Volume
LIPIcs, Volume 179
34th International Symposium on Distributed Computing (DISC 2020)
-
Part of:
Series:
Leibniz International Proceedings in Informatics (LIPIcs)
Conference: International Symposium on Distributed Computing (DISC)
Event
DISC 2020, October 12-16, 2020, Virtual ConferenceEditor
Publication Details
- published at: 2020-10-07
- Publisher: Schloss Dagstuhl – Leibniz-Zentrum für Informatik
- ISBN: 978-3-95977-168-9
- DBLP: db/conf/wdag/disc2020
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Complete Volume
LIPIcs, Volume 179, DISC 2020, Complete Volume
Abstract
LIPIcs, Volume 179, DISC 2020, Complete Volume
Cite as
34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 1-768, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@Proceedings{attiya:LIPIcs.DISC.2020,
title = {{LIPIcs, Volume 179, DISC 2020, Complete Volume}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {1--768},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020},
URN = {urn:nbn:de:0030-drops-130777},
doi = {10.4230/LIPIcs.DISC.2020},
annote = {Keywords: LIPIcs, Volume 179, DISC 2020, Complete Volume}
}
Document
Front Matter
Front Matter, Table of Contents, Preface, Conference Organization
Abstract
Front Matter, Table of Contents, Preface, Conference Organization
Cite as
34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 0:i-0:xviii, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{attiya:LIPIcs.DISC.2020.0,
author = {Attiya, Hagit},
title = {{Front Matter, Table of Contents, Preface, Conference Organization}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {0:i--0:xviii},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.0},
URN = {urn:nbn:de:0030-drops-130787},
doi = {10.4230/LIPIcs.DISC.2020.0},
annote = {Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
Improved Bounds for Distributed Load Balancing
Abstract
In the load balancing problem, the input is an n-vertex bipartite graph G = (C ∪ S, E) - where the two sides of the bipartite graph are referred to as the clients and the servers - and a positive weight for each client c ∈ C. The algorithm must assign each client c ∈ C to an adjacent server s ∈ S. The load of a server is then the weighted sum of all the clients assigned to it. The goal is to compute an assignment that minimizes some function of the server loads, typically either the maximum server load (i.e., the 𝓁_∞-norm) or the 𝓁_p-norm of the server loads. This problem has a variety of applications and has been widely studied under several different names, including: scheduling with restricted assignment, semi-matching, and distributed backup placement.
We study load balancing in the distributed setting. There are two existing results in the CONGEST model. Czygrinow et al. [DISC 2012] showed a 2-approximation for unweighted clients with round-complexity O(Δ⁵), where Δ is the maximum degree of the input graph. Halldórsson et al. [SPAA 2015] showed an O(log n / log log n)-approximation for unweighted clients and O(log²n/log log n)-approximation for weighted clients with round-complexity polylog(n).
In this paper, we show the first distributed algorithms to compute an O(1)-approximation to the load balancing problem in polylog(n) rounds:
- In the CONGEST model, we give an O(1)-approximation algorithm in polylog(n) rounds for unweighted clients. For weighted clients, the approximation ratio is O(log{n}).
- In the less constrained LOCAL model, we give an O(1)-approximation algorithm for weighted clients in polylog(n) rounds.
Our approach also has implications for the standard sequential setting in which we obtain the first O(1)-approximation for this problem that runs in near-linear time. A 2-approximation is already known, but it requires solving a linear program and is hence much slower. Finally, we note that all of our results simultaneously approximate all 𝓁_p-norms, including the 𝓁_∞-norm.
Cite as
Sepehr Assadi, Aaron Bernstein, and Zachary Langley. Improved Bounds for Distributed Load Balancing. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 1:1-1:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{assadi_et_al:LIPIcs.DISC.2020.1,
author = {Assadi, Sepehr and Bernstein, Aaron and Langley, Zachary},
title = {{Improved Bounds for Distributed Load Balancing}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {1:1--1:15},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.1},
URN = {urn:nbn:de:0030-drops-130798},
doi = {10.4230/LIPIcs.DISC.2020.1},
annote = {Keywords: Load Balancing, Distributed Algorithms, Matching, Semi-Matching}
}
Document
Intermediate Value Linearizability: A Quantitative Correctness Criterion
Abstract
Big data processing systems often employ batched updates and data sketches to estimate certain properties of large data. For example, a CountMin sketch approximates the frequencies at which elements occur in a data stream, and a batched counter counts events in batches. This paper focuses on correctness criteria for concurrent implementations of such objects. Specifically, we consider quantitative objects, whose return values are from a totally ordered domain, with a particular emphasis on (ε,δ)-bounded objects that estimate a numerical quantity with an error of at most ε with probability at least 1 - δ.
The de facto correctness criterion for concurrent objects is linearizability. Intuitively, under linearizability, when a read overlaps an update, it must return the object’s value either before the update or after it. Consider, for example, a single batched increment operation that counts three new events, bumping a batched counter’s value from 7 to 10. In a linearizable implementation of the counter, a read overlapping this update must return either 7 or 10. We observe, however, that in typical use cases, any intermediate value between 7 and 10 would also be acceptable. To capture this additional degree of freedom, we propose Intermediate Value Linearizability (IVL), a new correctness criterion that relaxes linearizability to allow returning intermediate values, for instance 8 in the example above. Roughly speaking, IVL allows reads to return any value that is bounded between two return values that are legal under linearizability. A key feature of IVL is that we can prove that concurrent IVL implementations of (ε,δ)-bounded objects are themselves (ε,δ)-bounded. To illustrate the power of this result, we give a straightforward and efficient concurrent implementation of an (ε, δ)-bounded CountMin sketch, which is IVL (albeit not linearizable).
Finally, we show that IVL allows for inherently cheaper implementations than linearizable ones. In particular, we show a lower bound of Ω(n) on the step complexity of the update operation of any wait-free linearizable batched counter from single-writer objects, and propose a wait-free IVL implementation of the same object with an O(1) step complexity for update.
Cite as
Arik Rinberg and Idit Keidar. Intermediate Value Linearizability: A Quantitative Correctness Criterion. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 2:1-2:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{rinberg_et_al:LIPIcs.DISC.2020.2,
author = {Rinberg, Arik and Keidar, Idit},
title = {{Intermediate Value Linearizability: A Quantitative Correctness Criterion}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {2:1--2:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.2},
URN = {urn:nbn:de:0030-drops-130801},
doi = {10.4230/LIPIcs.DISC.2020.2},
annote = {Keywords: concurrency, concurrent objects, linearizability}
}
Document
The Splay-List: A Distribution-Adaptive Concurrent Skip-List
Abstract
The design and implementation of efficient concurrent data structures has seen significant attention. However, most of this work has focused on concurrent data structures providing good worst-case guarantees. In real workloads, objects are often accessed at different rates, since access distributions may be non-uniform. Efficient distribution-adaptive data structures are known in the sequential case, e.g. the splay-trees; however, they often are hard to translate efficiently in the concurrent case.
In this paper, we investigate distribution-adaptive concurrent data structures, and propose a new design called the splay-list. At a high level, the splay-list is similar to a standard skip-list, with the key distinction that the height of each element adapts dynamically to its access rate: popular elements "move up," whereas rarely-accessed elements decrease in height. We show that the splay-list provides order-optimal amortized complexity bounds for a subset of operations, while being amenable to efficient concurrent implementation. Experimental results show that the splay-list can leverage distribution-adaptivity to improve on the performance of classic concurrent designs, and can outperform the only previously-known distribution-adaptive design in certain settings.
Cite as
Vitaly Aksenov, Dan Alistarh, Alexandra Drozdova, and Amirkeivan Mohtashami. The Splay-List: A Distribution-Adaptive Concurrent Skip-List. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 3:1-3:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{aksenov_et_al:LIPIcs.DISC.2020.3,
author = {Aksenov, Vitaly and Alistarh, Dan and Drozdova, Alexandra and Mohtashami, Amirkeivan},
title = {{The Splay-List: A Distribution-Adaptive Concurrent Skip-List}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {3:1--3:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.3},
URN = {urn:nbn:de:0030-drops-130818},
doi = {10.4230/LIPIcs.DISC.2020.3},
annote = {Keywords: Data structures, self-adjusting, concurrency}
}
Document
Efficient Multi-Word Compare and Swap
Abstract
Atomic lock-free multi-word compare-and-swap (MCAS) is a powerful tool for designing concurrent algorithms. Yet, its widespread usage has been limited because lock-free implementations of MCAS make heavy use of expensive compare-and-swap (CAS) instructions. Existing MCAS implementations indeed use at least 2k+1 CASes per k-CAS. This leads to the natural desire to minimize the number of CASes required to implement MCAS.
We first prove in this paper that it is impossible to "pack" the information required to perform a k-word CAS (k-CAS) in less than k locations to be CASed. Then we present the first algorithm that requires k+1 CASes per call to k-CAS in the common uncontended case. We implement our algorithm and show that it outperforms a state-of-the-art baseline in a variety of benchmarks in most considered workloads. We also present a durably linearizable (persistent memory friendly) version of our MCAS algorithm using only 2 persistence fences per call, while still only requiring k+1 CASes per k-CAS.
Cite as
Rachid Guerraoui, Alex Kogan, Virendra J. Marathe, and Igor Zablotchi. Efficient Multi-Word Compare and Swap. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 4:1-4:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{guerraoui_et_al:LIPIcs.DISC.2020.4,
author = {Guerraoui, Rachid and Kogan, Alex and Marathe, Virendra J. and Zablotchi, Igor},
title = {{Efficient Multi-Word Compare and Swap}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {4:1--4:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.4},
URN = {urn:nbn:de:0030-drops-130827},
doi = {10.4230/LIPIcs.DISC.2020.4},
annote = {Keywords: lock-free, multi-word compare-and-swap, persistent memory}
}
Document
LL/SC and Atomic Copy: Constant Time, Space Efficient Implementations Using Only Pointer-Width CAS
Abstract
When designing concurrent algorithms, Load-Link/Store-Conditional (LL/SC) is a very useful primitive since it avoids ABA problems. The full semantics of LL/SC are not supported in hardware by any modern architecture, so there has been a significant amount of work on simulations of LL/SC using CAS. However, all previous algorithms that are constant time either use unbounded sequence numbers (and thus base objects of unbounded size), or require Ω(MP) space to implement M LL/SC objects for P processes.
We present the first constant time implementation of LL/SC from bounded-sized CAS objects using only constant space overhead per LL/SC variable. In particular, our implementation uses Θ(M+kP²) space, where k is the number of outstanding LL operations per process, and only requires pointer-width CAS operations. In most algorithms that use LL/SC, k is a small constant which reduces our additive space overhead to Θ(P²). Our algorithm can also be extended to implement L word LL/SC objects in Θ(L) time for LL and SC, O(1) time for VL, and Θ((M+kP²)L) space.
To achieve these bounds, our main technical contribution is implementing a new primitive called Single-Writer Copy which takes a pointer to a word sized memory location and atomically copies its contents into another object. The restriction is that only one process is allowed to write/copy into the destination object at a time. The ability to read from one memory location and write to another atomically, and in constant-time, is very powerful and we believe this primitive will be useful in designing other algorithms.
Cite as
Guy E. Blelloch and Yuanhao Wei. LL/SC and Atomic Copy: Constant Time, Space Efficient Implementations Using Only Pointer-Width CAS. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 5:1-5:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{blelloch_et_al:LIPIcs.DISC.2020.5,
author = {Blelloch, Guy E. and Wei, Yuanhao},
title = {{LL/SC and Atomic Copy: Constant Time, Space Efficient Implementations Using Only Pointer-Width CAS}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {5:1--5:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.5},
URN = {urn:nbn:de:0030-drops-130831},
doi = {10.4230/LIPIcs.DISC.2020.5},
annote = {Keywords: LL/SC, Atomic Copy, CAS, Constant Time}
}
Document
Message Complexity of Population Protocols
Abstract
The standard population protocol model assumes that when two agents interact, each observes the entire state of the other. We initiate the study of message complexity for population protocols, where an agent’s state is divided into an externally-visible message and externally-hidden local state.
We consider the case of O(1) message complexity. When time is unrestricted, we obtain an exact characterization of the stably computable predicates based on the number of internal states s(n): If s(n) = o(n) then the protocol computes semilinear predicates (unlike the original model, which can compute non-semilinear predicates with s(n) = O(log n)), and otherwise it computes a predicate decidable by a nondeterministic O(n log s(n))-space-bounded Turing machine. We then introduce novel O(polylog(n)) expected time protocols for junta/leader election and general purpose broadcast correct with high probability, and approximate and exact population size counting correct with probability 1. Finally, we show that the main constraint on the power of bounded-message-size protocols is the size of the internal states: with unbounded internal states, any computable function can be computed with probability 1 in the limit by a protocol that uses only 1-bit messages.
Cite as
Talley Amir, James Aspnes, David Doty, Mahsa Eftekhari, and Eric Severson. Message Complexity of Population Protocols. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 6:1-6:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{amir_et_al:LIPIcs.DISC.2020.6,
author = {Amir, Talley and Aspnes, James and Doty, David and Eftekhari, Mahsa and Severson, Eric},
title = {{Message Complexity of Population Protocols}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {6:1--6:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.6},
URN = {urn:nbn:de:0030-drops-130848},
doi = {10.4230/LIPIcs.DISC.2020.6},
annote = {Keywords: population protocol, message complexity, space-optimal}
}
Document
Distributed Computation with Continual Population Growth
Abstract
Computing with synthetically engineered bacteria is a vibrant and active field with numerous applications in bio-production, bio-sensing, and medicine. Motivated by the lack of robustness and by resource limitation inside single cells, distributed approaches with communication among bacteria have recently gained in interest. In this paper, we focus on the problem of population growth happening concurrently, and possibly interfering, with the desired bio-computation. Specifically, we present a fast protocol in systems with continuous population growth for the majority consensus problem and prove that it correctly identifies the initial majority among two inputs with high probability if the initial difference is Ω(√{nlog n}) where n is the total initial population. We also present a fast protocol that correctly computes the NAND of two inputs with high probability. We demonstrate that combining the NAND gate protocol with the continuous-growth majority consensus protocol, using the latter as an amplifier, it is possible to implement circuits computing arbitrary Boolean functions.
Cite as
Da-Jung Cho, Matthias Függer, Corbin Hopper, Manish Kushwaha, Thomas Nowak, and Quentin Soubeyran. Distributed Computation with Continual Population Growth. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 7:1-7:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{cho_et_al:LIPIcs.DISC.2020.7,
author = {Cho, Da-Jung and F\"{u}gger, Matthias and Hopper, Corbin and Kushwaha, Manish and Nowak, Thomas and Soubeyran, Quentin},
title = {{Distributed Computation with Continual Population Growth}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {7:1--7:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.7},
URN = {urn:nbn:de:0030-drops-130856},
doi = {10.4230/LIPIcs.DISC.2020.7},
annote = {Keywords: microbiological circuits, majority consensus, birth-death processes}
}
Document
Who Started This Rumor? Quantifying the Natural Differential Privacy of Gossip Protocols
Abstract
Gossip protocols (also called rumor spreading or epidemic protocols) are widely used to disseminate information in massive peer-to-peer networks. These protocols are often claimed to guarantee privacy because of the uncertainty they introduce on the node that started the dissemination. But is that claim really true? Can the source of a gossip safely hide in the crowd? This paper examines, for the first time, gossip protocols through a rigorous mathematical framework based on differential privacy to determine the extent to which the source of a gossip can be traceable. Considering the case of a complete graph in which a subset of the nodes are curious, we study a family of gossip protocols parameterized by a "muting" parameter s: nodes stop emitting after each communication with a fixed probability 1-s. We first prove that the standard push protocol, corresponding to the case s = 1, does not satisfy differential privacy for large graphs. In contrast, the protocol with s = 0 (nodes forward only once) achieves optimal privacy guarantees but at the cost of a drastic increase in the spreading time compared to standard push, revealing an interesting tension between privacy and spreading time. Yet, surprisingly, we show that some choices of the muting parameter s lead to protocols that achieve an optimal order of magnitude in both privacy and speed. Privacy guarantees are obtained by showing that only a small fraction of the possible observations by curious nodes have different probabilities when two different nodes start the gossip, since the source node rapidly stops emitting when s is small. The speed is established by analyzing the mean dynamics of the protocol, and leveraging concentration inequalities to bound the deviations from this mean behavior. We also confirm empirically that, with appropriate choices of s, we indeed obtain protocols that are very robust against concrete source location attacks (such as maximum a posteriori estimates) while spreading the information almost as fast as the standard (and non-private) push protocol.
Cite as
Aurélien Bellet, Rachid Guerraoui, and Hadrien Hendrikx. Who Started This Rumor? Quantifying the Natural Differential Privacy of Gossip Protocols. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 8:1-8:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{bellet_et_al:LIPIcs.DISC.2020.8,
author = {Bellet, Aur\'{e}lien and Guerraoui, Rachid and Hendrikx, Hadrien},
title = {{Who Started This Rumor? Quantifying the Natural Differential Privacy of Gossip Protocols}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {8:1--8:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.8},
URN = {urn:nbn:de:0030-drops-130868},
doi = {10.4230/LIPIcs.DISC.2020.8},
annote = {Keywords: Gossip Protocol, Rumor Spreading, Differential Privacy}
}
Document
Spread of Information and Diseases via Random Walks in Sparse Graphs
Abstract
We consider a natural network diffusion process, modeling the spread of information or infectious diseases. Multiple mobile agents perform independent simple random walks on an n-vertex connected graph G. The number of agents is linear in n and the walks start from the stationary distribution. Initially, a single vertex has a piece of information (or a virus). An agent becomes informed (or infected) the first time it visits some vertex with the information (or virus); thereafter, the agent informs (infects) all vertices it visits. Giakkoupis et al. [George Giakkoupis et al., 2019] have shown that the spreading time, i.e., the time before all vertices are informed, is asymptotically and w.h.p. the same as in the well-studied randomized rumor spreading process, on any d-regular graph with d = Ω(log n). The case of sub-logarithmic degree was left open, and is the main focus of this paper.
First, we observe that the equivalence shown in [George Giakkoupis et al., 2019] does not hold for small d: We give an example of a 3-regular graph with logarithmic diameter for which the expected spreading time is Ω(log² n/log log n), whereas randomized rumor spreading is completed in time Θ(log n), w.h.p. Next, we show a general upper bound of Õ(d ⋅ diam(G) + log³ n /d), w.h.p., for the spreading time on any d-regular graph. We also provide a version of the bound based on the average degree, for non-regular graphs. Next, we give tight analyses for specific graph families. We show that the spreading time is O(log n), w.h.p., for constant-degree regular expanders. For the binary tree, we show an upper bound of O(log n⋅ log log n), w.h.p., and prove that this is tight, by giving a matching lower bound for the cover time of the tree by n random walks. Finally, we show a bound of O(diam(G)), w.h.p., for k-dimensional grids (k ≥ 1 is constant), by adapting a technique by Kesten and Sidoravicius [Kesten and Sidoravicius, 2003; Kesten and Sidoravicius, 2005].
Cite as
George Giakkoupis, Hayk Saribekyan, and Thomas Sauerwald. Spread of Information and Diseases via Random Walks in Sparse Graphs. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 9:1-9:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{giakkoupis_et_al:LIPIcs.DISC.2020.9,
author = {Giakkoupis, George and Saribekyan, Hayk and Sauerwald, Thomas},
title = {{Spread of Information and Diseases via Random Walks in Sparse Graphs}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {9:1--9:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.9},
URN = {urn:nbn:de:0030-drops-130873},
doi = {10.4230/LIPIcs.DISC.2020.9},
annote = {Keywords: parallel random walks, information dissemination, infectious diseases}
}
Document
Spiking Neural Networks Through the Lens of Streaming Algorithms
Abstract
We initiate the study of biologically-inspired spiking neural networks from the perspective of streaming algorithms. Like computers, human brains face memory limitations, which pose a significant obstacle when processing large scale and dynamically changing data. In computer science, these challenges are captured by the well-known streaming model, which can be traced back to Munro and Paterson `78 and has had significant impact in theory and beyond. In the classical streaming setting, one must compute a function f of a stream of updates 𝒮 = {u₁,…,u_m}, given restricted single-pass access to the stream. The primary complexity measure is the space used by the algorithm.
In contrast to the large body of work on streaming algorithms, relatively little is known about the computational aspects of data processing in spiking neural networks. In this work, we seek to connect these two models, leveraging techniques developed for streaming algorithms to better understand neural computation. Our primary goal is to design networks for various computational tasks using as few auxiliary (non-input or output) neurons as possible. The number of auxiliary neurons can be thought of as the "space" required by the network.
Previous algorithmic work in spiking neural networks has many similarities with streaming algorithms. However, the connection between these two space-limited models has not been formally addressed. We take the first steps towards understanding this connection. On the upper bound side, we design neural algorithms based on known streaming algorithms for fundamental tasks, including distinct elements, approximate median, and heavy hitters. The number of neurons in our solutions almost match the space bounds of the corresponding streaming algorithms. As a general algorithmic primitive, we show how to implement the important streaming technique of linear sketching efficiently in spiking neural networks. On the lower bound side, we give a generic reduction, showing that any space-efficient spiking neural network can be simulated by a space-efficient streaming algorithm. This reduction lets us translate streaming-space lower bounds into nearly matching neural-space lower bounds, establishing a close connection between the two models.
Cite as
Yael Hitron, Cameron Musco, and Merav Parter. Spiking Neural Networks Through the Lens of Streaming Algorithms. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 10:1-10:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{hitron_et_al:LIPIcs.DISC.2020.10,
author = {Hitron, Yael and Musco, Cameron and Parter, Merav},
title = {{Spiking Neural Networks Through the Lens of Streaming Algorithms}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {10:1--10:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.10},
URN = {urn:nbn:de:0030-drops-130882},
doi = {10.4230/LIPIcs.DISC.2020.10},
annote = {Keywords: Biological distributed algorithms, Spiking neural networks, Streaming algorithms}
}
Document
Communication Efficient Self-Stabilizing Leader Election
Abstract
This paper presents a randomized self-stabilizing algorithm that elects a leader r in a general n-node undirected graph and constructs a spanning tree T rooted at r. The algorithm works under the synchronous message passing network model, assuming that the nodes know a linear upper bound on n and that each edge has a unique ID known to both its endpoints (or, alternatively, assuming the KT₁ model). The highlight of this algorithm is its superior communication efficiency: It is guaranteed to send a total of Õ (n) messages, each of constant size, till stabilization, while stabilizing in Õ (n) rounds, in expectation and with high probability. After stabilization, the algorithm sends at most one constant size message per round while communicating only over the (n - 1) edges of T. In all these aspects, the communication overhead of the new algorithm is far smaller than that of the existing (mostly deterministic) self-stabilizing leader election algorithms.
The algorithm is relatively simple and relies mostly on known modules that are common in the fault free leader election literature; these modules are enhanced in various subtle ways in order to assemble them into a communication efficient self-stabilizing algorithm.
Cite as
Xavier Défago, Yuval Emek, Shay Kutten, Toshimitsu Masuzawa, and Yasumasa Tamura. Communication Efficient Self-Stabilizing Leader Election. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 11:1-11:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{defago_et_al:LIPIcs.DISC.2020.11,
author = {D\'{e}fago, Xavier and Emek, Yuval and Kutten, Shay and Masuzawa, Toshimitsu and Tamura, Yasumasa},
title = {{Communication Efficient Self-Stabilizing Leader Election}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {11:1--11:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.11},
URN = {urn:nbn:de:0030-drops-130892},
doi = {10.4230/LIPIcs.DISC.2020.11},
annote = {Keywords: self-stabilization, leader election, communication overhead}
}
Document
Gathering on a Circle with Limited Visibility by Anonymous Oblivious Robots
Abstract
A swarm of anonymous oblivious mobile robots, operating in deterministic Look-Compute-Move cycles, is confined within a circular track. All robots agree on the clockwise direction (chirality), they are activated by an adversarial semi-synchronous scheduler (SSYNCH), and an active robot always reaches the destination point it computes (rigidity). Robots have limited visibility: each robot can see only the points on the circle that have an angular distance strictly smaller than a constant ϑ from the robot’s current location, where 0 < ϑ ≤ π (angles are expressed in radians).
We study the Gathering problem for such a swarm of robots: that is, all robots are initially in distinct locations on the circle, and their task is to reach the same point on the circle in a finite number of turns, regardless of the way they are activated by the scheduler. Note that, due to the anonymity of the robots, this task is impossible if the initial configuration is rotationally symmetric; hence, we have to make the assumption that the initial configuration be rotationally asymmetric.
We prove that, if ϑ = π (i.e., each robot can see the entire circle except its antipodal point), there is a distributed algorithm that solves the Gathering problem for swarms of any size. By contrast, we also prove that, if ϑ ≤ π/2, no distributed algorithm solves the Gathering problem, regardless of the size of the swarm, even under the assumption that the initial configuration is rotationally asymmetric and the visibility graph of the robots is connected.
The latter impossibility result relies on a probabilistic technique based on random perturbations, which is novel in the context of anonymous mobile robots. Such a technique is of independent interest, and immediately applies to other Pattern-Formation problems.
Cite as
Giuseppe A. Di Luna, Ryuhei Uehara, Giovanni Viglietta, and Yukiko Yamauchi. Gathering on a Circle with Limited Visibility by Anonymous Oblivious Robots. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 12:1-12:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{diluna_et_al:LIPIcs.DISC.2020.12,
author = {Di Luna, Giuseppe A. and Uehara, Ryuhei and Viglietta, Giovanni and Yamauchi, Yukiko},
title = {{Gathering on a Circle with Limited Visibility by Anonymous Oblivious Robots}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {12:1--12:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.12},
URN = {urn:nbn:de:0030-drops-130907},
doi = {10.4230/LIPIcs.DISC.2020.12},
annote = {Keywords: Mobile robots, Gathering, limited visibility, circle}
}
Document
Tight Bounds for Deterministic High-Dimensional Grid Exploration
Abstract
We study the problem of exploring an oriented grid with autonomous agents governed by finite automata. In the case of a 2-dimensional grid, the question how many agents are required to explore the grid, or equivalently, find a hidden treasure in the grid, is fully understood in both the synchronous and the semi-synchronous setting. For higher dimensions, Dobrev, Narayanan, Opatrny, and Pankratov [ICALP'19] showed very recently that, surprisingly, a (small) constant number of agents suffices to find the treasure, independent of the number of dimensions, thereby disproving a conjecture by Cohen, Emek, Louidor, and Uitto [SODA'17]. Dobrev et al. left as an open question whether their bounds on the number of agents can be improved. We answer this question in the affirmative for deterministic finite automata: we show that 3 synchronous and 4 semi-synchronous agents suffice to explore an n-dimensional grid for any constant n. The bounds are optimal and notably, the matching lower bounds already hold in the 2-dimensional case.
Our techniques can also be used to make progress on other open questions asked by Dobrev et al.: we prove that 4 synchronous and 5 semi-synchronous agents suffice for polynomial-time exploration, and we show that, under a natural assumption, 3 synchronous and 4 semi-synchronous agents suffice to explore unoriented grids of arbitrary dimension (which, again, is tight).
Cite as
Sebastian Brandt, Julian Portmann, and Jara Uitto. Tight Bounds for Deterministic High-Dimensional Grid Exploration. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 13:1-13:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{brandt_et_al:LIPIcs.DISC.2020.13,
author = {Brandt, Sebastian and Portmann, Julian and Uitto, Jara},
title = {{Tight Bounds for Deterministic High-Dimensional Grid Exploration}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {13:1--13:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.13},
URN = {urn:nbn:de:0030-drops-130911},
doi = {10.4230/LIPIcs.DISC.2020.13},
annote = {Keywords: Mobile agents, finite automata, grid search}
}
Document
Distributed Dispatching in the Parallel Server Model
Abstract
With the rapid increase in the size and volume of cloud services and data centers, architectures with multiple job dispatchers are quickly becoming the norm. Load balancing is a key element of such systems. Nevertheless, current solutions to load balancing in such systems admit a paradoxical behavior in which more accurate information regarding server queue lengths degrades performance due to herding and detrimental incast effects. Indeed, both in theory and in practice, there is a common doubt regarding the value of information in the context of multi-dispatcher load balancing. As a result, both researchers and system designers resort to more straightforward solutions, such as the power-of-two-choices to avoid worst-case scenarios, potentially sacrificing overall resource utilization and system performance. A principal focus of our investigation concerns the value of information about queue lengths in the multi-dispatcher setting. We argue that, at its core, load balancing with multiple dispatchers is a distributed computing task. In that light, we propose a new job dispatching approach, called Tidal Water Filling, which addresses the distributed nature of the system. Specifically, by incorporating the existence of other dispatchers into the decision-making process, our protocols outperform previous solutions in many scenarios. In particular, when the dispatchers have complete and accurate information regarding the server queue lengths, our policies significantly outperform all existing solutions.
Cite as
Guy Goren, Shay Vargaftik, and Yoram Moses. Distributed Dispatching in the Parallel Server Model. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 14:1-14:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{goren_et_al:LIPIcs.DISC.2020.14,
author = {Goren, Guy and Vargaftik, Shay and Moses, Yoram},
title = {{Distributed Dispatching in the Parallel Server Model}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {14:1--14:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.14},
URN = {urn:nbn:de:0030-drops-130929},
doi = {10.4230/LIPIcs.DISC.2020.14},
annote = {Keywords: Distributed load balancing, Join the Shortest Queue, Tidal Water Filling, Parallel Server Model}
}
Document
Distributed Dense Subgraph Detection and Low Outdegree Orientation
Abstract
The densest subgraph problem, introduced in the 80s by Picard and Queyranne [Networks 1982] as well as Goldberg [Tech. Report 1984], is a classic problem in combinatorial optimization with a wide range of applications. The lowest outdegree orientation problem is known to be its dual problem. We study both the problem of finding dense subgraphs and the problem of computing a low outdegree orientation in the distributed settings.
Suppose G = (V,E) is the underlying network as well as the input graph. Let D denote the density of the maximum density subgraph of G. Our main results are as follows.
- Given a value D̃ ≤ D and 0 < ε < 1, we show that a subgraph with density at least (1-ε)D̃ can be identified deterministically in O((log n) / ε) rounds in the LOCAL model. We also present a lower bound showing that our result for the LOCAL model is tight up to an O(log n) factor.
In the CONGEST~ model, we show that such a subgraph can be identified in O((log³ n) / ε³) rounds with high probability. Our techniques also lead to an O(diameter + (log⁴ n)/ε⁴)-round algorithm that yields a 1-ε approximation to the densest subgraph. This improves upon the previous O(diameter /ε ⋅ log n)-round algorithm by Das Sarma et al. [DISC 2012] that only yields a 1/2-ε approximation.
- Given an integer D̃ ≥ D and Ω(1/D̃) < ε < 1/4, we give a deterministic, Õ((log² n) /ε²)-round algorithm in the CONGEST~ model that computes an orientation where the outdegree of every vertex is upper bounded by (1+ε)D̃. Previously, the best deterministic algorithm and randomized algorithm by Harris [FOCS 2019] run in Õ((log⁶ n)/ ε⁴) rounds and Õ((log³ n) /ε³) rounds respectively and only work in the LOCAL model.
Cite as
Hsin-Hao Su and Hoa T. Vu. Distributed Dense Subgraph Detection and Low Outdegree Orientation. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 15:1-15:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{su_et_al:LIPIcs.DISC.2020.15,
author = {Su, Hsin-Hao and Vu, Hoa T.},
title = {{Distributed Dense Subgraph Detection and Low Outdegree Orientation}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {15:1--15:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.15},
URN = {urn:nbn:de:0030-drops-130938},
doi = {10.4230/LIPIcs.DISC.2020.15},
annote = {Keywords: Distributed Algorithms, Network Algorithms}
}
Document
Local Conflict Coloring Revisited: Linial for Lists
Abstract
Linial’s famous color reduction algorithm reduces a given m-coloring of a graph with maximum degree Δ to a O(Δ²log m)-coloring, in a single round in the LOCAL model. We show a similar result when nodes are restricted to choose their color from a list of allowed colors: given an m-coloring in a directed graph of maximum outdegree β, if every node has a list of size Ω(β² (log β+log log m + log log |𝒞|)) from a color space 𝒞 then they can select a color in two rounds in the LOCAL model. Moreover, the communication of a node essentially consists of sending its list to the neighbors. This is obtained as part of a framework that also contains Linial’s color reduction (with an alternative proof) as a special case. Our result also leads to a defective list coloring algorithm. As a corollary, we improve the state-of-the-art truly local (deg+1)-list coloring algorithm from Barenboim et al. [PODC'18] by slightly reducing the runtime to O(√{ΔlogΔ})+log^* n and significantly reducing the message size (from huge to roughly Δ). Our techniques are inspired by the local conflict coloring framework of Fraigniaud et al. [FOCS'16].
Cite as
Yannic Maus and Tigran Tonoyan. Local Conflict Coloring Revisited: Linial for Lists. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 16:1-16:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{maus_et_al:LIPIcs.DISC.2020.16,
author = {Maus, Yannic and Tonoyan, Tigran},
title = {{Local Conflict Coloring Revisited: Linial for Lists}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {16:1--16:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.16},
URN = {urn:nbn:de:0030-drops-130944},
doi = {10.4230/LIPIcs.DISC.2020.16},
annote = {Keywords: distributed graph coloring, list coloring, low intersecting set families}
}
Document
Classification of Distributed Binary Labeling Problems
Abstract
We present a complete classification of the deterministic distributed time complexity for a family of graph problems: binary labeling problems in trees. These are locally checkable problems that can be encoded with an alphabet of size two in the edge labeling formalism. Examples of binary labeling problems include sinkless orientation, sinkless and sourceless orientation, 2-vertex coloring, perfect matching, and the task of coloring edges red and blue such that all nodes are incident to at least one red and at least one blue edge. More generally, we can encode e.g. any cardinality constraints on indegrees and outdegrees.
We study the deterministic time complexity of solving a given binary labeling problem in trees, in the usual LOCAL model of distributed computing. We show that the complexity of any such problem is in one of the following classes: O(1), Θ(log n), Θ(n), or unsolvable. In particular, a problem that can be represented in the binary labeling formalism cannot have time complexity Θ(log^* n), and hence we know that e.g. any encoding of maximal matchings has to use at least three labels (which is tight).
Furthermore, given the description of any binary labeling problem, we can easily determine in which of the four classes it is and what is an asymptotically optimal algorithm for solving it. Hence the distributed time complexity of binary labeling problems is decidable, not only in principle, but also in practice: there is a simple and efficient algorithm that takes the description of a binary labeling problem and outputs its distributed time complexity.
Cite as
Alkida Balliu, Sebastian Brandt, Yuval Efron, Juho Hirvonen, Yannic Maus, Dennis Olivetti, and Jukka Suomela. Classification of Distributed Binary Labeling Problems. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 17:1-17:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{balliu_et_al:LIPIcs.DISC.2020.17,
author = {Balliu, Alkida and Brandt, Sebastian and Efron, Yuval and Hirvonen, Juho and Maus, Yannic and Olivetti, Dennis and Suomela, Jukka},
title = {{Classification of Distributed Binary Labeling Problems}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {17:1--17:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.17},
URN = {urn:nbn:de:0030-drops-130957},
doi = {10.4230/LIPIcs.DISC.2020.17},
annote = {Keywords: LOCAL model, graph problems, locally checkable labeling problems, distributed computational complexity}
}
Document
The Complexity Landscape of Distributed Locally Checkable Problems on Trees
Abstract
Recent research revealed the existence of gaps in the complexity landscape of locally checkable labeling (LCL) problems in the LOCAL model of distributed computing. For example, the deterministic round complexity of any LCL problem on bounded-degree graphs is either O(log^∗ n) or Ω(log n) [Chang, Kopelowitz, and Pettie, FOCS 2016]. The complexity landscape of LCL problems is now quite well-understood, but a few questions remain open.
For bounded-degree trees, there is an LCL problem with round complexity Θ(n^{1/k}) for each positive integer k [Chang and Pettie, FOCS 2017]. It is conjectured that no LCL problem has round complexity o(n^{1/(k-1)}) and ω(n^{1/k}) on bounded-degree trees. As of now, only the case of k = 2 has been proved [Balliu et al., DISC 2018].
In this paper, we show that for LCL problems on bounded-degree trees, there is indeed a gap between Θ(n^{1/(k-1)}) and Θ(n^{1/k}) for each k ≥ 2. Our proof is constructive in the sense that it offers a sequential algorithm that decides which side of the gap a given LCL problem belongs to. We also show that it is EXPTIME-hard to distinguish between Θ(1)-round and Θ(n)-round LCL problems on bounded-degree trees. This improves upon a previous PSPACE-hardness result [Balliu et al., PODC 2019].
Cite as
Yi-Jun Chang. The Complexity Landscape of Distributed Locally Checkable Problems on Trees. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 18:1-18:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{chang:LIPIcs.DISC.2020.18,
author = {Chang, Yi-Jun},
title = {{The Complexity Landscape of Distributed Locally Checkable Problems on Trees}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {18:1--18:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.18},
URN = {urn:nbn:de:0030-drops-130964},
doi = {10.4230/LIPIcs.DISC.2020.18},
annote = {Keywords: Distributed algorithms, LOCAL model, locally checkable labeling}
}
Document
Improved Hardness of Approximation of Diameter in the CONGEST Model
Abstract
We study the problem of approximating the diameter D of an unweighted and undirected n-node graph in the congest model. Through a connection to extremal combinatorics, we show that a (6/11 + ε)-approximation requires Ω(n^{1/6}/log n) rounds, a (4/7 + ε)-approximation requires Ω(n^{1/4}/log n) rounds, and a (3/5 + ε)-approximation requires Ω(n^{1/3}/log n) rounds. These lower bounds are robust in the sense that they hold even against algorithms that are allowed to return an additional small additive error. Prior to our work, only lower bounds for (2/3 + ε)-approximation were known [Frischknecht et al. SODA 2012, Abboud et al. DISC 2016].
Furthermore, we prove that distinguishing graphs of diameter 3 from graphs of diameter 5 requires Ω(n/log n) rounds. This stands in sharp contrast to previous work: while there is an algorithm that returns an estimate ⌊ 2/3D ⌋ ≤ D̃ ≤ D in Õ(√n+D) rounds [Holzer et al. DISC 2014], our lower bound implies that any algorithm for returning an estimate 2/3D ≤ D̃ ≤ D requires ̃Ω(n) rounds.
Cite as
Ofer Grossman, Seri Khoury, and Ami Paz. Improved Hardness of Approximation of Diameter in the CONGEST Model. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 19:1-19:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{grossman_et_al:LIPIcs.DISC.2020.19,
author = {Grossman, Ofer and Khoury, Seri and Paz, Ami},
title = {{Improved Hardness of Approximation of Diameter in the CONGEST Model}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {19:1--19:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.19},
URN = {urn:nbn:de:0030-drops-130972},
doi = {10.4230/LIPIcs.DISC.2020.19},
annote = {Keywords: Distributed graph algorithms, Approximation algorithms, Lower bounds}
}
Document
Twenty-Two New Approximate Proof Labeling Schemes
Abstract
Introduced by Korman, Kutten, and Peleg (Distributed Computing 2005), a proof labeling scheme (PLS) is a system dedicated to verifying that a given configuration graph satisfies a certain property. It is composed of a centralized prover, whose role is to generate a proof for yes-instances in the form of an assignment of labels to the nodes, and a distributed verifier, whose role is to verify the validity of the proof by local means and accept it if and only if the property is satisfied. To overcome lower bounds on the label size of PLSs for certain graph properties, Censor-Hillel, Paz, and Perry (SIROCCO 2017) introduced the notion of an approximate proof labeling scheme (APLS) that allows the verifier to accept also some no-instances as long as they are not "too far" from satisfying the property.
The goal of the current paper is to advance our understanding of the power and limitations of APLSs. To this end, we formulate the notion of APLSs in terms of distributed graph optimization problems (OptDGPs) and develop two generic methods for the design of APLSs. These methods are then applied to various classic OptDGPs, obtaining twenty-two new APLSs. An appealing characteristic of our APLSs is that they are all sequentially efficient in the sense that both the prover and the verifier are required to run in (sequential) polynomial time. On the negative side, we establish "combinatorial" lower bounds on the label size for some of the aforementioned OptDGPs that demonstrate the optimality of our corresponding APLSs. For other OptDGPs, we establish conditional lower bounds that exploit the sequential efficiency of the verifier alone (under the assumption that NP ≠ co-NP) or that of both the verifier and the prover (under the assumption that P ≠ NP, with and without the unique games conjecture).
Cite as
Yuval Emek and Yuval Gil. Twenty-Two New Approximate Proof Labeling Schemes. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 20:1-20:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{emek_et_al:LIPIcs.DISC.2020.20,
author = {Emek, Yuval and Gil, Yuval},
title = {{Twenty-Two New Approximate Proof Labeling Schemes}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {20:1--20:14},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.20},
URN = {urn:nbn:de:0030-drops-130983},
doi = {10.4230/LIPIcs.DISC.2020.20},
annote = {Keywords: proof labeling schemes, distributed graph problems, approximation algorithms}
}
Document
Distributed Constructions of Dual-Failure Fault-Tolerant Distance Preservers
Abstract
Fault tolerant distance preservers (spanners) are sparse subgraphs that preserve (approximate) distances between given pairs of vertices under edge or vertex failures. So-far, these structures have been studied thoroughly mainly from a centralized viewpoint. Despite the fact fault tolerant preservers are mainly motivated by the error-prone nature of distributed networks, not much is known on the distributed computational aspects of these structures.
In this paper, we present distributed algorithms for constructing fault tolerant distance preservers and +2 additive spanners that are resilient to at most two edge faults. Prior to our work, the only non-trivial constructions known were for the single fault and single source setting by [Ghaffari and Parter SPAA'16].
Our key technical contribution is a distributed algorithm for computing distance preservers w.r.t. a subset S of source vertices, resilient to two edge faults. The output structure contains a BFS tree BFS(s,G ⧵ {e₁,e₂}) for every s ∈ S and every e₁,e₂ ∈ G. The distributed construction of this structure is based on a delicate balance between the edge congestion (formed by running multiple BFS trees simultaneously) and the sparsity of the output subgraph. No sublinear-round algorithms for constructing these structures have been known before.
Cite as
Merav Parter. Distributed Constructions of Dual-Failure Fault-Tolerant Distance Preservers. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 21:1-21:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{parter:LIPIcs.DISC.2020.21,
author = {Parter, Merav},
title = {{Distributed Constructions of Dual-Failure Fault-Tolerant Distance Preservers}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {21:1--21:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.21},
URN = {urn:nbn:de:0030-drops-130992},
doi = {10.4230/LIPIcs.DISC.2020.21},
annote = {Keywords: Fault Tolerance, Distance Preservers, CONGEST}
}
Document
Singularly Optimal Randomized Leader Election
Abstract
This paper concerns designing distributed algorithms that are singularly optimal, i.e., algorithms that are simultaneously time and message optimal, for the fundamental leader election problem in networks. Our main result is a randomized distributed leader election algorithm for asynchronous complete networks that is essentially (up to a polylogarithmic factor) singularly optimal. Our algorithm uses O(n) messages with high probability and runs in O(log² n) time (with high probability) to elect a unique leader. The O(n) message complexity should be contrasted with the Ω(n log n) lower bounds for the deterministic message complexity of leader election algorithms (regardless of time), proven by Korach, Moran, and Zaks (TCS, 1989) for asynchronous algorithms and by Afek and Gafni (SIAM J. Comput., 1991) for synchronous networks. Hence, our result also separates the message complexities of randomized and deterministic leader election. More importantly, our (randomized) time complexity of O(log² n) for obtaining the optimal O(n) message complexity is significantly smaller than the long-standing Θ̃(n) time complexity obtained by Afek and Gafni and by Singh (SIAM J. Comput., 1997) for message optimal (deterministic) election in asynchronous networks. Afek and Gafni also conjectured that Θ̃(n) time would be optimal for message-optimal asynchronous algorithms. Our result shows that randomized algorithms are significantly faster.
Turning to synchronous complete networks, Afek and Gafni showed an essentially singularly optimal deterministic algorithm with O(log n) time and O(n log n) messages. Ramanathan et al. (Distrib. Comput. 2007) used randomization to improve the message complexity, and showed a randomized algorithm with O(n) messages but still with O(log n) time (with failure probability O(1 / log^{Ω(1)}n)). Our second result shows that synchronous complete networks admit a tightly singularly optimal randomized algorithm, with O(1) time and O(n) messages (both bounds are optimal). Moreover, our algorithm’s time bound holds with certainty, and its message bound holds with high probability, i.e., 1-1/n^c for constant c.
Our results demonstrate that leader election can be solved in a simultaneously message and time-efficient manner in asynchronous complete networks using randomization. It is open whether this is possible in asynchronous general networks.
Cite as
Shay Kutten, William K. Moses Jr., Gopal Pandurangan, and David Peleg. Singularly Optimal Randomized Leader Election. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 22:1-22:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{kutten_et_al:LIPIcs.DISC.2020.22,
author = {Kutten, Shay and Moses Jr., William K. and Pandurangan, Gopal and Peleg, David},
title = {{Singularly Optimal Randomized Leader Election}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {22:1--22:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.22},
URN = {urn:nbn:de:0030-drops-131002},
doi = {10.4230/LIPIcs.DISC.2020.22},
annote = {Keywords: Leader election, Asynchronous systems, Randomized algorithms, Singularly optimal, Complete networks}
}
Document
Making Byzantine Consensus Live
Abstract
Partially synchronous Byzantine consensus protocols typically structure their execution into a sequence of views, each with a designated leader process. The key to guaranteeing liveness in these protocols is to ensure that all correct processes eventually overlap in a view with a correct leader for long enough to reach a decision. We propose a simple view synchronizer abstraction that encapsulates the corresponding functionality for Byzantine consensus protocols, thus simplifying their design. We present a formal specification of a view synchronizer and its implementation under partial synchrony, which runs in bounded space despite tolerating message loss during asynchronous periods. We show that our synchronizer specification is strong enough to guarantee liveness for single-shot versions of several well-known Byzantine consensus protocols, including HotStuff, Tendermint, PBFT and SBFT. We furthermore give precise latency bounds for these protocols when using our synchronizer. By factoring out the functionality of view synchronization we are able to specify and analyze the protocols in a uniform framework, which allows comparing them and highlights trade-offs.
Cite as
Manuel Bravo, Gregory Chockler, and Alexey Gotsman. Making Byzantine Consensus Live. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 23:1-23:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{bravo_et_al:LIPIcs.DISC.2020.23,
author = {Bravo, Manuel and Chockler, Gregory and Gotsman, Alexey},
title = {{Making Byzantine Consensus Live}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {23:1--23:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.23},
URN = {urn:nbn:de:0030-drops-131013},
doi = {10.4230/LIPIcs.DISC.2020.23},
annote = {Keywords: Byzantine consensus, blockchain, partial synchrony, liveness}
}
Document
Leaderless State-Machine Replication: Specification, Properties, Limits
Abstract
Modern Internet services commonly replicate critical data across several geographical locations using state-machine replication (SMR). Due to their reliance on a leader replica, classical SMR protocols offer limited scalability and availability in this setting. To solve this problem, recent protocols follow instead a leaderless approach, in which each replica is able to make progress using a quorum of its peers. In this paper, we study this new emerging class of SMR protocols and states some of their limits. We first propose a framework that captures the essence of leaderless state-machine replication (Leaderless SMR). Then, we introduce a set of desirable properties for these protocols: (R)eliability, (O)ptimal (L)atency and (L)oad Balancing. We show that protocols matching all of the ROLL properties are subject to a trade-off between performance and reliability. We also establish a lower bound on the message delay to execute a command in protocols optimal for the ROLL properties. This lower bound explains the persistent chaining effect observed in experimental results.
Cite as
Tuanir França Rezende and Pierre Sutra. Leaderless State-Machine Replication: Specification, Properties, Limits. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 24:1-24:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{francarezende_et_al:LIPIcs.DISC.2020.24,
author = {Fran\c{c}a Rezende, Tuanir and Sutra, Pierre},
title = {{Leaderless State-Machine Replication: Specification, Properties, Limits}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {24:1--24:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.24},
URN = {urn:nbn:de:0030-drops-131024},
doi = {10.4230/LIPIcs.DISC.2020.24},
annote = {Keywords: Fault Tolerance, State Machine Replication, Consensus}
}
Document
Not a COINcidence: Sub-Quadratic Asynchronous Byzantine Agreement WHP
Abstract
King and Saia were the first to break the quadratic word complexity bound for Byzantine Agreement in synchronous systems against an adaptive adversary, and Algorand broke this bound with near-optimal resilience (first in the synchronous model and then with eventual-synchrony). Yet the question of asynchronous sub-quadratic Byzantine Agreement remained open. To the best of our knowledge, we are the first to answer this question in the affirmative. A key component of our solution is a shared coin algorithm based on a VRF. A second essential ingredient is VRF-based committee sampling, which we formalize and utilize in the asynchronous model for the first time. Our algorithms work against a delayed-adaptive adversary, which cannot perform after-the-fact removals but has full control of Byzantine processes and full information about communication in earlier rounds. Using committee sampling and our shared coin, we solve Byzantine Agreement with high probability, with a word complexity of Õ(n) and O(1) expected time, breaking the O(n²) bit barrier for asynchronous Byzantine Agreement.
Cite as
Shir Cohen, Idit Keidar, and Alexander Spiegelman. Not a COINcidence: Sub-Quadratic Asynchronous Byzantine Agreement WHP. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 25:1-25:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{cohen_et_al:LIPIcs.DISC.2020.25,
author = {Cohen, Shir and Keidar, Idit and Spiegelman, Alexander},
title = {{Not a COINcidence: Sub-Quadratic Asynchronous Byzantine Agreement WHP}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {25:1--25:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.25},
URN = {urn:nbn:de:0030-drops-131034},
doi = {10.4230/LIPIcs.DISC.2020.25},
annote = {Keywords: shared coin, Byzantine Agreement, VRF, sub-quadratic consensus protocol}
}
Document
Expected Linear Round Synchronization: The Missing Link for Linear Byzantine SMR
Abstract
State Machine Replication (SMR) solutions often divide time into rounds, with a designated leader driving decisions in each round. Progress is guaranteed once all correct processes synchronize to the same round, and the leader of that round is correct. Recently suggested Byzantine SMR solutions such as HotStuff, Tendermint, and LibraBFT achieve progress with a linear message complexity and a constant time complexity once such round synchronization occurs. But round synchronization itself incurs an additional cost. By Dolev and Reischuk’s lower bound, any deterministic solution must have Ω(n²) communication complexity. Yet the question of randomized round synchronization with an expected linear message complexity remained open.
We present an algorithm that, for the first time, achieves round synchronization with expected linear message complexity and expected constant latency. Existing protocols can use our round synchronization algorithm to solve Byzantine SMR with the same asymptotic performance.
Cite as
Oded Naor and Idit Keidar. Expected Linear Round Synchronization: The Missing Link for Linear Byzantine SMR. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 26:1-26:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{naor_et_al:LIPIcs.DISC.2020.26,
author = {Naor, Oded and Keidar, Idit},
title = {{Expected Linear Round Synchronization: The Missing Link for Linear Byzantine SMR}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {26:1--26:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.26},
URN = {urn:nbn:de:0030-drops-131046},
doi = {10.4230/LIPIcs.DISC.2020.26},
annote = {Keywords: Distributed Systems, State Machine Replication}
}
Document
Asynchronous Reconfiguration with Byzantine Failures
Abstract
Replicated services are inherently vulnerable to failures and security breaches. In a long-running system, it is, therefore, indispensable to maintain a reconfiguration mechanism that would replace faulty replicas with correct ones. An important challenge is to enable reconfiguration without affecting the availability and consistency of the replicated data: the clients should be able to get correct service even when the set of service replicas is being updated.
In this paper, we address the problem of reconfiguration in the presence of Byzantine failures: faulty replicas or clients may arbitrarily deviate from their expected behavior. We describe a generic technique for building asynchronous and Byzantine fault-tolerant reconfigurable objects: clients can manipulate the object data and issue reconfiguration calls without reaching consensus on the current configuration. With the help of forward-secure digital signatures, our solution makes sure that superseded and possibly compromised configurations are harmless, that slow clients cannot be fooled into reading stale data, and that Byzantine clients cannot cause a denial of service by flooding the system with reconfiguration requests. Our approach is modular and based on dynamic lattice agreement abstraction, and we discuss how to extend it to enable Byzantine fault-tolerant implementations of a large class of reconfigurable replicated services.
Cite as
Petr Kuznetsov and Andrei Tonkikh. Asynchronous Reconfiguration with Byzantine Failures. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 27:1-27:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{kuznetsov_et_al:LIPIcs.DISC.2020.27,
author = {Kuznetsov, Petr and Tonkikh, Andrei},
title = {{Asynchronous Reconfiguration with Byzantine Failures}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {27:1--27:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.27},
URN = {urn:nbn:de:0030-drops-131054},
doi = {10.4230/LIPIcs.DISC.2020.27},
annote = {Keywords: Reconfiguration, Asynchronous Models, Byzantine Faults}
}
Document
Improved Extension Protocols for Byzantine Broadcast and Agreement
Abstract
Byzantine broadcast (BB) and Byzantine agreement (BA) are two most fundamental problems and essential building blocks in distributed computing, and improving their efficiency is of interest to both theoreticians and practitioners. In this paper, we study extension protocols of BB and BA, i.e., protocols that solve BB/BA with long inputs of l bits using lower costs than l single-bit instances. We present new protocols with improved communication complexity in almost all settings: authenticated BA/BB with t < n/2, authenticated BB with t < (1-ε)n, unauthenticated BA/BB with t < n/3, and asynchronous reliable broadcast and BA with t < n/3. The new protocols are advantageous and significant in several aspects. First, they achieve the best-possible communication complexity of Θ(nl) for wider ranges of input sizes compared to prior results. Second, the authenticated extension protocols achieve optimal communication complexity given the current best available BB/BA protocols for short messages. Third, to the best of our knowledge, our asynchronous and authenticated protocols in the setting are the first extension protocols in that setting.
Cite as
Kartik Nayak, Ling Ren, Elaine Shi, Nitin H. Vaidya, and Zhuolun Xiang. Improved Extension Protocols for Byzantine Broadcast and Agreement. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 28:1-28:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{nayak_et_al:LIPIcs.DISC.2020.28,
author = {Nayak, Kartik and Ren, Ling and Shi, Elaine and Vaidya, Nitin H. and Xiang, Zhuolun},
title = {{Improved Extension Protocols for Byzantine Broadcast and Agreement}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {28:1--28:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.28},
URN = {urn:nbn:de:0030-drops-131064},
doi = {10.4230/LIPIcs.DISC.2020.28},
annote = {Keywords: Byzantine agreement, Byzantine broadcast, extension protocol, communication complexity}
}
Document
From Partial to Global Asynchronous Reliable Broadcast
Abstract
Broadcast is a fundamental primitive in distributed computing. It allows a sender to consistently distribute a message among n recipients. The seminal result of Pease et al. [JACM'80] shows that in a complete network of synchronous bilateral channels, broadcast is achievable if and only if the number of corruptions is bounded by t < n/3. To overcome this bound, a fascinating line of works, Fitzi and Maurer [STOC'00], Considine et al. [JC'05], and Raykov [ICALP'15], proposed strengthening the communication network by assuming partial synchronous broadcast channels, which guarantee consistency among a subset of recipients.
We extend this line of research to the asynchronous setting. We consider reliable broadcast protocols assuming a communication network which provides each subset of b parties with reliable broadcast channels. A natural question is to investigate the trade-off between the size b and the corruption threshold t. We answer this question by showing feasibility and impossibility results:
- A reliable broadcast protocol Π_{RBC} that:
- For 3 ≤ b ≤ 4, is secure up to t < n/2 corruptions.
- For b > 4 even, is secure up to t < ((b-4)/(b-2) n + 8/(b-2)) corruptions.
- For b > 4 odd, is secure up to t < ((b-3)/(b-1) n + 6/(b-1)) corruptions.
- A nonstop reliable broadcast Π_{nRBC}, where parties are guaranteed to obtain output as in reliable broadcast but may need to run forever, secure up to t < (b-1)/(b+1) n corruptions.
- There is no protocol for (nonstop) reliable broadcast secure up to t ≥ (b-1)/(b+1) n corruptions, implying that Π_{RBC} is an asymptotically optimal reliable broadcast protocol, and Π_{nRBC} is an optimal nonstop reliable broadcast protocol.
Cite as
Diana Ghinea, Martin Hirt, and Chen-Da Liu-Zhang. From Partial to Global Asynchronous Reliable Broadcast. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 29:1-29:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{ghinea_et_al:LIPIcs.DISC.2020.29,
author = {Ghinea, Diana and Hirt, Martin and Liu-Zhang, Chen-Da},
title = {{From Partial to Global Asynchronous Reliable Broadcast}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {29:1--29:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.29},
URN = {urn:nbn:de:0030-drops-131074},
doi = {10.4230/LIPIcs.DISC.2020.29},
annote = {Keywords: asynchronous broadcast, partial broadcast}
}
Document
Fast Agreement in Networks with Byzantine Nodes
Abstract
We study Consensus in synchronous networks with arbitrary connected topologies. Nodes may be faulty, in the sense of either Byzantine or proneness to crashing. Let t denote a known upper bound on the number of faulty nodes, and D_s denote a maximum diameter of a network obtained by removing up to s nodes, assuming the network is (s+1)-connected. We give an algorithm for Consensus running in time t + D_{2t} with nodes subject to Byzantine faults. We show that, for any algorithm solving Consensus for Byzantine nodes, there is a network G and an execution of the algorithm on this network that takes Ω(t + D_{2t}) rounds. We give an algorithm solving Consensus in t + D_{t} communication rounds with Byzantine nodes using authenticated messages of polynomial size. We show that for any numbers t and d > 4, there exists a network G and an algorithm solving Consensus with Byzantine nodes using authenticated messages in fewer than t + 3 rounds on G, but all algorithms solving Consensus without message authentication require at least t + d rounds on G. This separates Consensus with Byzantine nodes from Consensus with Byzantine nodes using message authentication, with respect to asymptotic time performance in networks of arbitrary connected topologies, which is unlike complete networks. Let f denote the number of failures actually occurring in an execution and unknown to the nodes. We develop an algorithm solving Consensus against crash failures and running in time 𝒪(f + D_{f}), assuming only that nodes know their names and can differentiate among ports; this algorithm is also communication-efficient, by using messages of size 𝒪(mlog n), where n is the number of nodes and m is the number of edges. We give a lower bound t+D_t-2 on the running time of any deterministic solution to Consensus in (t+1)-connected networks, if t nodes may crash.
Cite as
Bogdan S. Chlebus, Dariusz R. Kowalski, and Jan Olkowski. Fast Agreement in Networks with Byzantine Nodes. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 30:1-30:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{chlebus_et_al:LIPIcs.DISC.2020.30,
author = {Chlebus, Bogdan S. and Kowalski, Dariusz R. and Olkowski, Jan},
title = {{Fast Agreement in Networks with Byzantine Nodes}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {30:1--30:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.30},
URN = {urn:nbn:de:0030-drops-131088},
doi = {10.4230/LIPIcs.DISC.2020.30},
annote = {Keywords: distributed algorithm, network, Consensus, Byzantine fault, message authentication, node crash, lower bound}
}
Document
Scalable and Secure Computation Among Strangers: Message-Competitive Byzantine Protocols
Abstract
The last decade has seen substantial progress on designing Byzantine agreement algorithms which do not require all-to-all communication. However, these protocols do require each node to play a particular role determined by its ID. Motivated by the rise of permissionless systems such as Bitcoin, where nodes can join and leave at will, we extend this research to a more practical model where initially, each node does not know the identity of its neighbors. In particular, a node can send to new destinations only by sending to random (or arbitrary) nodes, or responding to messages received from those destinations. We assume a synchronous and fully-connected network, with a full-information, but static Byzantine adversary. A major drawback of existing Byzantine protocols in this setting is that they have at least Ω(n²) message complexity, where n is the total number of nodes. In particular, the communication cost incurred by the honest nodes is Ω(n²), even when Byzantine node send no messages. In this paper, we design protocols for fundamental problems which are message-competitive, i.e., the total number of bits sent by honest nodes is not significantly more than the total sent by Byzantine nodes.
We describe a message-competitive algorithm to solve Byzantine agreement, leader election, and committee election. Our algorithm sends an expected O((T+n)log n) bits and has latency O(polylog(n)) (even in the CONGEST model), where T = O(n²) is the number of bits sent by Byzantine nodes. The algorithm is resilient to (1/4-ε)n Byzantine nodes for any fixed ε > 0, and succeeds with high probability. Our message bounds are essentially optimal up to polylagarithmic factors, for algorithms that run in polylogarithmic rounds in the CONGEST model.
We also show lower bounds for message-competitive Byzantine agreement regardless of rounds. We prove that, in general, one cannot hope to design Byzantine protocols that have communication cost that is significantly smaller than the cost of the Byzantine adversary.
Cite as
John Augustine, Valerie King, Anisur Rahaman Molla, Gopal Pandurangan, and Jared Saia. Scalable and Secure Computation Among Strangers: Message-Competitive Byzantine Protocols. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 31:1-31:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{augustine_et_al:LIPIcs.DISC.2020.31,
author = {Augustine, John and King, Valerie and Molla, Anisur Rahaman and Pandurangan, Gopal and Saia, Jared},
title = {{Scalable and Secure Computation Among Strangers: Message-Competitive Byzantine Protocols}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {31:1--31:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.31},
URN = {urn:nbn:de:0030-drops-131093},
doi = {10.4230/LIPIcs.DISC.2020.31},
annote = {Keywords: Byzantine protocols, Byzantine agreement, Leader election, Committee election, Message-competitive protocol, Randomized protocol}
}
Document
Byzantine Lattice Agreement in Synchronous Message Passing Systems
Abstract
We propose three algorithms for the Byzantine lattice agreement problem in synchronous systems. The first algorithm runs in min {3h(X) + 6,6√{f_a} + 6}) rounds and takes O(n² min{h(X), √{f_a}}) messages, where h(X) is the height of the input lattice X, n is the total number of processes in the system, f is the maximum number of Byzantine processes such that n ≥ 3f + 1 and f_a ≤ f is the actual number of Byzantine processes in an execution. The second algorithm takes 3log n + 3 rounds and O(n² log n) messages. The third algorithm takes 4 log f + 3 rounds and O(n² log f) messages. All algorithms can tolerate f < n/3 Byzantine failures. This is the first work for the Byzantine lattice agreement problem in synchronous systems which achieves logarithmic rounds. In our algorithms, we apply a slightly modified version of the Gradecast algorithm given by Feldman et al [Feldman and Micali, 1988] as a building block. If we use the Gradecast algorithm for authenticated setting given by Katz et al [Katz and Koo, 2006], we obtain algorithms for the Byzantine lattice agreement problem in authenticated settings and tolerate f < n/2 failures.
Cite as
Xiong Zheng and Vijay Garg. Byzantine Lattice Agreement in Synchronous Message Passing Systems. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 32:1-32:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{zheng_et_al:LIPIcs.DISC.2020.32,
author = {Zheng, Xiong and Garg, Vijay},
title = {{Byzantine Lattice Agreement in Synchronous Message Passing Systems}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {32:1--32:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.32},
URN = {urn:nbn:de:0030-drops-131106},
doi = {10.4230/LIPIcs.DISC.2020.32},
annote = {Keywords: Lattice agreement, Byzantine Failure, Gradecast}
}
Document
Fast Distributed Algorithms for Girth, Cycles and Small Subgraphs
Abstract
In this paper we give fast distributed graph algorithms for detecting and listing small subgraphs, and for computing or approximating the girth. Our algorithms improve upon the state of the art by polynomial factors, and for girth, we obtain a constant-time algorithm for additive +1 approximation in Congested Clique, and the first parametrized algorithm for exact computation in Congest.
In the Congested Clique model, we first develop a technique for learning small neighborhoods, and apply it to obtain an O(1)-round algorithm that computes the girth with only an additive +1 error. Next, we introduce a new technique (the partition tree technique) allowing for efficiently listing all copies of any subgraph, which is deterministic and improves upon the state-of the-art for non-dense graphs. We give two concrete applications of the partition tree technique: First we show that for constant k, it is possible to solve C_{2k}-detection in O(1) rounds in the Congested Clique, improving on prior work, which used fast matrix multiplication and thus had polynomial round complexity. Second, we show that in triangle-free graphs, the girth can be exactly computed in time polynomially faster than the best known bounds for general graphs. We remark that no analogous result is currently known for sequential algorithms.
In the Congest model, we describe a new approach for finding cycles, and instantiate it in two ways: first, we show a fast parametrized algorithm for girth with round complexity Õ(min{g⋅ n^{1-1/Θ(g)},n}) for any girth g; and second, we show how to find small even-length cycles C_{2k} for k = 3,4,5 in O(n^{1-1/k}) rounds. This is a polynomial improvement upon the previous running times; for example, our C₆-detection algorithm runs in O(n^{2/3}) rounds, compared to O(n^{3/4}) in prior work. Finally, using our improved C₆-freeness algorithm, and the barrier on proving lower bounds on triangle-freeness of Eden et al., we show that improving the current ̃Ω(√n) lower bound for C₆-freeness of Korhonen et al. by any polynomial factor would imply strong circuit complexity lower bounds.
Cite as
Keren Censor-Hillel, Orr Fischer, Tzlil Gonen, François Le Gall, Dean Leitersdorf, and Rotem Oshman. Fast Distributed Algorithms for Girth, Cycles and Small Subgraphs. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 33:1-33:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{censorhillel_et_al:LIPIcs.DISC.2020.33,
author = {Censor-Hillel, Keren and Fischer, Orr and Gonen, Tzlil and Le Gall, Fran\c{c}ois and Leitersdorf, Dean and Oshman, Rotem},
title = {{Fast Distributed Algorithms for Girth, Cycles and Small Subgraphs}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {33:1--33:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.33},
URN = {urn:nbn:de:0030-drops-131115},
doi = {10.4230/LIPIcs.DISC.2020.33},
annote = {Keywords: distributed graph algorithms, cycles, girth, Congested Clique, CONGEST}
}
Document
Improved MPC Algorithms for MIS, Matching, and Coloring on Trees and Beyond
Abstract
We present O(log log n) round scalable Massively Parallel Computation algorithms for maximal independent set and maximal matching, in trees and more generally graphs of bounded arboricity, as well as for coloring trees with a constant number of colors. Following the standards, by a scalable MPC algorithm, we mean that these algorithms can work on machines that have capacity/memory as small as n^{δ} for any positive constant δ < 1. Our results improve over the O(log²log n) round algorithms of Behnezhad et al. [PODC'19]. Moreover, our matching algorithm is presumably optimal as its bound matches an Ω(log log n) conditional lower bound of Ghaffari, Kuhn, and Uitto [FOCS'19].
Cite as
Mohsen Ghaffari, Christoph Grunau, and Ce Jin. Improved MPC Algorithms for MIS, Matching, and Coloring on Trees and Beyond. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 34:1-34:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{ghaffari_et_al:LIPIcs.DISC.2020.34,
author = {Ghaffari, Mohsen and Grunau, Christoph and Jin, Ce},
title = {{Improved MPC Algorithms for MIS, Matching, and Coloring on Trees and Beyond}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {34:1--34:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.34},
URN = {urn:nbn:de:0030-drops-131128},
doi = {10.4230/LIPIcs.DISC.2020.34},
annote = {Keywords: Massively Parallel Computation, MIS, Matching, Coloring}
}
Document
Improved Distributed Approximations for Maximum Independent Set
Abstract
We present improved results for approximating maximum-weight independent set (MaxIS) in the CONGEST and LOCAL models of distributed computing. Given an input graph, let n and Δ be the number of nodes and maximum degree, respectively, and let MIS(n,Δ) be the running time of finding a maximal independent set (MIS) in the CONGEST model. Bar-Yehuda et al. [PODC 2017] showed that there is an algorithm in the CONGEST model that finds a Δ-approximation for MaxIS in O(MIS(n,Δ)log W) rounds, where W is the maximum weight of a node in the graph, which can be as large as poly (n). Whether their algorithm is deterministic or randomized that succeeds with high probability depends on the MIS algorithm that is used as a black-box. Our results:
1) A deterministic O(MIS(n,Δ)/ε)-round algorithm that finds a (1+ε)Δ-approximation for MaxIS in the CONGEST model.
2) A randomized (poly(log log n)/ε)-round algorithm that finds, with high probability, a (1+ε)Δ-approximation for MaxIS in the CONGEST model. That is, by sacrificing only a tiny fraction of the approximation guarantee, we achieve an exponential speed-up in the running time over the previous best known result.
3) A randomized O(log n⋅ poly(log log n)/ε)-round algorithm that finds, with high probability, a 8(1+ε)α-approximation for MaxIS in the CONGEST model, where α is the arboricity of the graph. For graphs of arboricity α < Δ/(8(1+ε)), this result improves upon the previous best known result in both the approximation factor and the running time.
One may wonder whether it is possible to approximate MaxIS with high probability in fewer than poly(log log n) rounds. Interestingly, a folklore randomized ranking algorithm by Boppana implies a single round algorithm that gives an expected Δ-approximation in the CONGEST model. However, it is unclear how to convert this algorithm to one that succeeds with high probability without sacrificing a large number of rounds. For unweighted graphs of maximum degree Δ ≤ n/log n, we show a new analysis of the randomized ranking algorithm, which we combine with the local-ratio technique, to provide a O(1/ε)-round algorithm in the CONGEST model that, with high probability, finds an independent set of size at least n/((1+ε)(Δ+1)). This result cannot be extended to very high degree graphs, as we show a lower bound of Ω(log^*n) rounds for any randomized algorithm that with probability at least 1-1/log n finds an independent set of size Ω(n/Δ). This lower bound holds even for the LOCAL model. The hard instances that we use to prove our lower bound are graphs of maximum degree Δ = Ω(n/log^*n).
Cite as
Ken-ichi Kawarabayashi, Seri Khoury, Aaron Schild, and Gregory Schwartzman. Improved Distributed Approximations for Maximum Independent Set. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 35:1-35:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{kawarabayashi_et_al:LIPIcs.DISC.2020.35,
author = {Kawarabayashi, Ken-ichi and Khoury, Seri and Schild, Aaron and Schwartzman, Gregory},
title = {{Improved Distributed Approximations for Maximum Independent Set}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {35:1--35:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.35},
URN = {urn:nbn:de:0030-drops-131135},
doi = {10.4230/LIPIcs.DISC.2020.35},
annote = {Keywords: Distributed graph algorithms, Approximation algorithms, Lower bounds}
}
Document
Models of Smoothing in Dynamic Networks
Abstract
Smoothed analysis is a framework suggested for mediating gaps between worst-case and average-case complexities. In a recent work, Dinitz et al. [Distributed Computing, 2018] suggested to use smoothed analysis in order to study dynamic networks. Their aim was to explain the gaps between real-world networks that function well despite being dynamic, and the strong theoretical lower bounds for arbitrary networks. To this end, they introduced a basic model of smoothing in dynamic networks, where an adversary picks a sequence of graphs, representing the topology of the network over time, and then each of these graphs is slightly perturbed in a random manner.
The model suggested above is based on a per-round noise, and our aim in this work is to extend it to models of noise more suited for multiple rounds. This is motivated by long-lived networks, where the amount and location of noise may vary over time. To this end, we present several different models of noise. First, we extend the previous model to cases where the amount of noise is very small. Then, we move to more refined models, where the amount of noise can change between different rounds, e.g., as a function of the number of changes the network undergoes. We also study a model where the noise is not arbitrarily spread among the network, but focuses in each round in the areas where changes have occurred. Finally, we study the power of an adaptive adversary, who can choose its actions in accordance with the changes that have occurred so far. We use the flooding problem as a running case-study, presenting very different behaviors under the different models of noise, and analyze the flooding time in different models.
Cite as
Uri Meir, Ami Paz, and Gregory Schwartzman. Models of Smoothing in Dynamic Networks. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 36:1-36:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{meir_et_al:LIPIcs.DISC.2020.36,
author = {Meir, Uri and Paz, Ami and Schwartzman, Gregory},
title = {{Models of Smoothing in Dynamic Networks}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {36:1--36:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.36},
URN = {urn:nbn:de:0030-drops-131145},
doi = {10.4230/LIPIcs.DISC.2020.36},
annote = {Keywords: Distributed dynamic graph algorithms, Smoothed analysis, Flooding}
}
Document
Distributed Maximum Matching Verification in CONGEST
Abstract
We study the maximum cardinality matching problem in a standard distributed setting, where the nodes V of a given n-node network graph G = (V,E) communicate over the edges E in synchronous rounds. More specifically, we consider the distributed CONGEST model, where in each round, each node of G can send an O(log n)-bit message to each of its neighbors. We show that for every graph G and a matching M of G, there is a randomized CONGEST algorithm to verify M being a maximum matching of G in time O(|M|) and disprove it in time O(D + 𝓁), where D is the diameter of G and 𝓁 is the length of a shortest augmenting path. We hope that our algorithm constitutes a significant step towards developing a CONGEST algorithm to compute a maximum matching in time Õ(s^*), where s^* is the size of a maximum matching.
Cite as
Mohamad Ahmadi and Fabian Kuhn. Distributed Maximum Matching Verification in CONGEST. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 37:1-37:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{ahmadi_et_al:LIPIcs.DISC.2020.37,
author = {Ahmadi, Mohamad and Kuhn, Fabian},
title = {{Distributed Maximum Matching Verification in CONGEST}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {37:1--37:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.37},
URN = {urn:nbn:de:0030-drops-131151},
doi = {10.4230/LIPIcs.DISC.2020.37},
annote = {Keywords: distributed matching, distributed graph algorithms, augmenting paths}
}
Document
Distributed Planar Reachability in Nearly Optimal Time
Abstract
We present nearly optimal distributed algorithms for fundamental reachability problems in planar graphs. In the single-source reachability problem given is an n-vertex directed graph G = (V,E) and a source node s, it is required to determine the subset of nodes that are reachable from s in G. We present the first distributed reachability algorithm for planar graphs that runs in nearly optimal time of Õ(D) rounds, where D is the undirected diameter of the graph. This improves the complexity of Õ(D²) rounds implied by the recent work of [Li and Parter, STOC'19].
We also consider the more general reachability problem of identifying the strongly connected components (SCCs) of the graph. We present an Õ(D)-round algorithm that computes for each node in the graph an identifier of its strongly connected component in G. No non-trivial upper bound for this problem (even in general graphs) has been known before.
Our algorithms are based on characterizing the structural interactions between balanced cycle separators. We show that the reachability relations between separator nodes can be compressed due to a Monge-like property of their directed shortest paths. The algorithmic results are obtained by combining this structural characterization with the recursive graph partitioning machinery of [Li and Parter, STOC'19].
Cite as
Merav Parter. Distributed Planar Reachability in Nearly Optimal Time. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 38:1-38:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{parter:LIPIcs.DISC.2020.38,
author = {Parter, Merav},
title = {{Distributed Planar Reachability in Nearly Optimal Time}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {38:1--38:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.38},
URN = {urn:nbn:de:0030-drops-131160},
doi = {10.4230/LIPIcs.DISC.2020.38},
annote = {Keywords: Distributed Graph Algorithms, Planar Graphs, Reachability}
}
Document
Coloring Fast Without Learning Your Neighbors' Colors
Abstract
We give an improved randomized CONGEST algorithm for distance-2 coloring that uses Δ²+1 colors and runs in O(log n) rounds, improving the recent O(log Δ ⋅ log n)-round algorithm in [Halldórsson, Kuhn, Maus; PODC '20]. We then improve the time complexity to O(log Δ) + 2^{O(√{log log n})}.
Cite as
Magnús M. Halldórsson, Fabian Kuhn, Yannic Maus, and Alexandre Nolin. Coloring Fast Without Learning Your Neighbors' Colors. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 39:1-39:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{halldorsson_et_al:LIPIcs.DISC.2020.39,
author = {Halld\'{o}rsson, Magn\'{u}s M. and Kuhn, Fabian and Maus, Yannic and Nolin, Alexandre},
title = {{Coloring Fast Without Learning Your Neighbors' Colors}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {39:1--39:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.39},
URN = {urn:nbn:de:0030-drops-131170},
doi = {10.4230/LIPIcs.DISC.2020.39},
annote = {Keywords: distributed graph coloring, distance 2 coloring, congestion}
}
Document
Brief Announcement
Brief Announcement: Efficient Load-Balancing Through Distributed Token Dropping
Abstract
We introduce a new graph problem, the token dropping game, and we show how to solve it efficiently in a distributed setting. We use the token dropping game as a tool to design an efficient distributed algorithm for the stable orientation problem, which is a special case of the more general locally optimal semi-matching problem. The prior work by Czygrinow et al. (DISC 2012) finds a locally optimal semi-matching in O(Δ⁵) rounds in graphs of maximum degree Δ, which directly implies an algorithm with the same runtime for stable orientations. We improve the runtime to O(Δ⁴) for stable orientations and prove a lower bound of Ω(Δ) rounds.
Cite as
Sebastian Brandt, Barbara Keller, Joel Rybicki, Jukka Suomela, and Jara Uitto. Brief Announcement: Efficient Load-Balancing Through Distributed Token Dropping. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 40:1-40:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{brandt_et_al:LIPIcs.DISC.2020.40,
author = {Brandt, Sebastian and Keller, Barbara and Rybicki, Joel and Suomela, Jukka and Uitto, Jara},
title = {{Brief Announcement: Efficient Load-Balancing Through Distributed Token Dropping}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {40:1--40:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.40},
URN = {urn:nbn:de:0030-drops-131182},
doi = {10.4230/LIPIcs.DISC.2020.40},
annote = {Keywords: distributed algorithms, graph problems, semi-matching}
}
Document
Brief Announcement
Brief Announcement: Distributed Graph Problems Through an Automata-Theoretic Lens
Abstract
We study the following algorithm synthesis question: given the description of a locally checkable graph problem Π for paths or cycles, determine in which instances Π is solvable, determine what is the locality of Π, and construct an asymptotically optimal distributed algorithm for solving Π (in the usual LOCAL model of distributed computing). To answer such questions, we represent Π as a nondeterministic finite automaton ℳ over a unary alphabet, and identify polynomial-time-computable properties of automaton ℳ that capture the locality and solvability of problem Π.
Cite as
Yi-Jun Chang, Jan Studený, and Jukka Suomela. Brief Announcement: Distributed Graph Problems Through an Automata-Theoretic Lens. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 41:1-41:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{chang_et_al:LIPIcs.DISC.2020.41,
author = {Chang, Yi-Jun and Studen\'{y}, Jan and Suomela, Jukka},
title = {{Brief Announcement: Distributed Graph Problems Through an Automata-Theoretic Lens}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {41:1--41:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.41},
URN = {urn:nbn:de:0030-drops-131197},
doi = {10.4230/LIPIcs.DISC.2020.41},
annote = {Keywords: Algorithm synthesis, locally checkable labeling problems, LOCAL model, locality, distributed computational complexity, nondeterministic finite automata}
}
Document
Brief Announcement
Brief Announcement: Phase Transitions of the k-Majority Dynamics in a Biased Communication Model
Abstract
We analyze the binary-state (either ℛ or ℬ) k-majority dynamics in a biased communication model where nodes have some fixed probability p, independent of the dynamics, of being seen in state ℬ by their neighbors. In this setting we study how p, as well as the initial unbalance between the two states, impact on the speed of convergence of the process, identifying sharp phase transitions.
Cite as
Emilio Cruciani, Hlafo Alfie Mimun, Matteo Quattropani, and Sara Rizzo. Brief Announcement: Phase Transitions of the k-Majority Dynamics in a Biased Communication Model. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 42:1-42:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{cruciani_et_al:LIPIcs.DISC.2020.42,
author = {Cruciani, Emilio and Mimun, Hlafo Alfie and Quattropani, Matteo and Rizzo, Sara},
title = {{Brief Announcement: Phase Transitions of the k-Majority Dynamics in a Biased Communication Model}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {42:1--42:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.42},
URN = {urn:nbn:de:0030-drops-131200},
doi = {10.4230/LIPIcs.DISC.2020.42},
annote = {Keywords: Biased Communication, Consensus, Majority Dynamics, Markov Chains, Metastability}
}
Document
Brief Announcement
Brief Announcement: Distributed Quantum Proofs for Replicated Data
Abstract
This paper tackles the issue of checking that all copies of a large data set replicated at several nodes of a network are identical. The fact that the replicas may be located at distant nodes prevents the system from verifying their equality locally, i.e., by having each node consult only nodes in its vicinity. On the other hand, it remains possible to assign certificates to the nodes, so that verifying the consistency of the replicas can be achieved locally. However, we show that, as the replicated data is large, classical certification mechanisms, including distributed Merlin-Arthur protocols, cannot guarantee good completeness and soundness simultaneously, unless they use very large certificates. The main result of this paper is a distributed quantum Merlin-Arthur protocol enabling the nodes to collectively check the consistency of the replicas, based on small certificates, and in a single round of message exchange between neighbors, with short messages. In particular, the certificate-size is logarithmic in the size of the data set, which gives an exponential advantage over classical certification mechanisms.
Cite as
Pierre Fraigniaud, François Le Gall, Harumichi Nishimura, and Ami Paz. Brief Announcement: Distributed Quantum Proofs for Replicated Data. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 43:1-43:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{fraigniaud_et_al:LIPIcs.DISC.2020.43,
author = {Fraigniaud, Pierre and Le Gall, Fran\c{c}ois and Nishimura, Harumichi and Paz, Ami},
title = {{Brief Announcement: Distributed Quantum Proofs for Replicated Data}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {43:1--43:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.43},
URN = {urn:nbn:de:0030-drops-131217},
doi = {10.4230/LIPIcs.DISC.2020.43},
annote = {Keywords: Quantum Computing, Distributed Network Computing, Algorithmic Aspects of Networks}
}
Document
Brief Announcement
Brief Announcement: Optimally-Resilient Unconditionally-Secure Asynchronous Multi-Party Computation Revisited
Abstract
In this paper, we present an optimally-resilient, unconditionally-secure asynchronous multi-party computation (AMPC) protocol for n parties, tolerating a computationally unbounded adversary, capable of corrupting up to t < n/3 parties. Our protocol needs a communication of 𝒪(n⁴) field elements per multiplication gate. This is to be compared with previous best AMPC protocol (Patra et al, ICITS 2009) in the same setting, which needs a communication of 𝒪(n⁵) field elements per multiplication gate. To design our protocol, we present a simple and highly efficient asynchronous verifiable secret-sharing (AVSS) protocol, which is of independent interest.
Cite as
Ashish Choudhury. Brief Announcement: Optimally-Resilient Unconditionally-Secure Asynchronous Multi-Party Computation Revisited. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 44:1-44:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{choudhury:LIPIcs.DISC.2020.44,
author = {Choudhury, Ashish},
title = {{Brief Announcement: Optimally-Resilient Unconditionally-Secure Asynchronous Multi-Party Computation Revisited}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {44:1--44:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.44},
URN = {urn:nbn:de:0030-drops-131223},
doi = {10.4230/LIPIcs.DISC.2020.44},
annote = {Keywords: Verifiable Secret-sharing, Secure MPC, Fault-tolerance, Byzantine faults, secret-sharing, unconditional-security, privacy}
}
Document
Brief Announcement
Brief Announcement: Polygraph: Accountable Byzantine Agreement
Abstract
In this paper, we introduce Polygraph, the first accountable Byzantine consensus algorithm. If among n users f < n/3 are malicious then it ensures consensus, otherwise it eventually detects malicious users that cause disagreement. Polygraph is appealing for blockchains as it allows to totally order blocks in a chain whenever possible, hence avoiding double spending and, otherwise, to punish at least n/3 malicious users when a fork occurs. This problem is more difficult than it first appears. Blockchains typically run in open networks whose delays are hard to predict, hence one cannot build upon synchronous techniques [Andreas Haeberlen et al., 2007; Vitalik Buterin and Virgil Griffith, 2019]. One may exploit cryptographic evidence of PBFT-like consensus [Miguel Castro and Barbara Liskov, 2002], however detecting equivocation would be insufficient. We show that it is impossible without extra logs of at least Ω(n) rounds [Pierre Civit et al., 2019]. Each round of Polygraph exchanges O(n²) messages.
Cite as
Pierre Civit, Seth Gilbert, and Vincent Gramoli. Brief Announcement: Polygraph: Accountable Byzantine Agreement. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 45:1-45:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{civit_et_al:LIPIcs.DISC.2020.45,
author = {Civit, Pierre and Gilbert, Seth and Gramoli, Vincent},
title = {{Brief Announcement: Polygraph: Accountable Byzantine Agreement}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {45:1--45:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.45},
URN = {urn:nbn:de:0030-drops-131236},
doi = {10.4230/LIPIcs.DISC.2020.45},
annote = {Keywords: Fault detection, cryptography, equivocation, consensus}
}
Document
Brief Announcement
Brief Announcement: What Can(Not) Be Perfectly Rerouted Locally
Abstract
In order to provide a high resilience and to react quickly to link failures, modern computer networks support fully decentralized flow rerouting, also known as local fast failover. In a nutshell, the task of a local fast failover algorithm is to pre-define fast failover rules for each node using locally available information only. Ideally, such a local fast failover algorithm provides a perfect resilience deterministically: a packet emitted from any source can reach any target, as long as the underlying network remains connected. Feigenbaum et al. showed [Feigenbaum and others, 2012] that it is not always possible to provide perfect resilience; on the positive side, the authors also presented an efficient algorithm which achieves at least 1-resilience, tolerating a single failure in any network.
Interestingly, not much more is known currently about the feasibility of perfect resilience. This brief announcement revisits perfect resilience with local fast failover, both in a model where the source can and cannot be used for forwarding decisions. By establishing a connection between graph minors and resilience, we prove that it is impossible to achieve perfect resilience on any non-planar graph; On the positive side, we can derive perfect resilience for outerplanar and some planar graphs.
Cite as
Klaus-Tycho Foerster, Juho Hirvonen, Yvonne-Anne Pignolet, Stefan Schmid, and Gilles Tredan. Brief Announcement: What Can(Not) Be Perfectly Rerouted Locally. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 46:1-46:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{foerster_et_al:LIPIcs.DISC.2020.46,
author = {Foerster, Klaus-Tycho and Hirvonen, Juho and Pignolet, Yvonne-Anne and Schmid, Stefan and Tredan, Gilles},
title = {{Brief Announcement: What Can(Not) Be Perfectly Rerouted Locally}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {46:1--46:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.46},
URN = {urn:nbn:de:0030-drops-131244},
doi = {10.4230/LIPIcs.DISC.2020.46},
annote = {Keywords: Resilience, Local Failover}
}
Document
Brief Announcement
Brief Announcement: Byzantine Agreement, Broadcast and State Machine Replication with Optimal Good-Case Latency
Abstract
This paper investigates the problem good-case latency of Byzantine agreement, broadcast and state machine replication in the synchronous authenticated setting. The good-case latency measure captures the time it takes to reach agreement when all non-faulty parties have the same input (or in BB/SMR when the sender/leader is non-faulty) and all messages arrive instantaneously. Previous result implies a lower bound showing that any Byzantine agreement or broadcast protocol tolerating more than n/3 faults must have a good-case latency of at least Δ. Our first result is a matching tight upper bound for a family of protocols we call 1Δ. We propose a protocol 1Δ-BA that solves Byzantine agreement in the synchronous and authenticated setting with optimal good-case latency of Δ and optimal resilience f < n/2. We then extend our protocol and present 1Δ-BB and 1Δ-SMR for Byzantine fault tolerant broadcast and state machine replication, respectively, in the same setting and with the same optimal good-case latency of Δ and f < n/2 fault tolerance.
Cite as
Ittai Abraham, Kartik Nayak, Ling Ren, and Zhuolun Xiang. Brief Announcement: Byzantine Agreement, Broadcast and State Machine Replication with Optimal Good-Case Latency. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 47:1-47:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{abraham_et_al:LIPIcs.DISC.2020.47,
author = {Abraham, Ittai and Nayak, Kartik and Ren, Ling and Xiang, Zhuolun},
title = {{Brief Announcement: Byzantine Agreement, Broadcast and State Machine Replication with Optimal Good-Case Latency}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {47:1--47:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.47},
URN = {urn:nbn:de:0030-drops-131259},
doi = {10.4230/LIPIcs.DISC.2020.47},
annote = {Keywords: Byzantine broadcast, synchrony, latency, state machine replication}
}
Document
Brief Announcement
Brief Announcement: Multi-Threshold Asynchronous Reliable Broadcast and Consensus
Abstract
Classical protocols for reliable broadcast and consensus provide security guarantees as long as the number of corrupted parties f is bounded by a single given threshold t. If f > t, these protocols are completely deemed insecure. We consider the relaxed notion of multi-threshold reliable broadcast and consensus where validity, consistency and termination are guaranteed as long as f ≤ t_v, f ≤ t_c and f ≤ t_t respectively. For consensus, we consider both variants of (1-ε)-consensus and almost-surely terminating consensus, where termination is guaranteed with probability (1-ε) and 1, respectively. We give a very complete characterization for these primitives in the asynchronous setting and with no signatures:
- Multi-threshold reliable broadcast is possible if and only if max{t_c,t_v} + 2t_t < n.
- Multi-threshold almost-surely consensus is possible if max{t_c, t_v} + 2t_t < n, 2t_v + t_t < n and t_t < n/3. Assuming a global coin, it is possible if and only if max{t_c, t_v} + 2t_t < n and 2t_v + t_t < n.
- Multi-threshold (1-ε)-consensus is possible if and only if max{t_c, t_v} + 2t_t < n and 2t_v + t_t < n.
Cite as
Martin Hirt, Ard Kastrati, and Chen-Da Liu-Zhang. Brief Announcement: Multi-Threshold Asynchronous Reliable Broadcast and Consensus. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 48:1-48:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{hirt_et_al:LIPIcs.DISC.2020.48,
author = {Hirt, Martin and Kastrati, Ard and Liu-Zhang, Chen-Da},
title = {{Brief Announcement: Multi-Threshold Asynchronous Reliable Broadcast and Consensus}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {48:1--48:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.48},
URN = {urn:nbn:de:0030-drops-131267},
doi = {10.4230/LIPIcs.DISC.2020.48},
annote = {Keywords: broadcast, byzantine agreement, multi-threshold}
}
Document
Brief Announcement
Brief Announcement: Game Theoretical Framework for Analyzing Blockchains Robustness
Abstract
Blockchains systems evolve in complex environments that mix classical patterns of faults (e.g crash faults, transient faults, Byzantine faults, churn) with selfish, rational or irrational behaviors typical to economical systems. In this paper we propose a game theoretical framework in order to formally characterize the robustness of blockchains systems in terms of resilience to rational deviations and immunity to Byzantine behaviors. Our framework includes necessary and sufficient conditions for checking the immunity and resilience of games and a new technique for composing games that preserves the robustness of individual games. We prove the practical interest of our formal framework by characterizing the robustness of three different protocols popular in blockchain systems: a HTLC-based payment scheme (a.k.a. Lightning Network), a side-chain protocol and a cross-chain swap protocol.
Cite as
Paolo Zappalà, Marianna Belotti, Maria Potop-Butucaru, and Stefano Secci. Brief Announcement: Game Theoretical Framework for Analyzing Blockchains Robustness. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 49:1-49:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{zappala_et_al:LIPIcs.DISC.2020.49,
author = {Zappal\`{a}, Paolo and Belotti, Marianna and Potop-Butucaru, Maria and Secci, Stefano},
title = {{Brief Announcement: Game Theoretical Framework for Analyzing Blockchains Robustness}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {49:1--49:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.49},
URN = {urn:nbn:de:0030-drops-131275},
doi = {10.4230/LIPIcs.DISC.2020.49},
annote = {Keywords: Blockchains, Game Theory, Byzantine-Altruistic-Rational behaviours}
}
Document
Brief Announcement
Brief Announcement: Jiffy: A Fast, Memory Efficient, Wait-Free Multi-Producers Single-Consumer Queue
Abstract
In applications such as sharded data processing systems, data flow programming and load sharing applications, multiple concurrent data producers are feeding requests into the same data consumer. This can be naturally realized through concurrent queues, where each consumer pulls its tasks from its dedicated queue. For scalability, wait-free queues are often preferred over lock based structures.
The vast majority of wait-free queue implementations, and even lock-free ones, support the multi-producer multi-consumer model. Yet, this comes at a premium, since implementing wait-free multi-producer multi-consumer queues requires utilizing complex helper data structures. The latter increases the memory consumption of such queues and limits their performance and scalability. Additionally, many such designs employ (hardware) cache unfriendly memory access patterns.
In this work we study the implementation of wait-free multi-producer single-consumer queues. Specifically, we propose Jiffy, an efficient memory frugal novel wait-free multi-producer single-consumer queue and formally prove its correctness. We then compare the performance and memory requirements of Jiffy with other state of the art lock-free and wait-free queues. We show that indeed Jiffy can maintain good performance with up to 128 threads, delivers better throughput than other constructions we compared against, and consumes less memory.
Cite as
Dolev Adas and Roy Friedman. Brief Announcement: Jiffy: A Fast, Memory Efficient, Wait-Free Multi-Producers Single-Consumer Queue. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 50:1-50:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{adas_et_al:LIPIcs.DISC.2020.50,
author = {Adas, Dolev and Friedman, Roy},
title = {{Brief Announcement: Jiffy: A Fast, Memory Efficient, Wait-Free Multi-Producers Single-Consumer Queue}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {50:1--50:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.50},
URN = {urn:nbn:de:0030-drops-131287},
doi = {10.4230/LIPIcs.DISC.2020.50},
annote = {Keywords: Wait-freedom, MPSC Queues, Concurrent data-structures}
}
Document
Brief Announcement
Brief Announcement: Concurrent Fixed-Size Allocation and Free in Constant Time
Abstract
We describe an algorithm for supporting allocation and free for fixed-sized blocks, for p asynchronous processors, with O(1) worst-case time per operation, Θ(p²) additive space overhead, and using only single-word read, write, and CAS. While many algorithms rely on having constant-time fixed-size allocate and free, we present the first implementation of these two operations that is constant time with reasonable space overhead.
Cite as
Guy E. Blelloch and Yuanhao Wei. Brief Announcement: Concurrent Fixed-Size Allocation and Free in Constant Time. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 51:1-51:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{blelloch_et_al:LIPIcs.DISC.2020.51,
author = {Blelloch, Guy E. and Wei, Yuanhao},
title = {{Brief Announcement: Concurrent Fixed-Size Allocation and Free in Constant Time}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {51:1--51:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.51},
URN = {urn:nbn:de:0030-drops-131291},
doi = {10.4230/LIPIcs.DISC.2020.51},
annote = {Keywords: malloc, free, fixed-size, concurrent, constant time}
}
Document
Brief Announcement
Brief Announcement: Building Fast Recoverable Persistent Data Structures with Montage
Abstract
The recent emergence of fast, dense, nonvolatile main memory suggests that certain long-lived data structures might remain in their natural, pointer-rich format across program runs and hardware reboots. Operations on such structures must be instrumented with explicit write-back and fence instructions to ensure consistency in the wake of a crash. Techniques to minimize the cost of this instrumentation are an active topic of current research.
We present what we believe to be the first general-purpose approach to building buffered durably linearizable persistent data structures, and a system, Montage, to support that approach. Montage is built on top of the Ralloc nonblocking persistent allocator. It employs a slow-ticking epoch clock, and ensures that no operation appears to span an epoch boundary. If a crash occurs in epoch e, all work performed in epochs e and e-1 is lost, but all work from prior epochs is preserved.
We describe the implementation of Montage, argue its correctness, and report on experiments confirming excellent performance for operations on queues, sets/mappings, and general graphs.
Cite as
Haosen Wen, Wentao Cai, Mingzhe Du, Benjamin Valpey, and Michael L. Scott. Brief Announcement: Building Fast Recoverable Persistent Data Structures with Montage. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 52:1-52:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{wen_et_al:LIPIcs.DISC.2020.52,
author = {Wen, Haosen and Cai, Wentao and Du, Mingzhe and Valpey, Benjamin and Scott, Michael L.},
title = {{Brief Announcement: Building Fast Recoverable Persistent Data Structures with Montage}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {52:1--52:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.52},
URN = {urn:nbn:de:0030-drops-131304},
doi = {10.4230/LIPIcs.DISC.2020.52},
annote = {Keywords: Durable linearizability, consistency, persistence, fault tolerance}
}
Document
Brief Announcement
Brief Announcement: Reaching Approximate Consensus When Everyone May Crash
Abstract
Fault-tolerant consensus is of great importance in distributed systems. This paper studies the asynchronous approximate consensus problem in the crash-recovery model with fair-loss links. In our model, up to f nodes may crash forever, while the rest may crash intermittently. Each node is equipped with a limited-size persistent storage that does not lose data when crashed. We present an algorithm that only stores three values in persistent storage - state, phase index, and a counter.
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Lewis Tseng, Qinzi Zhang, and Yifan Zhang. Brief Announcement: Reaching Approximate Consensus When Everyone May Crash. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 53:1-53:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{tseng_et_al:LIPIcs.DISC.2020.53,
author = {Tseng, Lewis and Zhang, Qinzi and Zhang, Yifan},
title = {{Brief Announcement: Reaching Approximate Consensus When Everyone May Crash}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {53:1--53:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.53},
URN = {urn:nbn:de:0030-drops-131319},
doi = {10.4230/LIPIcs.DISC.2020.53},
annote = {Keywords: Approximate Consensus, Fair-loss Channel, Crash-recovery}
}
Document
Brief Announcement
Brief Announcement: On Decidability of 2-Process Affine Models
Abstract
Affine models of computation, defined as subsets of iterated immediate-snapshot runs, capture a wide variety of shared-memory systems: wait-freedom, t-resilience, k-concurrency, and fair shared-memory adversaries. The question of whether a given task is solvable in a given affine model is, in general, undecidable.
In this paper, we focus on affine models defined for a system of two processes. We show that task computability of 2-process affine models is decidable and presents a complete hierarchy of five equivalence classes of 2-process affine models.
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Petr Kuznetsov and Thibault Rieutord. Brief Announcement: On Decidability of 2-Process Affine Models. In 34th International Symposium on Distributed Computing (DISC 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 179, pp. 54:1-54:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)
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@InProceedings{kuznetsov_et_al:LIPIcs.DISC.2020.54,
author = {Kuznetsov, Petr and Rieutord, Thibault},
title = {{Brief Announcement: On Decidability of 2-Process Affine Models}},
booktitle = {34th International Symposium on Distributed Computing (DISC 2020)},
pages = {54:1--54:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-168-9},
ISSN = {1868-8969},
year = {2020},
volume = {179},
editor = {Attiya, Hagit},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2020.54},
URN = {urn:nbn:de:0030-drops-131328},
doi = {10.4230/LIPIcs.DISC.2020.54},
annote = {Keywords: Affine tasks, Decidability}
}