eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
0
0
10.4230/LIPIcs.DISC.2019
article
LIPIcs, Volume 146, DISC'19, Complete Volume
Suomela, Jukka
1
Aalto University, Finland
LIPIcs, Volume 146, DISC'19, Complete Volume
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019/LIPIcs.DISC.2019.pdf
Software and its engineering, Distributed systems organizing principles; Computing methodologies, Distributed computing methodologies
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
0:i
0:xviii
10.4230/LIPIcs.DISC.2019.0
article
Front Matter, Table of Contents, Preface, Conference Organization
Suomela, Jukka
1
Aalto University, Finland
Front Matter, Table of Contents, Preface, Conference Organization
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.0/LIPIcs.DISC.2019.0.pdf
Front Matter
Table of Contents
Preface
Conference Organization
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
1:1
1:9
10.4230/LIPIcs.DISC.2019.1
article
Consensus with Max Registers
Aspnes, James
1
Er, He Yang
1
Department of Computer Science, Yale University, New Haven, CT, USA
We consider the problem of implementing randomized wait-free consensus from max registers under the assumption of an oblivious adversary. We show that max registers solve m-valued consensus for arbitrary m in expected O(log^* n) steps per process, beating the Omega(log m/log log m) lower bound for ordinary registers when m is large and the best previously known O(log log n) upper bound when m is small. A simple max-register implementation based on double-collect snapshots translates this result into an O(n log n) expected step implementation of m-valued consensus from n single-writer registers, improving on the best previously-known bound of O(n log^2 n) for single-writer registers.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.1/LIPIcs.DISC.2019.1.pdf
consensus
max register
single-writer register
oblivious adversary
shared memory
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
2:1
2:17
10.4230/LIPIcs.DISC.2019.2
article
Putting Strong Linearizability in Context: Preserving Hyperproperties in Programs That Use Concurrent Objects
Attiya, Hagit
1
https://orcid.org/0000-0002-8017-6457
Enea, Constantin
2
Technion - Israel Institute of Technology, Haifa, Israel
Université de Paris, IRIF, CNRS, F-75013 Paris, France
It has been observed that linearizability, the prevalent consistency condition for implementing concurrent objects, does not preserve some probability distributions. A stronger condition, called strong linearizability has been proposed, but its study has been somewhat ad-hoc. This paper investigates strong linearizability by casting it in the context of observational refinement of objects. We present a strengthening of observational refinement, which generalizes strong linearizability, obtaining several important implications.
When a concrete concurrent object refines another, more abstract object - often sequential - the correctness of a program employing the concrete object can be verified by considering its behaviors when using the more abstract object. This means that trace properties of a program using the concrete object can be proved by considering the program with the abstract object. This, however, does not hold for hyperproperties, including many security properties and probability distributions of events.
We define strong observational refinement, a strengthening of refinement that preserves hyperproperties, and prove that it is equivalent to the existence of forward simulations. We show that strong observational refinement generalizes strong linearizability. This implies that strong linearizability is also equivalent to forward simulation, and shows that strongly linearizable implementations can be composed both horizontally (i.e., locality) and vertically (i.e., with instantiation).
For situations where strongly linearizable implementations do not exist (or are less efficient), we argue that reasoning about hyperproperties of programs can be simplified by strong observational refinement of non-atomic abstract objects.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.2/LIPIcs.DISC.2019.2.pdf
Concurrent Objects
Linearizability
Hyperproperties
Forward Simulations
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
3:1
3:16
10.4230/LIPIcs.DISC.2019.3
article
Long-Lived Counters with Polylogarithmic Amortized Step Complexity
Baig, Mirza Ahad
1
2
3
Hendler, Danny
4
Milani, Alessia
1
Travers, Corentin
1
LaBRI, Bordeaux INP, France
CNRS, ReLaX, UMI2000, Siruseri, India
Chennai Mathematical Institute, Siruseri, India
Ben-Gurion University of the Negev, Beer-Sheva, Israel
A shared-memory counter is a well-studied and widely-used concurrent object. It supports two operations: An Inc operation that increases its value by 1 and a Read operation that returns its current value. Jayanti, Tan and Toueg [Jayanti et al., 2000] proved a linear lower bound on the worst-case step complexity of obstruction-free implementations, from read and write operations, of a large class of shared objects that includes counters. The lower bound leaves open the question of finding counter implementations with sub-linear amortized step complexity.
In this paper, we address this gap. We present the first wait-free n-process counter, implemented using only read and write operations, whose amortized operation step complexity is O(log^2 n) in all executions. This is the first non-blocking read/write counter algorithm that provides sub-linear amortized step complexity in executions of arbitrary length. Since a logarithmic lower bound on the amortized step complexity of obstruction-free counter implementations exists, our upper bound is optimal up to a logarithmic factor.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.3/LIPIcs.DISC.2019.3.pdf
Shared Memory
Wait-freedom
Counter
Amortized Complexity
Concurrent Objects
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
4:1
4:14
10.4230/LIPIcs.DISC.2019.4
article
Distributed Algorithms for Low Stretch Spanning Trees
Becker, Ruben
1
Emek, Yuval
2
Ghaffari, Mohsen
3
Lenzen, Christoph
4
Gran Sasso Science Institute, L'Aquila, Italy
Technion - Israel Institute of Technology, Haifa, Israel
ETH Zurich, Switzerland
MPI for Informatics, Saarland Informatics Campus, Saarbrücken, Germany
Given an undirected graph with integer edge lengths, we study the problem of approximating the distances in the graph by a spanning tree based on the notion of stretch. Our main contribution is a distributed algorithm in the CONGEST model of computation that constructs a random spanning tree with the guarantee that the expected stretch of every edge is O(log^{3} n), where n is the number of nodes in the graph. If the graph is unweighted, then this algorithm can be implemented to run in O(D) rounds, where D is the hop-diameter of the graph, thus being asymptotically optimal. In the weighted case, the run-time of our algorithm matches the currently best known bound for exact distance computations, i.e., O~ (min{sqrt{n D}, sqrt{n} D^{1 / 4} + n^{3 / 5} + D}). We stress that this is the first distributed construction of spanning trees leading to poly-logarithmic expected stretch with non-trivial running time.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.4/LIPIcs.DISC.2019.4.pdf
distributed graph algorithms
low-stretch spanning trees
CONGEST model
ball decomposition
star decomposition
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
5:1
5:15
10.4230/LIPIcs.DISC.2019.5
article
Optimal Distributed Covering Algorithms
Ben-Basat, Ran
1
https://orcid.org/0000-0003-0196-9190
Even, Guy
2
https://orcid.org/0000-0001-5407-330X
Kawarabayashi, Ken-ichi
3
https://orcid.org/0000-0001-6056-4287
Schwartzman, Gregory
3
https://orcid.org/0000-0002-8461-1479
Harvard University, Cambridge, MA, United States
Tel Aviv University, Tel Aviv, Israel
National Institute of Informatics, Tokyo, Japan
We present a time-optimal deterministic distributed algorithm for approximating a minimum weight vertex cover in hypergraphs of rank f. This problem is equivalent to the Minimum Weight Set Cover problem in which the frequency of every element is bounded by f. The approximation factor of our algorithm is (f+epsilon). Let Delta denote the maximum degree in the hypergraph. Our algorithm runs in the congest model and requires O(log{Delta} / log log Delta) rounds, for constants epsilon in (0,1] and f in N^+. This is the first distributed algorithm for this problem whose running time does not depend on the vertex weights nor the number of vertices. Thus adding another member to the exclusive family of provably optimal distributed algorithms.
For constant values of f and epsilon, our algorithm improves over the (f+epsilon)-approximation algorithm of [Fabian Kuhn et al., 2006] whose running time is O(log Delta + log W), where W is the ratio between the largest and smallest vertex weights in the graph. Our algorithm also achieves an f-approximation for the problem in O(f log n) rounds, improving over the classical result of [Samir Khuller et al., 1994] that achieves a running time of O(f log^2 n). Finally, for weighted vertex cover (f=2) our algorithm achieves a deterministic running time of O(log n), matching the randomized previously best result of [Koufogiannakis and Young, 2011].
We also show that integer covering-programs can be reduced to the Minimum Weight Set Cover problem in the distributed setting. This allows us to achieve an (f+epsilon)-approximate integral solution in O((1+f/log n)* ((log Delta)/(log log Delta) + (f * log M)^{1.01}* log epsilon^{-1}* (log Delta)^{0.01})) rounds, where f bounds the number of variables in a constraint, Delta bounds the number of constraints a variable appears in, and M=max {1, ceil[1/a_{min}]}, where a_{min} is the smallest normalized constraint coefficient. This improves over the results of [Fabian Kuhn et al., 2006] for the integral case, which combined with rounding achieves the same guarantees in O(epsilon^{-4}* f^4 * log f * log(M * Delta)) rounds.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.5/LIPIcs.DISC.2019.5.pdf
Distributed Algorithms
Approximation Algorithms
Vertex Cover
Set Cover
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
6:1
6:16
10.4230/LIPIcs.DISC.2019.6
article
Parameterized Distributed Algorithms
Ben-Basat, Ran
1
https://orcid.org/0000-0003-0196-9190
Kawarabayashi, Ken-ichi
2
https://orcid.org/0000-0001-6056-4287
Schwartzman, Gregory
2
https://orcid.org/0000-0002-8461-1479
Harvard University, Cambridge, MA, United States
National Institute of Informatics, Tokyo, Japan
In this work, we initiate a thorough study of graph optimization problems parameterized by the output size in the distributed setting. In such a problem, an algorithm decides whether a solution of size bounded by k exists and if so, it finds one. We study fundamental problems, including Minimum Vertex Cover (MVC), Maximum Independent Set (MaxIS), Maximum Matching (MaxM), and many others, in both the LOCAL and CONGEST distributed computation models. We present lower bounds for the round complexity of solving parameterized problems in both models, together with optimal and near-optimal upper bounds.
Our results extend beyond the scope of parameterized problems. We show that any LOCAL (1+epsilon)-approximation algorithm for the above problems must take Omega(epsilon^{-1}) rounds. Joined with the (epsilon^{-1}log n)^{O(1)} rounds algorithm of [Ghaffari et al., 2017] and the Omega (sqrt{(log n)/(log log n)}) lower bound of [Fabian Kuhn et al., 2016], the lower bounds match the upper bound up to polynomial factors in both parameters. We also show that our parameterized approach reduces the runtime of exact and approximate CONGEST algorithms for MVC and MaxM if the optimal solution is small, without knowing its size beforehand. Finally, we propose the first o(n^2) rounds CONGEST algorithms that approximate MVC within a factor strictly smaller than 2.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.6/LIPIcs.DISC.2019.6.pdf
Distributed Algorithms
Approximation Algorithms
Parameterized Algorithms
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
7:1
7:15
10.4230/LIPIcs.DISC.2019.7
article
Message Reduction in the LOCAL Model Is a Free Lunch
Bitton, Shimon
1
Emek, Yuval
1
Izumi, Taisuke
2
Kutten, Shay
1
Technion - Israel Institute of Technology, Haifa, Israel
Nagoya Institute of Technology, Japan
A new spanner construction algorithm is presented, working under the LOCAL model with unique edge IDs. Given an n-node communication graph, a spanner with a constant stretch and O(n^{1 + epsilon}) edges (for an arbitrarily small constant epsilon > 0) is constructed in a constant number of rounds sending O(n^{1 + epsilon}) messages whp. Consequently, we conclude that every t-round LOCAL algorithm can be transformed into an O(t)-round LOCAL algorithm that sends O(t * n^{1 + epsilon}) messages whp. This improves upon all previous message-reduction schemes for LOCAL algorithms that incur a log^{Omega (1)} n blow-up of the round complexity.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.7/LIPIcs.DISC.2019.7.pdf
distributed graph algorithms
spanner
LOCAL model
message complexity
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
8:1
8:17
10.4230/LIPIcs.DISC.2019.8
article
On the Computational Power of Radio Channels
Braverman, Mark
1
Kol, Gillat
1
Oshman, Rotem
2
Tal, Avishay
3
Princeton University, Princeton, NJ, USA
Tel Aviv University, Israel
UC Berkeley, CA, USA
Radio networks can be a challenging platform for which to develop distributed algorithms, because the network nodes must contend for a shared channel. In some cases, though, the shared medium is an advantage rather than a disadvantage: for example, many radio network algorithms cleverly use the shared channel to approximate the degree of a node, or estimate the contention. In this paper we ask how far the inherent power of a shared radio channel goes, and whether it can efficiently compute "classicaly hard" functions such as Majority, Approximate Sum, and Parity.
Using techniques from circuit complexity, we show that in many cases, the answer is "no". We show that simple radio channels, such as the beeping model or the channel with collision-detection, can be approximated by a low-degree polynomial, which makes them subject to known lower bounds on functions such as Parity and Majority; we obtain round lower bounds of the form Omega(n^{delta}) on these functions, for delta in (0,1). Next, we use the technique of random restrictions, used to prove AC^0 lower bounds, to prove a tight lower bound of Omega(1/epsilon^2) on computing a (1 +/- epsilon)-approximation to the sum of the nodes' inputs. Our techniques are general, and apply to many types of radio channels studied in the literature.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.8/LIPIcs.DISC.2019.8.pdf
radio channel
lower bounds
approximate majority
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
9:1
9:16
10.4230/LIPIcs.DISC.2019.9
article
Space-Optimal Naming in Population Protocols
Burman, Janna
1
Beauquier, Joffroy
1
Sohier, Devan
2
LRI, Université Paris-Sud, CNRS, Université Paris-Saclay, France
LI-PaRAD, Université de Versailles, Université Paris-Saclay, France
The distributed naming problem, assigning unique names to the nodes in a distributed system, is a fundamental task. This problem is nontrivial, especially when the amount of memory available for the task is low, and when requirements for fault-tolerance are added.
The considered distributed communication model is population protocols. In this model, a priori anonymous and indistinguishable mobile nodes (called agents), communicate in pairs and in an asynchronous manner (according to a fairness condition). Fault-tolerance is addressed through self-stabilization, in terms of arbitrary initialization of agents.
This work comprises a comprehensive study of the necessary and sufficient state space conditions for naming. The problem is studied under various combinations of model assumptions: weak or global fairness, arbitrary or uniform initialization of agents, existence or absence of a distinguishable agent (arbitrarily initialized or not), possibility of breaking symmetry in pair-wise interactions (symmetric or asymmetric transitions). For each possible combination of these assumptions, either an impossibility is proven or the necessary exact number of states (per mobile agent) is determined and an appropriate space-optimal naming protocol is presented.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.9/LIPIcs.DISC.2019.9.pdf
networks of passively mobile agents
population protocols
deterministic naming
self-stabilization
exact space complexity
tight lower bounds
global and weak fairness
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
10:1
10:17
10.4230/LIPIcs.DISC.2019.10
article
Erasure Correction for Noisy Radio Networks
Censor-Hillel, Keren
1
https://orcid.org/0000-0003-4395-5205
Haeupler, Bernhard
2
https://orcid.org/0000-0003-3381-0459
Hershkowitz, D. Ellis
2
https://orcid.org/0000-0003-0862-3715
Zuzic, Goran
2
https://orcid.org/0000-0002-9322-6329
Technion, Haifa, Israel
Computer Science Department, Carnegie Mellon University, Pittsburgh, PA, USA
The radio network model is a well-studied model of wireless, multi-hop networks. However, radio networks make the strong assumption that messages are delivered deterministically. The recently introduced noisy radio network model relaxes this assumption by dropping messages independently at random.
In this work we quantify the relative computational power of noisy radio networks and classic radio networks. In particular, given a non-adaptive protocol for a fixed radio network we show how to reliably simulate this protocol if noise is introduced with a multiplicative cost of poly(log Delta, log log n) rounds where n is the number nodes in the network and Delta is the max degree. Moreover, we demonstrate that, even if the simulated protocol is not non-adaptive, it can be simulated with a multiplicative O(Delta log ^2 Delta) cost in the number of rounds. Lastly, we argue that simulations with a multiplicative overhead of o(log Delta) are unlikely to exist by proving that an Omega(log Delta) multiplicative round overhead is necessary under certain natural assumptions.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.10/LIPIcs.DISC.2019.10.pdf
radio networks
erasure correction
noisy radio networks
protocol simulation
distributed computing models
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
11:1
11:13
10.4230/LIPIcs.DISC.2019.11
article
Reachability and Shortest Paths in the Broadcast CONGEST Model
Chechik, Shiri
1
Mukhtar, Doron
1
Tel Aviv University, Israel
In this paper we study the time complexity of the single-source reachability problem and the single-source shortest path problem for directed unweighted graphs in the Broadcast CONGEST model. We focus on the case where the diameter D of the underlying network is constant.
We show that for the case where D = 1 there is, quite surprisingly, a very simple algorithm that solves the reachability problem in 1(!) round. In contrast, for networks with D = 2, we show that any distributed algorithm (possibly randomized) for this problem requires Omega(sqrt{n/ log{n}}) rounds. Our results therefore completely resolve (up to a small polylog factor) the complexity of the single-source reachability problem for a wide range of diameters.
Furthermore, we show that when D = 1, it is even possible to get an almost 3 - approximation for the all-pairs shortest path problem (for directed unweighted graphs) in just 2 rounds. We also prove a stronger lower bound of Omega(sqrt{n}) for the single-source shortest path problem for unweighted directed graphs that holds even when the diameter of the underlying network is 2. As far as we know this is the first lower bound that achieves Omega(sqrt{n}) for this problem.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.11/LIPIcs.DISC.2019.11.pdf
Distributed algorithms
Broadcast CONGEST
distance estimation
small diameter
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
12:1
12:17
10.4230/LIPIcs.DISC.2019.12
article
On the Round Complexity of Randomized Byzantine Agreement
Cohen, Ran
1
2
Haitner, Iftach
3
Makriyannis, Nikolaos
4
Orland, Matan
3
Samorodnitsky, Alex
5
Boston University, MA, USA
Northeastern University, Boston, MA, USA
School of Computer Science, Tel Aviv University, Israel
Department of Computer Science, Technion, Haifa, Israel
School of Engineering and Computer Science, The Hebrew University of Jerusalem, Israel
We prove lower bounds on the round complexity of randomized Byzantine agreement (BA) protocols, bounding the halting probability of such protocols after one and two rounds. In particular, we prove that:
1) BA protocols resilient against n/3 [resp., n/4] corruptions terminate (under attack) at the end of the first round with probability at most o(1) [resp., 1/2+ o(1)].
2) BA protocols resilient against n/4 corruptions terminate at the end of the second round with probability at most 1-Theta(1).
3) For a large class of protocols (including all BA protocols used in practice) and under a plausible combinatorial conjecture, BA protocols resilient against n/3 [resp., n/4] corruptions terminate at the end of the second round with probability at most o(1) [resp., 1/2 + o(1)].
The above bounds hold even when the parties use a trusted setup phase, e.g., a public-key infrastructure (PKI).
The third bound essentially matches the recent protocol of Micali (ITCS'17) that tolerates up to n/3 corruptions and terminates at the end of the third round with constant probability.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.12/LIPIcs.DISC.2019.12.pdf
Byzantine agreement
lower bound
round complexity
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
13:1
13:17
10.4230/LIPIcs.DISC.2019.13
article
Trade-Offs in Distributed Interactive Proofs
Crescenzi, Pierluigi
1
Fraigniaud, Pierre
1
Paz, Ami
1
2
IRIF - CNRS and Université de Paris, France
Faculty of Computer Science, University of Vienna, Austria
The study of interactive proofs in the context of distributed network computing is a novel topic, recently introduced by Kol, Oshman, and Saxena [PODC 2018]. In the spirit of sequential interactive proofs theory, we study the power of distributed interactive proofs. This is achieved via a series of results establishing trade-offs between various parameters impacting the power of interactive proofs, including the number of interactions, the certificate size, the communication complexity, and the form of randomness used. Our results also connect distributed interactive proofs with the established field of distributed verification. In general, our results contribute to providing structure to the landscape of distributed interactive proofs.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.13/LIPIcs.DISC.2019.13.pdf
Distributed interactive proofs
Distributed verification
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
14:1
14:17
10.4230/LIPIcs.DISC.2019.14
article
The Capacity of Smartphone Peer-To-Peer Networks
Dinitz, Michael
1
Halldórsson, Magnús M.
2
Newport, Calvin
3
Weaver, Alex
3
Johns Hopkins University, Baltimore, MD, United States
Reykjavík University, Iceland
Georgetown University, Washington, DC, United States
We study three capacity problems in the mobile telephone model, a network abstraction that models the peer-to-peer communication capabilities implemented in most commodity smartphone operating systems. The capacity of a network expresses how much sustained throughput can be maintained for a set of communication demands, and is therefore a fundamental bound on the usefulness of a network. Because of this importance, wireless network capacity has been active area of research for the last two decades.
The three capacity problems that we study differ in the structure of the communication demands. The first problem is pairwise capacity, where the demands are (source, destination) pairs. Pairwise capacity is one of the most classical definitions, as it was analyzed in the seminal paper of Gupta and Kumar on wireless network capacity. The second problem we study is broadcast capacity, in which a single source must deliver packets to all other nodes in the network. Finally, we turn our attention to all-to-all capacity, in which all nodes must deliver packets to all other nodes. In all three of these problems we characterize the optimal achievable throughput for any given network, and design algorithms which asymptotically match this performance. We also study these problems in networks generated randomly by a process introduced by Gupta and Kumar, and fully characterize their achievable throughput.
Interestingly, the techniques that we develop for all-to-all capacity also allow us to design a one-shot gossip algorithm that runs within a polylogarithmic factor of optimal in every graph. This largely resolves an open question from previous work on the one-shot gossip problem in this model.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.14/LIPIcs.DISC.2019.14.pdf
Capacity
Wireless
Mobile Telephone
Throughput
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
15:1
15:16
10.4230/LIPIcs.DISC.2019.15
article
Sublinear-Time Distributed Algorithms for Detecting Small Cliques and Even Cycles
Eden, Talya
1
Fiat, Nimrod
2
Fischer, Orr
2
Kuhn, Fabian
3
Oshman, Rotem
2
Electrical Engineering Department, Tel-Aviv University, Israel
Computer Science Department, Tel-Aviv University, Israel
Computer Science Department, University of Freiburg, Germany
In this paper we give sublinear-time distributed algorithms in the CONGEST model for subgraph detection for two classes of graphs: cliques and even-length cycles. We show for the first time that all copies of 4-cliques and 5-cliques in the network graph can be listed in sublinear time, O(n^{5/6+o(1)}) rounds and O(n^{21/22+o(1)}) rounds, respectively. Prior to our work, it was not known whether it was possible to even check if the network contains a 4-clique or a 5-clique in sublinear time.
For even-length cycles, C_{2k}, we give an improved sublinear-time algorithm, which exploits a new connection to extremal combinatorics. For example, for 6-cycles we improve the running time from O~(n^{5/6}) to O~(n^{3/4}) rounds. We also show two obstacles on proving lower bounds for C_{2k}-freeness: First, we use the new connection to extremal combinatorics to show that the current lower bound of Omega~(sqrt{n}) rounds for 6-cycle freeness cannot be improved using partition-based reductions from 2-party communication complexity, the technique by which all known lower bounds on subgraph detection have been proven to date. Second, we show that there is some fixed constant delta in (0,1/2) such that for any k, a Omega(n^{1/2+delta}) lower bound on C_{2k}-freeness implies new lower bounds in circuit complexity.
For general subgraphs, it was shown in [Orr Fischer et al., 2018] that for any fixed k, there exists a subgraph H of size k such that H-freeness requires Omega~(n^{2-Theta(1/k)}) rounds. It was left as an open problem whether this is tight, or whether some constant-sized subgraph requires truly quadratic time to detect. We show that in fact, for any subgraph H of constant size k, the H-freeness problem can be solved in O(n^{2 - Theta(1/k)}) rounds, nearly matching the lower bound of [Orr Fischer et al., 2018].
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.15/LIPIcs.DISC.2019.15.pdf
Distributed Computing
Subgraph Freeness
CONGEST
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
16:1
16:16
10.4230/LIPIcs.DISC.2019.16
article
A Distributed Algorithm for Directed Minimum-Weight Spanning Tree
Fischer, Orr
1
Oshman, Rotem
1
Computer Science Department, Tel-Aviv University, Israel
In the directed minimum spanning tree problem (DMST, also called minimum weight arborescence), the network is given a root node r, and needs to construct a minimum-weight directed spanning tree, rooted at r and oriented outwards. In this paper we present the first sub-quadratic DMST algorithms in the distributed CONGEST network model, where the messages exchanged between the network nodes are bounded in size. We consider three versions: a model where the communication links are bidirectional but can have different weights in the two directions; a model where communication is unidirectional; and the Congested Clique model, where all nodes can communicate directly with each other.
Our algorithm is based on a variant of Lovász' DMST algorithm for the PRAM model, and uses a distributed single-source shortest-path (SSSP) algorithm for directed graphs as a black box. In the bidirectional CONGEST model, our algorithm has roughly the same running time as the SSSP algorithm; using the state-of-the-art SSSP algorithm, we obtain a running time of O~(min(sqrt{nD},sqrt{n}D^{1/4} + n^{3/5} +D)) rounds for the bidirectional communication case.
For the unidirectional communication model we give an O~(n) algorithm, and show that it is nearly optimal. And finally, for the Congested Clique, our algorithm again matches the best known SSSP algorithm: it runs in O~(n^{1/3}) rounds.
On the negative side, we adapt an observation of Chechik in the sequential setting to show that in all three models, the DMST problem is at least as hard as the (s,t)-shortest path problem. Thus, in terms of round complexity, distributed DMST lies between single-source shortest path and (s,t)-shortest path.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.16/LIPIcs.DISC.2019.16.pdf
Distributed Computing
Directed Minimum Spanning Tree
Minimum Arborescence
CONGEST
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
17:1
17:16
10.4230/LIPIcs.DISC.2019.17
article
Stable Memoryless Queuing under Contention
Garncarek, Paweł
1
https://orcid.org/0000-0002-6855-0530
Jurdziński, Tomasz
1
https://orcid.org/0000-0003-1908-9458
Kowalski, Dariusz R.
2
3
Institute of Computer Science, University of Wroclaw, Poland
School of Computer and Cyber Sciences, Augusta University, Augusta, USA
SWPS University of Social Sciences and Humanities, Warsaw, Poland
In this work we study stability of local memoryless packet scheduling policies in a distributed system of n nodes/queues under contention. The local policies at nodes may only access their current local queues, and have no other feedback from the underlying distributed system. Moreover, their memory is limited to some basic parameters. The packets arrive at queues according to arrival patterns controlled by an adversary restricted only by injection rate rho and burstiness b, or driven by a stochastic process; the former model analyzes worst-case stability while the latter - average case. We assume that the underlying distributed system is a classic shared channel, in which no two packets could be successfully scheduled (and removed from queues) at the same time. We show that there is a local memoryless scheduling policy which is both adversarially and stochastically stable for injection rates Omega(1/log n). Another algorithm achieves even higher - constant - stable injection rate, but only for a bounded range of burstiness. The first algorithm is utilizing properties of interleaved ultra-selectors, for which we prove stronger properties than known so far, while the second one is based on entirely new concept of selector with thresholds, unlike previously considered binary selectors/codes in the literature.
Note that popular Backoff algorithms, some of which achieve stability for constant (stochastic) injection rates [Johan Håstad et al., 1996], use memory to record current state (e.g., the number of unsuccessful transmissions or the result of random sampling in each window) as well as randomization and feedback from the channel; unlike solutions in this work, which are memoryless and do not rely on randomization or channel feedback (thus, could be used independently from the link layer protocols). {}
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.17/LIPIcs.DISC.2019.17.pdf
packet scheduling
online algorithms
adversarial injections
stochastic injections
stability
memoryless algorithms
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
18:1
18:16
10.4230/LIPIcs.DISC.2019.18
article
Improved Network Decompositions Using Small Messages with Applications on MIS, Neighborhood Covers, and Beyond
Ghaffari, Mohsen
1
Portmann, Julian
2
ETH Zurich, Switzerland
ETH Zürich, Switzerland
Network decompositions, as introduced by Awerbuch, Luby, Goldberg, and Plotkin [FOCS'89], are one of the key algorithmic tools in distributed graph algorithms. We present an improved deterministic distributed algorithm for constructing network decompositions of power graphs using small messages, which improves upon the algorithm of Ghaffari and Kuhn [DISC'18]. In addition, we provide a randomized distributed network decomposition algorithm, based on our deterministic algorithm, with failure probability exponentially small in the input size that works with small messages as well. Compared to the previous algorithm of Elkin and Neiman [PODC'16], our algorithm achieves a better success probability at the expense of its round complexity, while giving a network decomposition of the same quality. As a consequence of the randomized algorithm for network decomposition, we get a faster randomized algorithm for computing a Maximal Independent Set, improving on a result of Ghaffari [SODA'19]. Other implications of our improved deterministic network decomposition algorithm are: a faster deterministic distributed algorithms for constructing spanners and approximations of distributed set cover, improving results of Ghaffari, and Kuhn [DISC'18] and Deurer, Kuhn, and Maus [PODC'19]; and faster a deterministic distributed algorithm for constructing neighborhood covers, resolving an open question of Elkin [SODA'04].
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.18/LIPIcs.DISC.2019.18.pdf
Distributed Graph Algorithms
Network Decomposition
Maximal Independent Set
Neighborhood Cover
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
19:1
19:17
10.4230/LIPIcs.DISC.2019.19
article
On Bioelectric Algorithms
Gilbert, Seth
1
Maguire, James
2
Newport, Calvin
2
National University of Singapore, Singapore
Georgetown University, Washington, DC, USA
Cellular bioelectricity describes the biological phenomenon in which cells in living tissue generate and maintain patterns of voltage gradients across their membranes induced by differing concentrations of charged ions. A growing body of research suggests that bioelectric patterns represent an ancient system that plays a key role in guiding many important developmental processes including tissue regeneration, tumor suppression, and embryogenesis. This paper applies techniques from distributed algorithm theory to help better understand how cells work together to form these patterns. To do so, we present the cellular bioelectric model (CBM), a new computational model that captures the primary capabilities and constraints of bioelectric interactions between cells and their environment. We use this model to investigate several important topics from the relevant biology research literature. We begin with symmetry breaking, analyzing a simple cell definition that when combined in single hop or multihop topologies, efficiently solves leader election and the maximal independent set problem, respectively - indicating that these classical symmetry breaking tasks are well-matched to bioelectric mechanisms. We then turn our attention to the information processing ability of bioelectric cells, exploring upper and lower bounds for approximate solutions to threshold and majority detection, and then proving that these systems are in fact Turing complete - resolving an open question about the computational power of bioelectric interactions.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.19/LIPIcs.DISC.2019.19.pdf
biological distributed algorithms
bioelectric networks
natural algorithms
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
20:1
20:18
10.4230/LIPIcs.DISC.2019.20
article
Parallel Finger Search Structures
Gilbert, Seth
1
Lim, Wei Quan
1
Computer Science, National University of Singapore
In this paper we present two versions of a parallel finger structure FS on p processors that supports searches, insertions and deletions, and has a finger at each end. This is to our knowledge the first implementation of a parallel search structure that is work-optimal with respect to the finger bound and yet has very good parallelism (within a factor of O(log p)^2) of optimal). We utilize an extended implicit batching framework that transparently facilitates the use of FS by any parallel program P that is modelled by a dynamically generated DAG D where each node is either a unit-time instruction or a call to FS.
The work done by FS is bounded by the finger bound F_L (for some linearization L of D), i.e. each operation on an item with distance r from a finger takes O(log r+1) amortized work. Running P using the simpler version takes O((T_1+F_L)/p + T_infty + d * ((log p)^2 + log n)) time on a greedy scheduler, where T_1, T_infty are the size and span of D respectively, and n is the maximum number of items in FS, and d is the maximum number of calls to FS along any path in D. Using the faster version, this is reduced to O((T_1+F_L)/p + T_infty + d *(log p)^2 + s_L) time, where s_L is the weighted span of D where each call to FS is weighted by its cost according to F_L. FS can be extended to a fixed number of movable fingers.
The data structures in our paper fit into the dynamic multithreading paradigm, and their performance bounds are directly composable with other data structures given in the same paradigm. Also, the results can be translated to practical implementations using work-stealing schedulers.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.20/LIPIcs.DISC.2019.20.pdf
Parallel data structures
Multithreading
Dictionaries
Comparison-based Search
Distribution-sensitive algorithms
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
21:1
21:16
10.4230/LIPIcs.DISC.2019.21
article
Wait-Free Solvability of Equality Negation Tasks
Goubault, Éric
1
Lazić, Marijana
2
Ledent, Jérémy
1
Rajsbaum, Sergio
3
École Polytechnique, Palaiseau, France
TU München, Munich, Germany
Instituto de Matemáticas, UNAM, Mexico City, Mexico
We introduce a family of tasks for n processes, as a generalization of the two process equality negation task of Lo and Hadzilacos (SICOMP 2000). Each process starts the computation with a private input value taken from a finite set of possible inputs. After communicating with the other processes using immediate snapshots, the process must decide on a binary output value, 0 or 1. The specification of the task is the following: in an execution, if the set of input values is large enough, the processes should agree on the same output; if the set of inputs is small enough, the processes should disagree; and in-between these two cases, any output is allowed. Formally, this specification depends on two threshold parameters k and l, with k<l, indicating when the cardinality of the set of inputs becomes "small" or "large", respectively. We study the solvability of this task depending on those two parameters. First, we show that the task is solvable whenever k+2 <= l. For the remaining cases (l = k+1), we use various combinatorial topology techniques to obtain two impossibility results: the task is unsolvable if either k <= n/2 or n-k is odd. The remaining cases are still open.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.21/LIPIcs.DISC.2019.21.pdf
Equality negation
distributed computability
combinatorial topology
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
22:1
22:16
10.4230/LIPIcs.DISC.2019.22
article
Scalable Byzantine Reliable Broadcast
Guerraoui, Rachid
1
Kuznetsov, Petr
2
Monti, Matteo
1
Pavlovic, Matej
1
Seredinschi, Dragos-Adrian
1
EPFL, Lausanne, Switzerland
LTCI, Télécom Paris, IP Paris, Paris, France
Byzantine reliable broadcast is a powerful primitive that allows a set of processes to agree on a message from a designated sender, even if some processes (including the sender) are Byzantine. Existing broadcast protocols for this setting scale poorly, as they typically build on quorum systems with strong intersection guarantees, which results in linear per-process communication and computation complexity.
We generalize the Byzantine reliable broadcast abstraction to the probabilistic setting, allowing each of its properties to be violated with a fixed, arbitrarily small probability. We leverage these relaxed guarantees in a protocol where we replace quorums with stochastic samples. Compared to quorums, samples are significantly smaller in size, leading to a more scalable design. We obtain the first Byzantine reliable broadcast protocol with logarithmic per-process communication and computation complexity.
We conduct a complete and thorough analysis of our protocol, deriving bounds on the probability of each of its properties being compromised. During our analysis, we introduce a novel general technique that we call adversary decorators. Adversary decorators allow us to make claims about the optimal strategy of the Byzantine adversary without imposing any additional assumptions. We also introduce Threshold Contagion, a model of message propagation through a system with Byzantine processes. To the best of our knowledge, this is the first formal analysis of a probabilistic broadcast protocol in the Byzantine fault model. We show numerically that practically negligible failure probabilities can be achieved with realistic security parameters.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.22/LIPIcs.DISC.2019.22.pdf
Byzantine reliable broadcast
probabilistic distributed algorithms
scalable distributed systems
stochastic processes
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
23:1
23:16
10.4230/LIPIcs.DISC.2019.23
article
Fast Distributed Algorithms for LP-Type Problems of Low Dimension
Hinnenthal, Kristian
1
Scheideler, Christian
1
Struijs, Martijn
2
Paderborn University, Germany
TU Eindhoven, The Netherlands
In this paper we present various distributed algorithms for LP-type problems in the well-known gossip model. LP-type problems include many important classes of problems such as (integer) linear programming, geometric problems like smallest enclosing ball and polytope distance, and set problems like hitting set and set cover. In the gossip model, a node can only push information to or pull information from nodes chosen uniformly at random. Protocols for the gossip model are usually very practical due to their fast convergence, their simplicity, and their stability under stress and disruptions. Our algorithms are very efficient (logarithmic rounds or better with just polylogarithmic communication work per node per round) whenever the combinatorial dimension of the given LP-type problem is constant, even if the size of the given LP-type problem is polynomially large in the number of nodes.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.23/LIPIcs.DISC.2019.23.pdf
LP-type problems
linear optimization
distributed algorithms
gossip algorithms
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
24:1
24:17
10.4230/LIPIcs.DISC.2019.24
article
Privatization-Safe Transactional Memories
Khyzha, Artem
1
Attiya, Hagit
2
Gotsman, Alexey
3
Tel Aviv University, Tel Aviv, Israel
Technion - Israel Institute of Technology, Haifa, Israel
IMDEA Software Institute, Madrid, Spain
Transactional memory (TM) facilitates the development of concurrent applications by letting the programmer designate certain code blocks as atomic. Programmers using a TM often would like to access the same data both inside and outside transactions, and would prefer their programs to have a strongly atomic semantics, which allows transactions to be viewed as executing atomically with respect to non-transactional accesses. Since guaranteeing such semantics for arbitrary programs is prohibitively expensive, researchers have suggested guaranteeing it only for certain data-race free (DRF) programs, particularly those that follow the privatization idiom: from some point on, threads agree that a given object can be accessed non-transactionally.
In this paper we show that a variant of Transactional DRF (TDRF) by Dalessandro et al. is appropriate for a class of privatization-safe TMs, which allow using privatization idioms. We prove that, if such a TM satisfies a condition we call privatization-safe opacity and a program using the TM is TDRF under strongly atomic semantics, then the program indeed has such semantics. We also present a method for proving privatization-safe opacity that reduces proving this generalization to proving the usual opacity, and apply the method to a TM based on two-phase locking and a privatization-safe version of TL2. Finally, we establish the inherent cost of privatization-safety: we prove that a TM cannot be progressive and have invisible reads if it guarantees strongly atomic semantics for TDRF programs.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.24/LIPIcs.DISC.2019.24.pdf
Transactional memory
privatization
observational refinement
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
25:1
25:17
10.4230/LIPIcs.DISC.2019.25
article
Low-Congestion Shortcut and Graph Parameters
Kitamura, Naoki
1
Kitagawa, Hirotaka
1
Otachi, Yota
2
Izumi, Taisuke
1
Nagoya Institute of Technology, Japan
Kumamoto University, Japan
Distributed graph algorithms in the standard CONGEST model often exhibit the time-complexity lower bound of Omega~(sqrt{n} + D) rounds for many global problems, where n is the number of nodes and D is the diameter of the input graph. Since such a lower bound is derived from special "hard-core" instances, it does not necessarily apply to specific popular graph classes such as planar graphs. The concept of low-congestion shortcuts is initiated by Ghaffari and Haeupler [SODA2016] for addressing the design of CONGEST algorithms running fast in restricted network topologies. Specifically, given a specific graph class X, an f-round algorithm of constructing shortcuts of quality q for any instance in X results in O~(q + f)-round algorithms of solving several fundamental graph problems such as minimum spanning tree and minimum cut, for X. The main interest on this line is to identify the graph classes allowing the shortcuts which are efficient in the sense of breaking O~(sqrt{n}+D)-round general lower bounds.
In this paper, we consider the relationship between the quality of low-congestion shortcuts and three major graph parameters, chordality, diameter, and clique-width. The main contribution of the paper is threefold: (1) We show an O(1)-round algorithm which constructs a low-congestion shortcut with quality O(kD) for any k-chordal graph, and prove that the quality and running time of this construction is nearly optimal up to polylogarithmic factors. (2) We present two algorithms, each of which constructs a low-congestion shortcut with quality O~(n^{1/4}) in O~(n^{1/4}) rounds for graphs of D=3, and that with quality O~(n^{1/3}) in O~(n^{1/3}) rounds for graphs of D=4 respectively. These results obviously deduce two MST algorithms running in O~(n^{1/4}) and O~(n^{1/3}) rounds for D=3 and 4 respectively, which almost close the long-standing complexity gap of the MST construction in small-diameter graphs originally posed by Lotker et al. [Distributed Computing 2006]. (3) We show that bounding clique-width does not help the construction of good shortcuts by presenting a network topology of clique-width six where the construction of MST is as expensive as the general case.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.25/LIPIcs.DISC.2019.25.pdf
distributed graph algorithms
low-congestion shortcut
k-chordal graph
clique width
minimum spanning tree
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
26:1
26:18
10.4230/LIPIcs.DISC.2019.26
article
The Complexity of Symmetry Breaking in Massive Graphs
Konrad, Christian
1
Pemmaraju, Sriram V.
2
Riaz, Talal
2
Robinson, Peter
3
Department of Computer Science, University of Bristol, Bristol BS8 1UB, UK
Department of Computer Science, The University of Iowa, Iowa City, IA 52242, USA
Department of Computer Science, City University of Hong Kong
The goal of this paper is to understand the complexity of symmetry breaking problems, specifically maximal independent set (MIS) and the closely related beta-ruling set problem, in two computational models suited for large-scale graph processing, namely the k-machine model and the graph streaming model. We present a number of results. For MIS in the k-machine model, we improve the O~(m/k^2 + Delta/k)-round upper bound of Klauck et al. (SODA 2015) by presenting an O~(m/k^2)-round algorithm. We also present an Omega~(n/k^2) round lower bound for MIS, the first lower bound for a symmetry breaking problem in the k-machine model. For beta-ruling sets, we use hierarchical sampling to obtain more efficient algorithms in the k-machine model and also in the graph streaming model. More specifically, we obtain a k-machine algorithm that runs in O~(beta n Delta^{1/beta}/k^2) rounds and, by using a similar hierarchical sampling technique, we obtain one-pass algorithms for both insertion-only and insertion-deletion streams that use O(beta * n^{1+1/2^{beta-1}}) space. The latter result establishes a clear separation between MIS, which is known to require Omega(n^2) space (Cormode et al., ICALP 2019), and beta-ruling sets, even for beta = 2. Finally, we present an even faster 2-ruling set algorithm in the k-machine model, one that runs in O~(n/k^{2-epsilon} + k^{1-epsilon}) rounds for any epsilon, 0 <=epsilon <=1. For a wide range of values of k this round complexity simplifies to O~(n/k^2) rounds, which we conjecture is optimal.
Our results use a variety of techniques. For our upper bounds, we prove and use simulation theorems for beeping algorithms, hierarchical sampling, and L_0-sampling, whereas for our lower bounds we use information-theoretic arguments and reductions to 2-party communication complexity problems.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.26/LIPIcs.DISC.2019.26.pdf
communication complexity
information theory
k-machine model
maximal independent set
ruling set
streaming algorithms
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
27:1
27:15
10.4230/LIPIcs.DISC.2019.27
article
Stellar Consensus by Instantiation
Losa, Giuliano
1
Gafni, Eli
2
Mazières, David
3
Galois, Inc., Portland, OR, USA
UCLA, Los Angeles, CA, USA
Stanford University, CA, USA
Stellar introduced a new type of quorum system called a Federated Byzantine Agreement System. A major difference between this novel type of quorum system and a threshold quorum system is that each participant has its own, personal notion of a quorum. Thus, unlike in a traditional BFT system, designed for a uniform notion of quorum, even in a time of synchrony one well-behaved participant may observe a quorum of well-behaved participants, while others may not.
To tackle this new problem in a more general setting, we abstract the Stellar Network as an instance of what we call Personal Byzantine Quorum Systems. Using this notion, we streamline the theory behind the Stellar Network, removing the clutter of unnecessary details, and refute the conjecture that Stellar’s notion of intact set is optimally fault-tolerant. Most importantly, we develop a new consensus algorithm for the new setting.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.27/LIPIcs.DISC.2019.27.pdf
Consensus
Stellar
Partial Synchrony
Byzantine Fault Tolerance
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
28:1
28:16
10.4230/LIPIcs.DISC.2019.28
article
A Scalable, Portable, and Memory-Efficient Lock-Free FIFO Queue
Nikolaev, Ruslan
1
Virginia Tech, Blacksburg, VA, USA
We present a new lock-free multiple-producer and multiple-consumer (MPMC) FIFO queue design which is scalable and, unlike existing high-performant queues, very memory efficient. Moreover, the design is ABA safe and does not require any external memory allocators or safe memory reclamation techniques, typically needed by other scalable designs. In fact, this queue itself can be leveraged for object allocation and reclamation, as in data pools. We use FAA (fetch-and-add), a specialized and more scalable than CAS (compare-and-set) instruction, on the most contended hot spots of the algorithm. However, unlike prior attempts with FAA, our queue is both lock-free and linearizable.
We propose a general approach, SCQ, for bounded queues. This approach can easily be extended to support unbounded FIFO queues which can store an arbitrary number of elements. SCQ is portable across virtually all existing architectures and flexible enough for a wide variety of uses. We measure the performance of our algorithm on the x86-64 and PowerPC architectures. Our evaluation validates that our queue has exceptional memory efficiency compared to other algorithms and its performance is often comparable to, or exceeding that of state-of-the-art scalable algorithms.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.28/LIPIcs.DISC.2019.28.pdf
FIFO
queue
ring buffer
lock-free
non-blocking
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
29:1
29:17
10.4230/LIPIcs.DISC.2019.29
article
Byzantine Approximate Agreement on Graphs
Nowak, Thomas
1
2
https://orcid.org/0000-0003-1690-9342
Rybicki, Joel
3
https://orcid.org/0000-0002-6432-6646
Université Paris-Sud, France
Centre National de la Recherche Scientifique, Paris, France
Institute of Science and Technology Austria, Klosterneuburg, Austria
Consider a distributed system with n processors out of which f can be Byzantine faulty. In the approximate agreement task, each processor i receives an input value x_i and has to decide on an output value y_i such that
1) the output values are in the convex hull of the non-faulty processors' input values,
2) the output values are within distance d of each other.
Classically, the values are assumed to be from an m-dimensional Euclidean space, where m >= 1.
In this work, we study the task in a discrete setting, where input values with some structure expressible as a graph. Namely, the input values are vertices of a finite graph G and the goal is to output vertices that are within distance d of each other in G, but still remain in the graph-induced convex hull of the input values. For d=0, the task reduces to consensus and cannot be solved with a deterministic algorithm in an asynchronous system even with a single crash fault. For any d >= 1, we show that the task is solvable in asynchronous systems when G is chordal and n > (omega+1)f, where omega is the clique number of G. In addition, we give the first Byzantine-tolerant algorithm for a variant of lattice agreement. For synchronous systems, we show tight resilience bounds for the exact variants of these and related tasks over a large class of combinatorial structures.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.29/LIPIcs.DISC.2019.29.pdf
consensus
approximate agreement
Byzantine faults
chordal graphs
lattice agreement
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
30:1
30:16
10.4230/LIPIcs.DISC.2019.30
article
Small Cuts and Connectivity Certificates: A Fault Tolerant Approach
Parter, Merav
1
Weizmann Institute, Rehovot, Israel
We revisit classical connectivity problems in the {CONGEST} model of distributed computing. By using techniques from fault tolerant network design, we show improved constructions, some of which are even "local" (i.e., with O~(1) rounds) for problems that are closely related to hard global problems (i.e., with a lower bound of Omega(Diam+sqrt{n}) rounds).
Distributed Minimum Cut: Nanongkai and Su presented a randomized algorithm for computing a (1+epsilon)-approximation of the minimum cut using O~(D +sqrt{n}) rounds where D is the diameter of the graph. For a sufficiently large minimum cut lambda=Omega(sqrt{n}), this is tight due to Das Sarma et al. [FOCS '11], Ghaffari and Kuhn [DISC '13].
- Small Cuts: A special setting that remains open is where the graph connectivity lambda is small (i.e., constant). The only lower bound for this case is Omega(D), with a matching bound known only for lambda <= 2 due to Pritchard and Thurimella [TALG '11]. Recently, Daga, Henzinger, Nanongkai and Saranurak [STOC '19] raised the open problem of computing the minimum cut in poly(D) rounds for any lambda=O(1). In this paper, we resolve this problem by presenting a surprisingly simple algorithm, that takes a completely different approach than the existing algorithms. Our algorithm has also the benefit that it computes all minimum cuts in the graph, and naturally extends to vertex cuts as well. At the heart of the algorithm is a graph sampling approach usually used in the context of fault tolerant (FT) design.
- Deterministic Algorithms: While the existing distributed minimum cut algorithms are randomized, our algorithm can be made deterministic within the same round complexity. To obtain this, we introduce a novel definition of universal sets along with their efficient computation. This allows us to derandomize the FT graph sampling technique, which might be of independent interest.
- Computation of all Edge Connectivities: We also consider the more general task of computing the edge connectivity of all the edges in the graph. In the output format, it is required that the endpoints u,v of every edge (u,v) learn the cardinality of the u-v cut in the graph. We provide the first sublinear algorithm for this problem for the case of constant connectivity values. Specifically, by using the recent notion of low-congestion cycle cover, combined with the sampling technique, we compute all edge connectivities in poly(D) * 2^{O(sqrt{log n log log n})} rounds.
Sparse Certificates: For an n-vertex graph G and an integer lambda, a lambda-sparse certificate H is a subgraph H subseteq G with O(lambda n) edges which is lambda-connected iff G is lambda-connected. For D-diameter graphs, constructions of sparse certificates for lambda in {2,3} have been provided by Thurimella [J. Alg. '97] and Dori [PODC '18] respectively using O~(D) number of rounds. The problem of devising such certificates with o(D+sqrt{n}) rounds was left open by Dori [PODC '18] for any lambda >= 4. Using connections to fault tolerant spanners, we considerably improve the round complexity for any lambda in [1,n] and epsilon in (0,1), by showing a construction of (1-epsilon)lambda-sparse certificates with O(lambda n) edges using only O(1/epsilon^2 * log^{2+o(1)} n) rounds.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.30/LIPIcs.DISC.2019.30.pdf
Connectivity
Minimum Cut
Spanners
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
31:1
31:15
10.4230/LIPIcs.DISC.2019.31
article
Monotonically Relaxing Concurrent Data-Structure Semantics for Increasing Performance: An Efficient 2D Design Framework
Rukundo, Adones
1
Atalar, Aras
1
Tsigas, Philippas
1
Chalmers University of Technology Department of Computer Science and Engineering, Sweden
There has been a significant amount of work in the literature proposing semantic relaxation of concurrent data structures for improving scalability and performance. By relaxing the semantics of a data structure, a bigger design space, that allows weaker synchronization and more useful parallelism, is unveiled. Investigating new data structure designs, capable of trading semantics for achieving better performance in a monotonic way, is a major challenge in the area. We algorithmically address this challenge in this paper.
We present an efficient, lock-free, concurrent data structure design framework for out-of-order semantic relaxation. We introduce a new two dimensional algorithmic design, that uses multiple instances of a given data structure. The first dimension of our design is the number of data structure instances operations are spread to, in order to benefit from parallelism through disjoint memory access; the second dimension is the number of consecutive operations that try to use the same data structure instance in order to benefit from data locality. Our design can flexibly explore this two-dimensional space to achieve the property of monotonically relaxing concurrent data structure semantics for better performance within a tight deterministic relaxation bound, as we prove in the paper.
We show how our framework can instantiate lock-free out-of-order queues, stacks, counters and dequeues. We provide implementations of these relaxed data structures and evaluate their performance and behaviour on two parallel architectures. Experimental evaluation shows that our two-dimensional design significantly outperforms the respected previous proposed designs with respect to scalability and performance. Moreover, our design increases performance monotonically as relaxation increases.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.31/LIPIcs.DISC.2019.31.pdf
Lock Free
Concurrency
Semantics Relaxation
Data Structures
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
32:1
32:17
10.4230/LIPIcs.DISC.2019.32
article
Phase Transitions of Best-of-Two and Best-of-Three on Stochastic Block Models
Shimizu, Nobutaka
1
Shiraga, Takeharu
2
The University of Tokyo, Japan
Chuo University, Tokyo, Japan
This paper is concerned with voting processes on graphs where each vertex holds one of two different opinions. In particular, we study the Best-of-two and the Best-of-three. Here at each synchronous and discrete time step, each vertex updates its opinion to match the majority among the opinions of two random neighbors and itself (the Best-of-two) or the opinions of three random neighbors (the Best-of-three). Previous studies have explored these processes on complete graphs and expander graphs, but we understand significantly less about their properties on graphs with more complicated structures.
In this paper, we study the Best-of-two and the Best-of-three on the stochastic block model G(2n,p,q), which is a random graph consisting of two distinct Erdős-Rényi graphs G(n,p) joined by random edges with density q <= p. We obtain two main results. First, if p=omega(log n/n) and r=q/p is a constant, we show that there is a phase transition in r with threshold r^* (specifically, r^*=sqrt{5}-2 for the Best-of-two, and r^*=1/7 for the Best-of-three). If r>r^*, the process reaches consensus within O(log log n+log n/log (np)) steps for any initial opinion configuration with a bias of Omega(n). By contrast, if r<r^*, then there exists an initial opinion configuration with a bias of Omega(n) from which the process requires at least 2^{Omega(n)} steps to reach consensus. Second, if p is a constant and r>r^*, we show that, for any initial opinion configuration, the process reaches consensus within O(log n) steps. To the best of our knowledge, this is the first result concerning multiple-choice voting for arbitrary initial opinion configurations on non-complete graphs.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.32/LIPIcs.DISC.2019.32.pdf
Distributed Voting
Consensus Problem
Random Graph
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
33:1
33:16
10.4230/LIPIcs.DISC.2019.33
article
Distributed Data Summarization in Well-Connected Networks
Su, Hsin-Hao
1
Vu, Hoa T.
1
Boston College, MA, USA
We study distributed algorithms for some fundamental problems in data summarization. Given a communication graph G of n nodes each of which may hold a value initially, we focus on computing sum_{i=1}^N g(f_i), where f_i is the number of occurrences of value i and g is some fixed function. This includes important statistics such as the number of distinct elements, frequency moments, and the empirical entropy of the data.
In the CONGEST~ model, a simple adaptation from streaming lower bounds shows that it requires Omega~(D+ n) rounds, where D is the diameter of the graph, to compute some of these statistics exactly. However, these lower bounds do not hold for graphs that are well-connected. We give an algorithm that computes sum_{i=1}^{N} g(f_i) exactly in {tau_{G}} * 2^{O(sqrt{log n})} rounds where {tau_{G}} is the mixing time of G. This also has applications in computing the top k most frequent elements.
We demonstrate that there is a high similarity between the GOSSIP~ model and the CONGEST~ model in well-connected graphs. In particular, we show that each round of the GOSSIP~ model can be simulated almost perfectly in O~({tau_{G}}) rounds of the CONGEST~ model. To this end, we develop a new algorithm for the GOSSIP~ model that 1 +/- epsilon approximates the p-th frequency moment F_p = sum_{i=1}^N f_i^p in O~(epsilon^{-2} n^{1-k/p}) rounds , for p >= 2, when the number of distinct elements F_0 is at most O(n^{1/(k-1)}). This result can be translated back to the CONGEST~ model with a factor O~({tau_{G}}) blow-up in the number of rounds.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.33/LIPIcs.DISC.2019.33.pdf
Distributed Algorithms
Network Algorithms
Data Summarization
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
34:1
34:17
10.4230/LIPIcs.DISC.2019.34
article
Polynomial-Time Fence Insertion for Structured Programs
Taheri, Mohammad
1
https://orcid.org/0000-0002-1251-6894
Pourdamghani, Arash
1
https://orcid.org/0000-0002-9213-1512
Lesani, Mohsen
2
Sharif University of Technology, Iran
University of California at Riverside, USA
To enhance performance, common processors feature relaxed memory models that reorder instructions. However, the correctness of concurrent programs is often dependent on the preservation of the program order of certain instructions. Thus, the instruction set architectures offer memory fences. Using fences is a subtle task with performance and correctness implications: using too few can compromise correctness and using too many can hinder performance. Thus, fence insertion algorithms that given the required program orders can automatically find the optimum fencing can enhance the ease of programming, reliability, and performance of concurrent programs. In this paper, we consider the class of programs with structured branch and loop statements and present a greedy and polynomial-time optimum fence insertion algorithm. The algorithm incrementally reduces fence insertion for a control-flow graph to fence insertion for a set of paths. In addition, we show that the minimum fence insertion problem with multiple types of fence instructions is NP-hard even for straight-line programs.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.34/LIPIcs.DISC.2019.34.pdf
Fence Insertion
Synchronization
Concurrent Programming
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
35:1
35:3
10.4230/LIPIcs.DISC.2019.35
article
Brief Announcement: On Self-Adjusting Skip List Networks
Avin, Chen
1
https://orcid.org/0000-0002-6647-8002
Salem, Iosif
2
https://orcid.org/0000-0003-2810-2781
Schmid, Stefan
2
https://orcid.org/0000-0002-7798-1711
Communication Systems Engineering Department, Ben Gurion University of the Negev, Beersheva, Israel
Faculty of Computer Science, University of Vienna, Austria
This paper explores the design of dynamic network topologies which adjust to the workload they serve, in an online manner. Such self-adjusting networks (SANs) are enabled by emerging optical technologies, and can be found, e.g., in datacenters. SANs can be used to reduce routing costs by moving frequently communicating nodes topologically closer. This paper presents SANs which provide, for the first time, provable working set guarantees: the routing cost between node pairs is proportional to how recently these nodes communicated last time. Our SANs rely on skip lists (which serve as the topology) and provide additional interesting properties such as local routing.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.35/LIPIcs.DISC.2019.35.pdf
self-adjusting networks
skip lists
working set
online algorithms
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
36:1
36:3
10.4230/LIPIcs.DISC.2019.36
article
Brief Announcement: Streaming and Massively Parallel Algorithms for Edge Coloring
Behnezhad, Soheil
1
Derakhshan, Mahsa
1
Hajiaghayi, MohammadTaghi
1
Knittel, Marina
1
Saleh, Hamed
1
Department of Computer Science, University of Maryland, College Park, MD, USA
A valid edge-coloring of a graph is an assignment of "colors" to its edges such that no two incident edges receive the same color. The goal is to find a proper coloring that uses few colors. In this paper, we revisit this problem in two models of computation specific to massive graphs, the Massively Parallel Computations (MPC) model and the Graph Streaming model:
Massively Parallel Computation. We give a randomized MPC algorithm that w.h.p., returns a (1+o(1))Delta edge coloring in O(1) rounds using O~(n) space per machine and O(m) total space. The space per machine can also be further improved to n^{1-Omega(1)} if Delta = n^{Omega(1)}. This is, to our knowledge, the first constant round algorithm for a natural graph problem in the strongly sublinear regime of MPC. Our algorithm improves a previous result of Harvey et al. [SPAA 2018] which required n^{1+Omega(1)} space to achieve the same result.
Graph Streaming. Since the output of edge-coloring is as large as its input, we consider a standard variant of the streaming model where the output is also reported in a streaming fashion. The main challenge is that the algorithm cannot "remember" all the reported edge colors, yet has to output a proper edge coloring using few colors.
We give a one-pass O~(n)-space streaming algorithm that always returns a valid coloring and uses 5.44 Delta colors w.h.p., if the edges arrive in a random order. For adversarial order streams, we give another one-pass O~(n)-space algorithm that requires O(Delta^2) colors.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.36/LIPIcs.DISC.2019.36.pdf
Massively Parallel Computation
Streaming
Edge Coloring
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
37:1
37:3
10.4230/LIPIcs.DISC.2019.37
article
Brief Announcement: Memory Lower Bounds for Self-Stabilization
Blin, Lélia
1
https://orcid.org/0000-0003-0342-9243
Feuilloley, Laurent
2
https://orcid.org/0000-0002-3994-0898
Le Bouder, Gabriel
3
Sorbonne Université, CNRS, Université Evry-Val d'Essonne, LIP6 UMR 7606, Paris
Sorbonne Université, CNRS, LIP6 UMR 7606, Paris
Sorbonne Université, CNRS, ENS Paris-Saclay, LIP6 UMR 7606, Paris
In the context of self-stabilization, a silent algorithm guarantees that the communication registers (a.k.a register) of every node do not change once the algorithm has stabilized. At the end of the 90’s, Dolev et al. [Acta Inf. '99] showed that, for finding the centers of a graph, for electing a leader, or for constructing a spanning tree, every silent deterministic algorithm must use a memory of Omega(log n) bits per register in n-node networks. Similarly, Korman et al. [Dist. Comp. '07] proved, using the notion of proof-labeling-scheme, that, for constructing a minimum-weight spanning tree (MST), every silent algorithm must use a memory of Omega(log^2n) bits per register. It follows that requiring the algorithm to be silent has a cost in terms of memory space, while, in the context of self-stabilization, where every node constantly checks the states of its neighbors, the silence property can be of limited practical interest. In fact, it is known that relaxing this requirement results in algorithms with smaller space-complexity.
In this paper, we are aiming at measuring how much gain in terms of memory can be expected by using arbitrary deterministic self-stabilizing algorithms, not necessarily silent. To our knowledge, the only known lower bound on the memory requirement for deterministic general algorithms, also established at the end of the 90’s, is due to Beauquier et al. [PODC '99] who proved that registers of constant size are not sufficient for leader election algorithms. We improve this result by establishing the lower bound Omega(log log n) bits per register for deterministic self-stabilizing algorithms solving (Delta+1)-coloring, leader election or constructing a spanning tree in networks of maximum degree Delta.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.37/LIPIcs.DISC.2019.37.pdf
Space lower bound
memory tight bound
deterministic self-stabilization
leader election
anonymous
identifiers
state model
ring
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
38:1
38:3
10.4230/LIPIcs.DISC.2019.38
article
Brief Announcement: Wait-Free Universality of Consensus in the Infinite Arrival Model
Bonin, Grégoire
1
Mostéfaoui, Achour
1
Perrin, Matthieu
1
LS2N, Université de Nantes, France
In classical asynchronous distributed systems composed of a fixed number n of processes where some proportion may fail by crashing, many objects do not have a wait-free linearizable implementation (e.g. stacks, queues, etc.). It has been proved that consensus is universal in such systems, which means that this system augmented with consensus objects allows to implement any object that has a sequential specification. In this paper, we consider a more general system model called infinite arrival model where infinitely many processes may arrive and leave or crash during a run. We prove that consensus is still universal in this more general model. For that, we propose a universal construction based on a weak log that can be implementated using consensus objects.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.38/LIPIcs.DISC.2019.38.pdf
Concurrent object
Consensus
Infinite arrival model
Linearizability
Universal construction
Wait-freedom
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
39:1
39:3
10.4230/LIPIcs.DISC.2019.39
article
Brief Announcement: Asymmetric Distributed Trust
Cachin, Christian
1
Tackmann, Björn
2
University of Bern, Switzerland
DFINITY, Zurich, Switzerland
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.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.39/LIPIcs.DISC.2019.39.pdf
Quorums
consensus
distributed trust
blockchains
cryptocurrencies
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
40:1
40:3
10.4230/LIPIcs.DISC.2019.40
article
Brief Announcement: Implementing Byzantine Tolerant Distributed Ledger Objects
Cholvi, Vicent
1
Anta, Antonio Fernández
2
Georgiou, Chryssis
3
Nicolaou, Nicolas
4
Universitat Jaume I, Castellón de la Plana, Spain
IMDEA Networks Institute, Madrid, Spain
University of Cyprus, Nicosia, Cyprus
Algolysis Ltd, Lemesos, Cyprus
This work provides a proper formalization for Distributed Ledger Objects (as first defined in [Antonio Fernández Anta et al., 2018]), when processes may be Byzantine. The formal definitions are accompanied by algorithms to implement Byzantine Distributed Ledgers by utilizing a Byzantine Atomic Broadcast service.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.40/LIPIcs.DISC.2019.40.pdf
Distributed Ledger Object
Byzantine Faults
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
41:1
41:3
10.4230/LIPIcs.DISC.2019.41
article
Brief Announcement: Model Checking Rendezvous Algorithms for Robots with Lights in Euclidean Space
Défago, Xavier
1
https://orcid.org/0000-0002-2377-205X
Heriban, Adam
2
Tixeuil, Sébastien
2
https://orcid.org/0000-0002-0948-7172
Wada, Koichi
3
https://orcid.org/0000-0002-5351-1459
School of Computing, Tokyo Institute of Technology, Japan
Sorbonne Université, CNRS, LIP6, Paris, France
Faculty of Science and Engineering, Hosei University, Tokyo, Japan
This announces the first successful attempt at using model-checking techniques to verify the correctness of self-stabilizing distributed algorithms for robots evolving in a continuous environment. The study focuses on the problem of rendezvous of two robots with lights and presents a generic verification model for the SPIN model checker. It will be presented in full at an upcoming venue.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.41/LIPIcs.DISC.2019.41.pdf
Autonomous mobile robots
Rendezvous
Lights
Model Checking
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
42:1
42:3
10.4230/LIPIcs.DISC.2019.42
article
Brief Announcement: Massively Parallel Approximate Distance Sketches
Dinitz, Michael
1
Nazari, Yasamin
1
Johns Hopkins University, Baltimore, MD, United States
Data structures that allow efficient distance estimation have been extensively studied both in centralized models and classical distributed models. 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. 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 is 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.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.42/LIPIcs.DISC.2019.42.pdf
Distance Sketches
Massively Parallel Computation
Congested Clique
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
43:1
43:3
10.4230/LIPIcs.DISC.2019.43
article
Brief Announcement: Neighborhood Mutual Remainder and Its Self-Stabilizing Implementation of Look-Compute-Move Robots
Dolev, Shlomi
1
Kamei, Sayaka
2
Katayama, Yoshiaki
3
Ooshita, Fukuhito
4
Wada, Koichi
5
Department of Computer Science, Ben-Gurion University of the Negev, Beer-Sheva, Israel
Graduate School of Engineering, Hiroshima University, Japan
Graduate School of Engineering, Nagoya Institute of Technology, Japan
Graduate School of Science and Technology, Nara Institute of Science and Technology, Japan
Faculty of Science and Engineering, Hosei University, Japan
In this paper, we define a new concept neighborhood mutual remainder (NMR). An NMR distributed algorithms should satisfy global fairness, l-exclusion and repeated local rendezvous requirements. We give a simple self-stabilizing algorithm to demonstrate the design paradigm to achieve NMR, and also present applications of NMR to a Look-Compute-Move robot system.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.43/LIPIcs.DISC.2019.43.pdf
neighborhood mutual remainder
self-stabilization
LCM robot
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
44:1
44:3
10.4230/LIPIcs.DISC.2019.44
article
Brief Announcement: Revisiting Consensus Protocols through Wait-Free Parallelization
Gupta, Suyash
1
Hellings, Jelle
1
Sadoghi, Mohammad
1
Exploratory Systems Lab, Department of Computer Science, University of California, Davis, CA, USA
In this brief announcement, we propose a protocol-agnostic approach to improve the design of primary-backup consensus protocols. At the core of our approach is a novel wait-free design of running several instances of the underlying consensus protocol in parallel. To yield a high-performance parallelized design, we present coordination-free techniques to order operations across parallel instances, deal with instance failures, and assign clients to specific instances. Consequently, the design we present is able to reduce the load on individual instances and primaries, while also reducing the adverse effects of any malicious replicas. Our design is fine-tuned such that the instances coordinated by non-faulty replicas are wait-free: they can continuously make consensus decisions, independent of the behavior of any other instances.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.44/LIPIcs.DISC.2019.44.pdf
Consensus
primary-backup
high-performance
wait-free parallelization
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
45:1
45:3
10.4230/LIPIcs.DISC.2019.45
article
Brief Announcement: The Fault-Tolerant Cluster-Sending Problem
Hellings, Jelle
1
Sadoghi, Mohammad
1
Exploratory Systems Lab, Department of Computer Science, University of California, Davis, CA, USA
The development of fault-tolerant distributed systems that can tolerate Byzantine behavior has traditionally been focused on consensus protocols, which support fully-replicated designs. For the development of more sophisticated high-performance Byzantine distributed systems, more specialized fault-tolerant communication primitives are necessary, however.
In this brief announcement, we identify the cluster-sending problem - the problem of sending a message from one Byzantine cluster to another Byzantine cluster in a reliable manner - as such an essential communication primitive. We not only formalize this fundamental problem, but also establish lower bounds on the complexity of this problem under crash failures and Byzantine failures. Furthermore, we develop practical cluster-sending protocols that meet these lower bounds and, hence, have optimal complexity. As such, our work provides a strong foundation for the further exploration of novel designs that address challenges encountered in fault-tolerant distributed systems.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.45/LIPIcs.DISC.2019.45.pdf
Byzantine clusters
message sending
lower bound
optimal protocol
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
46:1
46:3
10.4230/LIPIcs.DISC.2019.46
article
Brief Announcement: On the Correctness of Transaction Processing with External Dependency
Javidi Kishi, Masoomeh
1
Hassan, Ahmed
2
Palmieri, Roberto
1
Lehigh University, Bethlehem, PA, USA
Alexandria University, Alexandria, Egypt
We briefly introduce a unified model to characterize correctness levels stronger (or equal to) serializability in the presence of application invariant. We propose to classify relations among committed transactions into data-related and application semantic-related. Our model delivers a condition that can be used to verify the safety of transactional executions in the presence of application invariant.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.46/LIPIcs.DISC.2019.46.pdf
Transactions
Dependency Graph
Concurrency
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
47:1
47:3
10.4230/LIPIcs.DISC.2019.47
article
Brief Announcement: Towards Byzantine Broadcast in Generalized Communication and Adversarial Models
Liu-Zhang, Chen-Da
1
https://orcid.org/0000-0002-0349-3838
Maram, Varun
1
Maurer, Ueli
1
Department of Computer Science, ETH Zurich, Switzerland
Byzantine broadcast is a primitive which allows a specific party to distribute a message consistently among n parties, even if up to t parties exhibit malicious behaviour. In the classical model with a complete network of bilateral authenticated channels, the seminal result of Pease et al. [Pease et al., 1980] shows that broadcast is achievable if and only if t < n/3. There are two generalizations suggested for the broadcast problem - w.r.t. the adversarial model and the communication model. Fitzi and Maurer [Fitzi and Maurer, 1998] consider a (non-threshold) general adversary that is characterized by the subsets of parties that could be corrupted, and show that broadcast can be realized from bilateral channels if and only if the union of no three possible corrupted sets equals the entire set of n parties. On the other hand, Considine et al. [Considine et al., 2005] extend the standard model of bilateral channels with the existence of b-minicast channels that allow to locally broadcast among any subset of b parties; the authors show that in this enhanced model of communication, secure broadcast tolerating up to t corrupted parties is possible if and only if t < (b-1)/(b+1) n. These generalizations are unified in the work by Raykov [Raykov P., 2015], where a tight condition on the possible corrupted sets such that broadcast is achievable from a complete set of b-minicasts is shown.
This paper investigates the achievability of broadcast in general networks, i.e., networks where only some subsets of minicast channels may be available, thereby addressing open problems posed in [Jaffe et al., 2012; Raykov P., 2015]. Our contributions include: 1) proposing a hierarchy over all possible general adversaries for a clean analysis of the broadcast problem in general networks, 2) showing the infeasibility of a prominent technique - used to achieve broadcast in general 3-minicast networks [Ravikant et al., 2004] - with regard to higher b-minicast networks, and 3) providing some necessary conditions on general networks for broadcast to be possible while tolerating general adversaries.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.47/LIPIcs.DISC.2019.47.pdf
broadcast
partial broadcast
minicast
general adversary
general network
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
48:1
48:3
10.4230/LIPIcs.DISC.2019.48
article
Brief Announcement: Integrating Temporal Information to Spatial Information in a Neural Circuit
Lynch, Nancy
1
Wang, Mien Brabeeba
1
Massachusetts Institute of Technology, Cambridge, MA, United States
In this paper, we consider networks of deterministic spiking neurons, firing synchronously at discrete times. We consider the problem of translating temporal information into spatial information in such networks, an important task that is carried out by actual brains. Specifically, we define two problems: "First Consecutive Spikes Counting" and "Total Spikes Counting", which model temporal-coding and rate-coding aspects of temporal-to-spatial translation respectively. Assuming an upper bound of T on the length of the temporal input signal, we design two networks that solve two problems, each using O(log T) neurons and terminating in time T+1. We also prove that these bounds are tight.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.48/LIPIcs.DISC.2019.48.pdf
Spiking Neural Network
Distributed Algorithm
Biological Networks
eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2019-10-08
146
49:1
49:3
10.4230/LIPIcs.DISC.2019.49
article
Brief Announcement: Faster Asynchronous MST and Low Diameter Tree Construction with Sublinear Communication
Mashreghi, Ali
1
King, Valerie
1
Department of Computer Science, University of Victoria, BC, Canada
Building a spanning tree, minimum spanning tree (MST), and BFS tree in a distributed network are fundamental problems which are still not fully understood in terms of time and communication cost. The first work to succeed in computing a spanning tree with communication sublinear in the number of edges in an asynchronous CONGEST network appeared in DISC 2018. That algorithm which constructs an MST is sequential in the worst case; its running time is proportional to the total number of messages sent. Our paper matches its message complexity but brings the running time down to linear in n. Our techniques can also be used to provide an asynchronous algorithm with sublinear communication to construct a tree in which the distance from a source to each node is within an additive term of sqrt{n} of its actual distance.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol146-disc2019/LIPIcs.DISC.2019.49/LIPIcs.DISC.2019.49.pdf
Distributed Computing
Minimum Spanning Tree
Broadcast Tree