be applied to implement a linearizable RSM. They give a Paxos style lattice agreement protocol, which can be adapted to implement a linearizable RSM and guarantee that a command by a client can be learned in at most O(n) message delays, where n is the number of proposers. Later, Xiong et al in [Xiong et al. DISC, 2018] gave a lattice agreement protocol which improves the O(n) message delay guarantee to O(f). However, neither of the protocols is practical for building a linearizable RSM. Thus, in the second part of the paper, we first give an improved protocol based on the one proposed by Xiong et al. Then, we implement a simple linearizable RSM using our improved protocol and compare our implementation with an open source Java implementation of Paxos. Results show that better performance can be obtained by using lattice agreement based protocols to implement a linearizable RSM compared to traditional consensus based protocols.
Cite as
Xiong Zheng, Vijay K. Garg, and John Kaippallimalil. Linearizable Replicated State Machines With Lattice Agreement. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 29:1-29:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{zheng_et_al:LIPIcs.OPODIS.2019.29,
author = {Zheng, Xiong and Garg, Vijay K. and Kaippallimalil, John},
title = {{Linearizable Replicated State Machines With Lattice Agreement}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {29:1--29:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.29},
URN = {urn:nbn:de:0030-drops-118158},
doi = {10.4230/LIPIcs.OPODIS.2019.29},
annote = {Keywords: Lattice Agreement, Generalized Lattice Agreement, Replicated State Machine, Consensus}
}
Document
Exact Byzantine Consensus on Arbitrary Directed Graphs Under Local Broadcast Model
Abstract
We consider Byzantine consensus in a synchronous system where nodes are connected by a network modeled as a directed graph, i.e., communication links between neighboring nodes are not necessarily bi-directional. The directed graph model is motivated by wireless networks wherein asymmetric communication links can occur. In the classical point-to-point communication model, a message sent on a communication link is private between the two nodes on the link. This allows a Byzantine faulty node to equivocate, i.e., send inconsistent information to its neighbors. This paper considers the local broadcast model of communication, wherein transmission by a node is received identically by all of its outgoing neighbors, effectively depriving the faulty nodes of the ability to equivocate.
Prior work has obtained sufficient and necessary conditions on undirected graphs to be able to achieve Byzantine consensus under the local broadcast model. In this paper, we obtain tight conditions on directed graphs to be able to achieve Byzantine consensus with binary inputs under the local broadcast model. The results obtained in the paper provide insights into the trade-off between directionality of communication links and the ability to achieve consensus.
Cite as
Muhammad Samir Khan, Lewis Tseng, and Nitin H. Vaidya. Exact Byzantine Consensus on Arbitrary Directed Graphs Under Local Broadcast Model. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 30:1-30:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{khan_et_al:LIPIcs.OPODIS.2019.30,
author = {Khan, Muhammad Samir and Tseng, Lewis and Vaidya, Nitin H.},
title = {{Exact Byzantine Consensus on Arbitrary Directed Graphs Under Local Broadcast Model}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {30:1--30:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.30},
URN = {urn:nbn:de:0030-drops-118161},
doi = {10.4230/LIPIcs.OPODIS.2019.30},
annote = {Keywords: complexity and impossibility results for distributed computing, fault-tolerance, reliability}
}
Document
Reconfigurable Lattice Agreement and Applications
Abstract
Reconfiguration is one of the central mechanisms in distributed systems. Due to failures and connectivity disruptions, the very set of service replicas (or servers) and their roles in the computation may have to be reconfigured over time. To provide the desired level of consistency and availability to applications running on top of these servers, the clients of the service should be able to reach some form of agreement on the system configuration. We observe that this agreement is naturally captured via a lattice partial order on the system states. We propose an asynchronous implementation of reconfigurable lattice agreement that implies elegant reconfigurable versions of a large class of lattice abstract data types, such as max-registers and conflict detectors, as well as popular distributed programming abstractions, such as atomic snapshot and commit-adopt.
Cite as
Petr Kuznetsov, Thibault Rieutord, and Sara Tucci-Piergiovanni. Reconfigurable Lattice Agreement and Applications. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 31:1-31:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{kuznetsov_et_al:LIPIcs.OPODIS.2019.31,
author = {Kuznetsov, Petr and Rieutord, Thibault and Tucci-Piergiovanni, Sara},
title = {{Reconfigurable Lattice Agreement and Applications}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {31:1--31:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.31},
URN = {urn:nbn:de:0030-drops-118177},
doi = {10.4230/LIPIcs.OPODIS.2019.31},
annote = {Keywords: Reconfigurable services, lattice agreement}
}
Document
Towards Distributed Two-Stage Stochastic Optimization
Abstract
The weighted vertex cover problem is concerned with selecting a subset of the vertices that covers a target set of edges with the objective of minimizing the total cost of the selected vertices. We consider a variant of this classic combinatorial optimization problem where the target edge set is not fully known; rather, it is characterized by a probability distribution. Adhering to the model of two-stage stochastic optimization, the execution is divided into two stages so that in the first stage, the decision maker selects some of the vertices based on the probabilistic forecast of the target edge set. Then, in the second stage, the edges in the target set are revealed and in order to cover them, the decision maker can augment the vertex subset selected in the first stage with additional vertices. However, in the second stage, the vertex cost increases by some inflation factor, so the second stage selection becomes more expensive.
The current paper studies the two-stage stochastic vertex cover problem in the realm of distributed graph algorithms, where the decision making process (in both stages) is distributed among the vertices of the graph. By combining the stochastic optimization toolbox with recent advances in distributed algorithms for weighted vertex cover, we develop an algorithm that runs in time O(log (Δ) / ε), sends O(m) messages in total, and guarantees to approximate the optimal solution within a (3 + ε)-ratio, where m is the number of edges in the graph, Δ is its maximum degree, and 0 < ε < 1 is a performance parameter.
Cite as
Yuval Emek, Noga Harlev, and Taisuke Izumi. Towards Distributed Two-Stage Stochastic Optimization. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 32:1-32:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{emek_et_al:LIPIcs.OPODIS.2019.32,
author = {Emek, Yuval and Harlev, Noga and Izumi, Taisuke},
title = {{Towards Distributed Two-Stage Stochastic Optimization}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {32:1--32:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.32},
URN = {urn:nbn:de:0030-drops-118187},
doi = {10.4230/LIPIcs.OPODIS.2019.32},
annote = {Keywords: weighted vertex cover, distributed graph algorithms, two-stage stochastic optimization, primal-dual}
}
Document
Equivalence Classes and Conditional Hardness in Massively Parallel Computations
Abstract
The Massively Parallel Computation (MPC) model serves as a common abstraction of many modern large-scale data processing frameworks, and has been receiving increasingly more attention over the past few years, especially in the context of classical graph problems. So far, the only way to argue lower bounds for this model is to condition on conjectures about the hardness of some specific problems, such as graph connectivity on promise graphs that are either one cycle or two cycles, usually called the one cycle vs. two cycles problem. This is unlike the traditional arguments based on conjectures about complexity classes (e.g., P ≠ NP), which are often more robust in the sense that refuting them would lead to groundbreaking algorithms for a whole bunch of problems.
In this paper we present connections between problems and classes of problems that allow the latter type of arguments. These connections concern the class of problems solvable in a sublogarithmic amount of rounds in the MPC model, denoted by MPC(o(log N)), and some standard classes concerning space complexity, namely L and NL, and suggest conjectures that are robust in the sense that refuting them would lead to many surprisingly fast new algorithms in the MPC model. We also obtain new conditional lower bounds, and prove new reductions and equivalences between problems in the MPC model.
Cite as
Danupon Nanongkai and Michele Scquizzato. Equivalence Classes and Conditional Hardness in Massively Parallel Computations. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 33:1-33:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{nanongkai_et_al:LIPIcs.OPODIS.2019.33,
author = {Nanongkai, Danupon and Scquizzato, Michele},
title = {{Equivalence Classes and Conditional Hardness in Massively Parallel Computations}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {33:1--33:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.33},
URN = {urn:nbn:de:0030-drops-118194},
doi = {10.4230/LIPIcs.OPODIS.2019.33},
annote = {Keywords: Massively parallel computation, conditional hardness, fine-grained complexity}
}
Document
Sparse Hopsets in Congested Clique
Abstract
We give the first Congested Clique algorithm that computes a sparse hopset with polylogarithmic hopbound in polylogarithmic time. Given a graph G=(V,E), a (β,ε)-hopset H with "hopbound" β, is a set of edges added to G such that for any pair of nodes u and v in G there is a path with at most β hops in G ∪ H with length within (1+ε) of the shortest path between u and v in G. Our hopsets are significantly sparser than the recent construction of [Censor-Hillel et al., 2019], that constructs a hopset of size Õ (n^{3/2}), but with a smaller polylogarithmic hopbound. On the other hand, the previously known construction of sparse hopsets with polylogarithmic hopbound in the Congested Clique model, proposed by [Elkin and Neiman, 2018; Elkin and Neiman, 2019; Elkin and Neiman, 2019], all require polynomial rounds.
One tool that we use is an efficient algorithm that constructs an l-limited neighborhood cover, that may be of independent interest. Finally, as a side result, we also give a hopset construction in a variant of the low-memory Massively Parallel Computation model, with improved running time over existing algorithms.
Cite as
Yasamin Nazari. Sparse Hopsets in Congested Clique. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 34:1-34:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{nazari:LIPIcs.OPODIS.2019.34,
author = {Nazari, Yasamin},
title = {{Sparse Hopsets in Congested Clique}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {34:1--34:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.34},
URN = {urn:nbn:de:0030-drops-118207},
doi = {10.4230/LIPIcs.OPODIS.2019.34},
annote = {Keywords: Hopsets, Congested Clique, Shortest Paths, Massively Parallel Computation}
}
Document
Massively Parallel Approximate Distance Sketches
Abstract
Data structures that allow efficient distance estimation (distance oracles, distance sketches, etc.) have been extensively studied, and are particularly well studied in centralized models and classical distributed models such as CONGEST. We initiate their study in newer (and arguably more realistic) models of distributed computation: the Congested Clique model and the Massively Parallel Computation (MPC) model. We provide efficient constructions in both of these models, but our core results are for MPC. In MPC we give two main results: an algorithm that constructs stretch/space optimal distance sketches but takes a (small) polynomial number of rounds, and an algorithm that constructs distance sketches with worse stretch but that only takes polylogarithmic rounds.
Along the way, we show that other useful combinatorial structures can also be computed in MPC. In particular, one key component we use to construct distance sketches are an MPC construction of the hopsets of [Elkin and Neiman, 2016]. This result has additional applications such as the first polylogarithmic time algorithm for constant approximate single-source shortest paths for weighted graphs in the low memory MPC setting.
Cite as
Michael Dinitz and Yasamin Nazari. Massively Parallel Approximate Distance Sketches. In 23rd International Conference on Principles of Distributed Systems (OPODIS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 153, pp. 35:1-35:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{dinitz_et_al:LIPIcs.OPODIS.2019.35,
author = {Dinitz, Michael and Nazari, Yasamin},
title = {{Massively Parallel Approximate Distance Sketches}},
booktitle = {23rd International Conference on Principles of Distributed Systems (OPODIS 2019)},
pages = {35:1--35:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-133-7},
ISSN = {1868-8969},
year = {2020},
volume = {153},
editor = {Felber, Pascal and Friedman, Roy and Gilbert, Seth and Miller, Avery},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2019.35},
URN = {urn:nbn:de:0030-drops-118216},
doi = {10.4230/LIPIcs.OPODIS.2019.35},
annote = {Keywords: Distance Sketches, Massively Parallel Computation, Distance Oracles, Single-Source Shortest Paths}
}