Pub Date : 2024-08-17DOI: 10.1007/s00446-024-00471-7
Hossein Naderibeni, Eric Ruppert
We present a novel linearizable wait-free queue implementation using single-word CAS instructions. Previous lock-free queue implementations from CAS all have amortized step complexity of (Omega (p)) per operation in worst-case executions, where p is the number of processes that access the queue. Our new wait-free queue takes (O(log p)) steps per enqueue and (O(log ^2 p +log q)) steps per dequeue, where q is the size of the queue. A bounded-space version of the implementation has (O(log p log (p+q))) amortized step complexity per operation.
我们提出了一种使用单字 CAS 指令实现的新型可线性化无等待队列。CAS 之前的无锁队列实现在最坏情况下的执行中,每次操作的摊销步骤复杂度都是(Omega (p)),其中 p 是访问队列的进程数。我们的新免等待队列每次enqueue需要(O(log p))步,每次dequeue需要(O(log ^2 p +log q))步,其中q是队列的大小。有界空间版本的实现每次操作的摊销步骤复杂度为(O(log p log (p+q))。
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Pub Date : 2024-06-06DOI: 10.1007/s00446-024-00465-5
Xing Hu, Sam Toueg
The implementation of registers from (potentially) weaker registers is a classical problem in the theory of distributed computing. Since Lamport’s pioneering work (Lamport in Distrib Comput 1(2):77–101, 1986), this problem has been extensively studied in the context of asynchronous processes with crash failures. In this paper, we investigate this problem in the context of Byzantine process failures, with and without process signatures. We first prove that, without signatures, there is no wait-free linearizable implementation of a 1-writer n-reader register from atomic 1-writer 1-reader registers. In fact, we show a stronger result, namely, even under the assumption that the writer can only crash and at most one reader can be malicious, there is no linearizable implementation of a 1-writer n-reader register from atomic 1-writer ((n-1))-reader registers that ensures that every correct process eventually completes its operations. In light of this impossibility result, we give two implementations of a 1-writer n-reader register from atomic 1-writer 1-reader registers that work under different assumptions. The first implementation is linearizable (under any combination of Byzantine process failures), but it guarantees that every correct process eventually completes its operations only under the assumption that the writer is correct or no reader is Byzantine—thus matching the impossibility result. The second implementation assumes process signatures; it is wait-free and linearizable under any number and combination of Byzantine process failures.
从(可能)较弱的寄存器实现寄存器是分布式计算理论中的一个经典问题。自 Lamport 的开创性工作(Lamport in Distrib Comput 1(2):77-101,1986)以来,这个问题已在具有崩溃故障的异步进程中得到广泛研究。在本文中,我们将在有进程签名和无进程签名的拜占庭进程故障背景下研究这个问题。我们首先证明,在没有签名的情况下,不存在由原子 1 写 1 读寄存器实现的 1 写 n 读寄存器的无等待线性化实现。事实上,我们证明了一个更强的结果,即即使假设写入器只能崩溃,且最多只有一个读取器可能是恶意的,也不存在由原子1-写入器((n-1))-读取器寄存器组成的1-写入器n-读取器寄存器的可线性化实现,以确保每个正确的进程最终都能完成操作。根据这个不可能结果,我们给出了两个由原子 1 写 1 读寄存器实现的 1 写 n 读寄存器,它们在不同的假设条件下工作。第一种实现是可线性化的(在拜占庭进程失败的任何组合下),但它保证每个正确的进程最终只在写入器正确或没有读取器拜占庭的假设下完成其操作,因此与不可能结果相匹配。第二种实现假定有进程签名;在拜占庭进程失败的任何数量和组合下,它都是无等待和可线性化的。
{"title":"On implementing SWMR registers from SWSR registers in systems with Byzantine failures","authors":"Xing Hu, Sam Toueg","doi":"10.1007/s00446-024-00465-5","DOIUrl":"https://doi.org/10.1007/s00446-024-00465-5","url":null,"abstract":"<p>The implementation of registers from (potentially) weaker registers is a classical problem in the theory of distributed computing. Since Lamport’s pioneering work (Lamport in Distrib Comput 1(2):77–101, 1986), this problem has been extensively studied in the context of asynchronous processes with crash failures. In this paper, we investigate this problem in the context of Byzantine process failures, with and without process signatures. We first prove that, without signatures, there is no wait-free linearizable implementation of a 1-writer <i>n</i>-reader register from atomic 1-writer 1-reader registers. In fact, we show a stronger result, namely, even under the assumption that the writer can only crash and at most one reader can be malicious, there is no linearizable implementation of a 1-writer <i>n</i>-reader register from atomic 1-writer <span>((n-1))</span>-reader registers that ensures that every correct process eventually completes its operations. In light of this impossibility result, we give two implementations of a 1-writer <i>n</i>-reader register from atomic 1-writer 1-reader registers that work under different assumptions. The first implementation is linearizable (under any combination of Byzantine process failures), but it guarantees that every correct process eventually completes its operations only under the assumption that the writer is correct or no reader is Byzantine—thus matching the impossibility result. The second implementation assumes process signatures; it is wait-free and linearizable under any number and combination of Byzantine process failures.\u0000</p>","PeriodicalId":50569,"journal":{"name":"Distributed Computing","volume":"40 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141549333","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-01Epub Date: 2022-04-05DOI: 10.1017/ipm.2022.10
J Surdey, D Byrne, T Fox
This article focuses on the development of Ireland's first National Student Mental Health and Suicide Prevention Framework for Higher Education. There is growing concern for student mental health in higher education nationally and globally. The majority of students are aged between 18 and 24, which is identified as a high-risk group for mental health difficulties. Recent surveys of student mental illness, mental distress, and low well-being have been recognized by the World Health Organization, the Union of Students in Ireland National Report on Student Mental Health in Third Level Education, the My World survey and the My World 2 study. The Higher Education Authority in Ireland made a commitment to the Department of Health Connecting for Life (Ireland's National Strategy to Reduce Suicide 2015-2020) to form national guidelines for suicide prevention in higher education. In order to deliver on this commitment, The National Student Mental Health and Suicide Prevention Framework was developed. The Framework is informed by international evidence and was the product of a collaborative cross sector and cross disciplinary team including health professionals, government representatives, educators, students, policy makers, community organizations, researchers and clinicians.
{"title":"Developing Irelands first National Student Mental Health and Suicide Prevention Framework for Higher Education.","authors":"J Surdey, D Byrne, T Fox","doi":"10.1017/ipm.2022.10","DOIUrl":"10.1017/ipm.2022.10","url":null,"abstract":"<p><p>This article focuses on the development of Ireland's first National Student Mental Health and Suicide Prevention Framework for Higher Education. There is growing concern for student mental health in higher education nationally and globally. The majority of students are aged between 18 and 24, which is identified as a high-risk group for mental health difficulties. Recent surveys of student mental illness, mental distress, and low well-being have been recognized by the World Health Organization, the Union of Students in Ireland National Report on Student Mental Health in Third Level Education, the My World survey and the My World 2 study. The Higher Education Authority in Ireland made a commitment to the Department of Health Connecting for Life (Ireland's National Strategy to Reduce Suicide 2015-2020) to form national guidelines for suicide prevention in higher education. In order to deliver on this commitment, The National Student Mental Health and Suicide Prevention Framework was developed. The Framework is informed by international evidence and was the product of a collaborative cross sector and cross disciplinary team including health professionals, government representatives, educators, students, policy makers, community organizations, researchers and clinicians.</p>","PeriodicalId":50569,"journal":{"name":"Distributed Computing","volume":"1 1","pages":"254-258"},"PeriodicalIF":1.8,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89836997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-28DOI: 10.1007/s00446-024-00469-1
Orestis Alpos, Christian Cachin, Björn Tackmann, Luca Zanolini
Quorum systems are a key abstraction in distributed fault-tolerant computing for capturing trust assumptions. They can be found at the core of many algorithms for implementing reliable broadcasts, shared memory, consensus and other problems. This paper introduces asymmetric Byzantine quorum systems that model subjective trust. Every process is free to choose which combinations of other processes it trusts and which ones it considers faulty. Asymmetric quorum systems strictly generalize standard Byzantine quorum systems, which have only one global trust assumption for all processes. This work also presents protocols that implement abstractions of shared memory, broadcast primitives, and a consensus protocol among processes prone to Byzantine faults and asymmetric trust. The model and protocols pave the way for realizing more elaborate algorithms with asymmetric trust.
{"title":"Asymmetric distributed trust","authors":"Orestis Alpos, Christian Cachin, Björn Tackmann, Luca Zanolini","doi":"10.1007/s00446-024-00469-1","DOIUrl":"https://doi.org/10.1007/s00446-024-00469-1","url":null,"abstract":"<p>Quorum systems are a key abstraction in distributed fault-tolerant computing for capturing trust assumptions. They can be found at the core of many algorithms for implementing reliable broadcasts, shared memory, consensus and other problems. This paper introduces <i>asymmetric Byzantine quorum systems</i> that model subjective trust. Every process is free to choose which combinations of other processes it trusts and which ones it considers faulty. Asymmetric quorum systems strictly generalize standard Byzantine quorum systems, which have only one global trust assumption for all processes. This work also presents protocols that implement abstractions of shared memory, broadcast primitives, and a consensus protocol among processes prone to Byzantine faults and asymmetric trust. The model and protocols pave the way for realizing more elaborate algorithms with asymmetric trust.\u0000</p>","PeriodicalId":50569,"journal":{"name":"Distributed Computing","volume":"48 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2024-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141165449","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-03DOI: 10.1007/s00446-024-00466-4
Manuel Bravo, Gregory Chockler, Alexey Gotsman
Byzantine state-machine replication (SMR) ensures the consistency of replicated state in the presence of malicious replicas and lies at the heart of the modern blockchain technology. Byzantine SMR protocols often guarantee safety under all circumstances and liveness only under synchrony. However, guaranteeing liveness even under this assumption is nontrivial. So far we have lacked systematic ways of incorporating liveness mechanisms into Byzantine SMR protocols, which often led to subtle bugs. To close this gap, we introduce a modular framework to facilitate the design of provably live and efficient Byzantine SMR protocols. Our framework relies on a view abstraction generated by a special SMR synchronizer primitive to drive the agreement on command ordering. We present a simple formal specification of an SMR synchronizer and its bounded-space implementation under partial synchrony. We also apply our specification to prove liveness and analyze the latency of three Byzantine SMR protocols via a uniform methodology. In particular, one of these results yields what we believe is the first rigorous liveness proof for the algorithmic core of the seminal PBFT protocol.
{"title":"Liveness and latency of Byzantine state-machine replication","authors":"Manuel Bravo, Gregory Chockler, Alexey Gotsman","doi":"10.1007/s00446-024-00466-4","DOIUrl":"https://doi.org/10.1007/s00446-024-00466-4","url":null,"abstract":"<p>Byzantine state-machine replication (SMR) ensures the consistency of replicated state in the presence of malicious replicas and lies at the heart of the modern blockchain technology. Byzantine SMR protocols often guarantee safety under all circumstances and liveness only under synchrony. However, guaranteeing liveness even under this assumption is nontrivial. So far we have lacked systematic ways of incorporating liveness mechanisms into Byzantine SMR protocols, which often led to subtle bugs. To close this gap, we introduce a modular framework to facilitate the design of provably live and efficient Byzantine SMR protocols. Our framework relies on a <i>view</i> abstraction generated by a special <i>SMR synchronizer</i> primitive to drive the agreement on command ordering. We present a simple formal specification of an SMR synchronizer and its bounded-space implementation under partial synchrony. We also apply our specification to prove liveness and analyze the latency of three Byzantine SMR protocols via a uniform methodology. In particular, one of these results yields what we believe is the first rigorous liveness proof for the algorithmic core of the seminal PBFT protocol.\u0000</p>","PeriodicalId":50569,"journal":{"name":"Distributed Computing","volume":"17 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2024-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140886522","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-26DOI: 10.1007/s00446-024-00467-3
Petra Berenbrink, Martin Hoefer, Dominik Kaaser, Pascal Lenzner, Malin Rau, Daniel Schmand
Opinion spreading in a society decides the fate of elections, the success of products, and the impact of political or social movements. A prominent model to study opinion formation processes is due to Hegselmann and Krause. It has the distinguishing feature that stable states do not necessarily show consensus, i.e., the population of agents might not agree on the same opinion. We focus on the social variant of the Hegselmann–Krause model. There are n agents, which are connected by a social network. Their opinions evolve in an iterative, asynchronous process, in which agents are activated one after another at random. When activated, an agent adopts the average of the opinions of its neighbors having a similar opinion (where similarity of opinions is defined using a parameter (varepsilon )). Thus, the set of influencing neighbors of an agent may change over time. We show that such opinion dynamics are guaranteed to converge for any social network. We provide an upper bound of ({text {O}}(n|E|^2 (varepsilon /delta )^2)) on the expected number of opinion updates until convergence to a stable state, where (|E|) is the number of edges of the social network, and (delta ) is a parameter of the stability concept. For the complete social network we show a bound of ({text {O}}(n^3(n^2 + (varepsilon /delta )^2))) that represents a major improvement over the previously best upper bound of ({text {O}}(n^9 (varepsilon /delta )^2)).
{"title":"Asynchronous opinion dynamics in social networks","authors":"Petra Berenbrink, Martin Hoefer, Dominik Kaaser, Pascal Lenzner, Malin Rau, Daniel Schmand","doi":"10.1007/s00446-024-00467-3","DOIUrl":"https://doi.org/10.1007/s00446-024-00467-3","url":null,"abstract":"<p>Opinion spreading in a society decides the fate of elections, the success of products, and the impact of political or social movements. A prominent model to study opinion formation processes is due to Hegselmann and Krause. It has the distinguishing feature that stable states do not necessarily show consensus, i.e., the population of agents might not agree on the same opinion. We focus on the social variant of the Hegselmann–Krause model. There are <i>n</i> agents, which are connected by a social network. Their opinions evolve in an iterative, asynchronous process, in which agents are activated one after another at random. When activated, an agent adopts the average of the opinions of its neighbors having a similar opinion (where similarity of opinions is defined using a parameter <span>(varepsilon )</span>). Thus, the set of influencing neighbors of an agent may change over time. We show that such opinion dynamics are guaranteed to converge for any social network. We provide an upper bound of <span>({text {O}}(n|E|^2 (varepsilon /delta )^2))</span> on the expected number of opinion updates until convergence to a stable state, where <span>(|E|)</span> is the number of edges of the social network, and <span>(delta )</span> is a parameter of the stability concept. For the complete social network we show a bound of <span>({text {O}}(n^3(n^2 + (varepsilon /delta )^2)))</span> that represents a major improvement over the previously best upper bound of <span>({text {O}}(n^9 (varepsilon /delta )^2))</span>.</p>","PeriodicalId":50569,"journal":{"name":"Distributed Computing","volume":"27 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2024-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140806115","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-22DOI: 10.1007/s00446-024-00464-6
Timothé Albouy, Davide Frey, Michel Raynal, François Taïani
This paper considers the good-case latency of Byzantine Reliable Broadcast (BRB), i.e., the time taken by correct processes to deliver a message when the initial sender is correct. This time plays a crucial role in the performance of practical distributed systems. Although significant strides have been made in recent years on this question, progress has mainly focused on either asynchronous or randomized algorithms. By contrast, the good-case latency of deterministic synchronous BRB under a majority of Byzantine faults has been little studied. In particular, it was not known whether a good-case latency below the worst-case bound of (t+1) rounds could be obtained. This work answers this open question positively and proposes a deterministic synchronous Byzantine reliable broadcast that achieves a good-case latency of (textsf{max} (2,t+3-c)) rounds (or equivalently (textsf{max} (2,f+t+3-n))), where t is the upper bound on the number of Byzantine processes, (fle t) the number of effectively Byzantine processes, and (c=n-f) the number of effectively correct processes. The proposed algorithm does not put any constraint on t, and assumes an authenticated setting, in which individual processes can sign the messages they send, and verify the authenticity of the signatures they receive.
本文考虑了拜占庭可靠广播(Byzantine Reliable Broadcast,BRB)的良好情况延迟,即当初始发送者正确时,正确进程传递信息所需的时间。这段时间对实际分布式系统的性能起着至关重要的作用。虽然近年来在这一问题上取得了长足进步,但进展主要集中在异步或随机算法上。相比之下,人们对大多数拜占庭故障下确定性同步 BRB 的良好情况延迟时间研究甚少。尤其是,人们还不知道能否获得低于最坏情况下的(t+1)轮的良好情况下的延迟。这项工作正面回答了这个开放性问题,并提出了一种确定性同步拜占庭可靠广播,它能实现 (textsf{max} (2,t+3-c)) 轮的良好情况下的延迟(或等价于 (textsf{max} (2、t+3-n)),其中 t 是拜占庭进程数量的上限,(fle t )是有效拜占庭进程的数量,(c=n-f )是有效正确进程的数量。所提出的算法对 t 不做任何限制,并假定了一个经过验证的环境,在这个环境中,各个进程可以对它们发送的信息进行签名,并验证它们收到的签名的真实性。
{"title":"Good-case early-stopping latency of synchronous byzantine reliable broadcast: the deterministic case","authors":"Timothé Albouy, Davide Frey, Michel Raynal, François Taïani","doi":"10.1007/s00446-024-00464-6","DOIUrl":"https://doi.org/10.1007/s00446-024-00464-6","url":null,"abstract":"<p>This paper considers the good-case latency of Byzantine Reliable Broadcast (BRB), i.e., the time taken by correct processes to deliver a message when the initial sender is correct. This time plays a crucial role in the performance of practical distributed systems. Although significant strides have been made in recent years on this question, progress has mainly focused on either asynchronous or randomized algorithms. By contrast, the good-case latency of deterministic synchronous BRB under a majority of Byzantine faults has been little studied. In particular, it was not known whether a good-case latency below the worst-case bound of <span>(t+1)</span> rounds could be obtained. This work answers this open question positively and proposes a deterministic synchronous Byzantine reliable broadcast that achieves a good-case latency of <span>(textsf{max} (2,t+3-c))</span> rounds (or equivalently <span>(textsf{max} (2,f+t+3-n))</span>), where <i>t</i> is the upper bound on the number of Byzantine processes, <span>(fle t)</span> the number of effectively Byzantine processes, and <span>(c=n-f)</span> the number of effectively correct processes. The proposed algorithm does not put any constraint on <i>t</i>, and assumes an authenticated setting, in which individual processes can sign the messages they send, and verify the authenticity of the signatures they receive.</p>","PeriodicalId":50569,"journal":{"name":"Distributed Computing","volume":"1 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2024-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140204000","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-22DOI: 10.1007/s00446-024-00462-8
Amos Korman, Robin Vacus
How to efficiently and reliably spread information in a system is one of the most fundamental problems in distributed computing. Recently, inspired by biological scenarios, several works focused on identifying the minimal communication resources necessary to spread information under faulty conditions. Here we study the self-stabilizing bit-dissemination problem, introduced by Boczkowski, Korman, and Natale in [SODA 2017]. The problem considers a fully-connected network of nagents, with a binary world of opinions, one of which is called correct. At any given time, each agent holds an opinion bit as its public output. The population contains a source agent which knows which opinion is correct. This agent adopts the correct opinion and remains with it throughout the execution. We consider the basic (mathcal {PULL}) model of communication, in which each agent observes relatively few randomly chosen agents in each round. The goal of the non-source agents is to quickly converge on the correct opinion, despite having an arbitrary initial configuration, i.e., in a self-stabilizing manner. Once the population converges on the correct opinion, it should remain with it forever. Motivated by biological scenarios in which animals observe and react to the behavior of others, we focus on the extremely constrained model of passive communication, which assumes that when observing another agent the only information that can be extracted is the opinion bit of that agent. We prove that this problem can be solved in a poly-logarithmic in n number of rounds with high probability, while sampling a logarithmic number of agents at each round. Previous works solved this problem faster and using fewer samples, but they did that by decoupling the messages sent by agents from their output opinion, and hence do not fit the framework of passive communication. Moreover, these works use complex recursive algorithms with refined clocks that are unlikely to be used by biological entities. In contrast, our proposed algorithm has a natural appeal as it is based on letting agents estimate the current tendency direction of the dynamics, and then adapt to the emerging trend.
如何在系统中高效可靠地传播信息是分布式计算中最基本的问题之一。最近,受生物场景的启发,有几项研究集中于确定在故障条件下传播信息所需的最小通信资源。在此,我们研究 Boczkowski、Korman 和 Natale 在 [SODA 2017] 中提出的自稳定比特传播问题。该问题考虑了一个由 n 个代理组成的全连接网络,该网络具有二元意见世界,其中一种意见被称为正确意见。在任何给定时间,每个代理都持有一个意见位作为其公共输出。群体中包含一个源代理,它知道哪种观点是正确的。该代理采用正确的观点,并在整个执行过程中保持不变。我们考虑基本的通信模型,即每个代理在每一轮中观察相对较少的随机选择的代理。非源代理的目标是,尽管有一个任意的初始配置,也就是以自稳定的方式,快速收敛到正确的意见上。一旦群体趋同于正确的观点,就应该永远保持下去。受动物观察并对他人行为做出反应的生物场景的启发,我们重点研究了极其受限的被动交流模型,该模型假定当观察另一个代理时,唯一能提取的信息就是该代理的意见位。我们证明,这个问题可以在 n 个回合内以高概率的多对数方式解决,同时在每个回合中对数数量的代理进行采样。以前的研究能以更快的速度和更少的样本解决这个问题,但它们是通过将代理发送的信息与其输出意见解耦来实现的,因此不符合被动通信的框架。此外,这些研究还使用了复杂的递归算法和精制时钟,而生物实体不太可能使用这些算法。相比之下,我们提出的算法则具有天然的吸引力,因为它是基于让代理估计当前的动态趋势方向,然后适应新出现的趋势。
{"title":"Early adapting to trends: self-stabilizing information spread using passive communication","authors":"Amos Korman, Robin Vacus","doi":"10.1007/s00446-024-00462-8","DOIUrl":"https://doi.org/10.1007/s00446-024-00462-8","url":null,"abstract":"<p>How to efficiently and reliably spread information in a system is one of the most fundamental problems in distributed computing. Recently, inspired by biological scenarios, several works focused on identifying the minimal communication resources necessary to spread information under faulty conditions. Here we study the self-stabilizing <i>bit-dissemination</i> problem, introduced by Boczkowski, Korman, and Natale in [SODA 2017]. The problem considers a fully-connected network of <i>n</i> <i>agents</i>, with a binary world of <i>opinions</i>, one of which is called <i>correct</i>. At any given time, each agent holds an opinion bit as its public output. The population contains a <i>source</i> agent which knows which opinion is correct. This agent adopts the correct opinion and remains with it throughout the execution. We consider the basic <span>(mathcal {PULL})</span> model of communication, in which each agent observes relatively few randomly chosen agents in each round. The goal of the non-source agents is to quickly converge on the correct opinion, despite having an arbitrary initial configuration, i.e., in a self-stabilizing manner. Once the population converges on the correct opinion, it should remain with it forever. Motivated by biological scenarios in which animals observe and react to the behavior of others, we focus on the extremely constrained model of <i>passive communication</i>, which assumes that when observing another agent the only information that can be extracted is the opinion bit of that agent. We prove that this problem can be solved in a poly-logarithmic in <i>n</i> number of rounds with high probability, while sampling a logarithmic number of agents at each round. Previous works solved this problem faster and using fewer samples, but they did that by decoupling the messages sent by agents from their output opinion, and hence do not fit the framework of passive communication. Moreover, these works use complex recursive algorithms with refined clocks that are unlikely to be used by biological entities. In contrast, our proposed algorithm has a natural appeal as it is based on letting agents estimate the current tendency direction of the dynamics, and then adapt to the emerging trend.</p>","PeriodicalId":50569,"journal":{"name":"Distributed Computing","volume":"85 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2024-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139945961","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-08DOI: 10.1007/s00446-024-00461-9
Artur Czumaj, Peter Davies-Peck, Merav Parter
In this paper, we study the power and limitations of component-stable algorithms in the low-space model of massively parallel computation (MPC). Recently Ghaffari, Kuhn and Uitto (FOCS 2019) introduced the class of component-stable low-space MPC algorithms, which are, informally, those algorithms for which the outputs reported by the nodes in different connected components are required to be independent. This very natural notion was introduced to capture most (if not all) of the known efficient MPC algorithms to date, and it was the first general class of MPC algorithms for which one can show non-trivial conditional lower bounds. In this paper we enhance the framework of component-stable algorithms and investigate its effect on the complexity of randomized and deterministic low-space MPC. Our key contributions include: 1. We revise and formalize the lifting approach of Ghaffari, Kuhn and Uitto. This requires a very delicate amendment of the notion of component stability, which allows us to fill in gaps in the earlier arguments. 2. We also extend the framework to obtain conditional lower bounds for deterministic algorithms and fine-grained lower bounds that depend on the maximum degree (Delta ). 3. We demonstrate a collection of natural graph problems for which deterministic component-unstable algorithms break the conditional lower bound obtained for component-stable algorithms. This implies that, in the context of deterministic algorithms, component-stable algorithms are conditionally weaker than the component-unstable ones. 4. We also show that the restriction to component-stable algorithms has an impact in the randomized setting. We present a natural problem which can be solved in O(1) rounds by a component-unstable MPC algorithm, but requires (Omega (log log ^* n)) rounds for any component-stable algorithm, conditioned on the connectivity conjecture. Altogether our results imply that component-stability might limit the computational power of the low-space MPC model, at least in certain contexts, paving the way for improved upper bounds that escape the conditional lower bound setting of Ghaffari, Kuhn, and Uitto.
{"title":"Component stability in low-space massively parallel computation","authors":"Artur Czumaj, Peter Davies-Peck, Merav Parter","doi":"10.1007/s00446-024-00461-9","DOIUrl":"https://doi.org/10.1007/s00446-024-00461-9","url":null,"abstract":"<p>In this paper, we study the power and limitations of component-stable algorithms in the low-space model of <i>massively parallel computation (</i><span>MPC</span><i>)</i>. Recently Ghaffari, Kuhn and Uitto (FOCS 2019) introduced the class of <i>component-stable</i> low-space <span>MPC</span> algorithms, which are, informally, those algorithms for which the outputs reported by the nodes in different connected components are required to be independent. This very natural notion was introduced to capture most (if not all) of the known efficient <span>MPC</span> algorithms to date, and it was the first general class of <span>MPC</span> algorithms for which one can show non-trivial conditional lower bounds. In this paper we enhance the framework of component-stable algorithms and investigate its effect on the complexity of randomized and deterministic low-space <span>MPC</span>. Our key contributions include: 1. We revise and formalize the lifting approach of Ghaffari, Kuhn and Uitto. This requires a very delicate amendment of the notion of component stability, which allows us to fill in gaps in the earlier arguments. 2. We also extend the framework to obtain conditional lower bounds for deterministic algorithms and fine-grained lower bounds that depend on the maximum degree <span>(Delta )</span>. 3. We demonstrate a collection of natural graph problems for which deterministic component-unstable algorithms break the conditional lower bound obtained for component-stable algorithms. This implies that, in the context of deterministic algorithms, component-stable algorithms are conditionally weaker than the component-unstable ones. 4. We also show that the restriction to component-stable algorithms has an impact in the randomized setting. We present a natural problem which can be solved in <i>O</i>(1) rounds by a component-unstable <span>MPC</span> algorithm, but requires <span>(Omega (log log ^* n))</span> rounds for any component-stable algorithm, conditioned on the connectivity conjecture. Altogether our results imply that component-stability might limit the computational power of the low-space <span>MPC</span> model, at least in certain contexts, paving the way for improved upper bounds that escape the conditional lower bound setting of Ghaffari, Kuhn, and Uitto.\u0000</p>","PeriodicalId":50569,"journal":{"name":"Distributed Computing","volume":"13 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2024-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139765601","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-01DOI: 10.1007/s00446-024-00460-w
Yehuda Afek, Gal Giladi, Boaz Patt-Shamir
We investigate the effect of omnipresent cloud storage on distributed computing. To this end, we specify a network model with links of prescribed bandwidth that connect standard processing nodes, and, in addition, passive storage nodes. Each passive node represents a cloud storage system, such as Dropbox, Google Drive etc. We study a few tasks in this model, assuming a single cloud node connected to all other nodes, which are connected to each other arbitrarily. We give implementations for basic tasks of collaboratively writing to and reading from the cloud, and for more advanced applications such as matrix multiplication and federated learning. Our results show that utilizing node-cloud links as well as node-node links can considerably speed up computations, compared to the case where processors communicate either only through the cloud or only through the network links. We first show how to optimally read and write large files to and from the cloud in general graphs using flow techniques. We use these primitives to derive algorithms for combining, where every processor node has an input value and the task is to compute a combined value under some given associative operator. In the special but common case of “fat links,” where we assume that links between processors are bidirectional and have high bandwidth, we provide near-optimal algorithms for any commutative combining operator (such as vector addition). For the task of matrix multiplication (or other non-commutative combining operators), where the inputs are ordered, we present tight results in the simple “wheel” network, where procesing nodes are arranged in a ring, and are all connected to a single cloud node.
{"title":"Distributed computing with the cloud","authors":"Yehuda Afek, Gal Giladi, Boaz Patt-Shamir","doi":"10.1007/s00446-024-00460-w","DOIUrl":"https://doi.org/10.1007/s00446-024-00460-w","url":null,"abstract":"<p>We investigate the effect of omnipresent cloud storage on distributed computing. To this end, we specify a network model with links of prescribed bandwidth that connect standard processing nodes, and, in addition, passive storage nodes. Each passive node represents a cloud storage system, such as Dropbox, Google Drive etc. We study a few tasks in this model, assuming a single cloud node connected to all other nodes, which are connected to each other arbitrarily. We give implementations for basic tasks of collaboratively writing to and reading from the cloud, and for more advanced applications such as matrix multiplication and federated learning. Our results show that utilizing node-cloud links as well as node-node links can considerably speed up computations, compared to the case where processors communicate either only through the cloud or only through the network links. We first show how to optimally read and write large files to and from the cloud in general graphs using flow techniques. We use these primitives to derive algorithms for <i>combining</i>, where every processor node has an input value and the task is to compute a combined value under some given associative operator. In the special but common case of “fat links,” where we assume that links between processors are bidirectional and have high bandwidth, we provide near-optimal algorithms for any commutative combining operator (such as vector addition). For the task of matrix multiplication (or other non-commutative combining operators), where the inputs are ordered, we present tight results in the simple “wheel” network, where procesing nodes are arranged in a ring, and are all connected to a single cloud node.</p>","PeriodicalId":50569,"journal":{"name":"Distributed Computing","volume":"61 1","pages":""},"PeriodicalIF":1.3,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139666685","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}