Proceedings of the 39th Symposium on Principles of Distributed Computing最新文献

{"title":"Long-Lived Snapshots with Polylogarithmic Amortized Step Complexity","authors":"Mirza Ahad Baig, Danny Hendler, A. Milani, Corentin Travers","doi":"10.1145/3382734.3406005","DOIUrl":"https://doi.org/10.1145/3382734.3406005","url":null,"abstract":"We present the first deterministic wait-free long-lived snapshot algorithm, using only read and write operations, that guarantees polylogarithmic amortized step complexity in all executions. This is the first non-blocking snapshot algorithm, using reads and writes only, that has sub-linear amortized step complexity in executions of arbitrary length. The key to our construction is a novel implementation of a 2-component max array object which may be of independent interest.","PeriodicalId":222366,"journal":{"name":"Proceedings of the 39th Symposium on Principles of Distributed Computing","volume":"209 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123631954","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lower Bounds for Distributed Sketching of Maximal Matchings and Maximal Independent Sets","authors":"Sepehr Assadi, Gillat Kol, R. Oshman","doi":"10.1145/3382734.3405732","DOIUrl":"https://doi.org/10.1145/3382734.3405732","url":null,"abstract":"Consider the following distributed graph sketching model: There is a referee and n vertices in an undirected graph G sharing public randomness. Each vertex v only knows its neighborhood in G and the referee receives no input initially. The vertices simultaneously each sends a message, called a sketch, to the referee who then based on the received sketches outputs a solution to some combinatorial problem on G, say, the minimum spanning tree problem. Previous work on graph sketching have shown that numerous problems, including connectivity, minimum spanning tree, edge or vertex connectivity, cut or spectral sparsifiers, and (Δ + 1)-vertex coloring, all admit efficient algorithms in this model that only require sketches of size polylog(n) per vertex. In contrast, we prove that the two fundamental problems of maximal matching and maximal independent set do not admit such efficient solutions: Any algorithm for either problem that errs with a small constant probability requires sketches of size Ω(n1/2--ε) for any constant ε > 0. We prove our results by analyzing communication complexity of these problems in a communication model that allows sharing of inputs between limited number of players, and hence lies between the standard number-in-hand and number-on-forehead multi-party communication models. Our proofs are based on a family of hard instances using Ruzsa-Szemerédi graphs and information-theoretic arguments to establish the communication lower bounds.","PeriodicalId":222366,"journal":{"name":"Proceedings of the 39th Symposium on Principles of Distributed Computing","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129726263","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Brief Announcement: Hazard Pointer Protection of Structures with Immutable Links","authors":"Maged M. Michael","doi":"10.1145/3382734.3405738","DOIUrl":"https://doi.org/10.1145/3382734.3405738","url":null,"abstract":"The hazard pointer method [4] for safe reclamation is capable of protecting individual dynamic objects, including individual nodes of linked structures. However, on its own, it does not protect the descendants of protected nodes for unconditional traversal. We present a new algorithm that extends the hazard pointer algorithm to support unconditional traversal though immutable links of acyclic structures. It has an important added advantage of allowing the reclamation of nodes at any depth with their ancestors in the same pass over hazard pointers. Achieving these advantages does not incur any extra computing cost in protection operations, which are the common case. A counter is added to each object for holding the number of inbound immutable links. Such counters are updated when setting and clearing immutable links, which can happen at most once per link in the lifetime of an object. The algorithm is implemented and used in the Facebook Folly open-source C++ library [1].","PeriodicalId":222366,"journal":{"name":"Proceedings of the 39th Symposium on Principles of Distributed Computing","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128010814","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Can Uncoordinated Beeps tell Stories?","authors":"Fabien Dufoulon, J. Burman, J. Beauquier","doi":"10.1145/3382734.3405699","DOIUrl":"https://doi.org/10.1145/3382734.3405699","url":null,"abstract":"The beeping model is an extremely restrictive communication model. Nodes communicate in discrete rounds using beeps---simple bursts of energy---and carrier sensing. Simultaneous beeps produce (nondestructive) collisions, resulting in information loss. Such communication differs greatly from the traditional communication mechanisms in distributed systems, like message-passing or shared memory. Indeed, a beep is a unary signal that communicates no information (e.g., no message content, nor sender information) beyond its own presence. As a result, in a round of beeping communication, hearing a beep means only that some (unknown) neighboring node is communicating in this very round, whereas silence (i.e., hearing no beeps) means only that no neighboring node is communicating. Most previous works assume that nodes all start (wake up) at the same time. In this (synchronous starts) setting nodes have synchronized local clocks and thus synchronized round numbers. Via these round numbers, information can be extrinsically conveyed in a round of beeping communication. For example, the parity of the round number allows to convey letters in {0, 1}. In contrast, we consider here that nodes start in an uncoordinated manner. Thus two nodes may have arbitrarily different round numbers and no information can be extrinsically conveyed in a single round. In the present paper, we show how non-trivial information---e.g., letters from a binary alphabet---can be conveyed through several rounds instead. Applying tools from coding theory and additive number theory, we propose communication schemes---binary words of length l specifying how a node communicates during l consecutive rounds---allowing nodes to convey letters from an alphabet of size h, for any constant h ≥ 2 (known by all nodes). Direct application of such schemes allows to implement a message-passing primitive with an exponential (in the number of message bits) multiplicative overhead. Here, in contrast, we design an exponentially more efficient message-passing primitive. First, we use these communication schemes to implement a 2-hop beep communication primitive, simulating beeping communication on the square of the communication graph. Building upon this primitive, we present the first solution to the 2-hop desynchronization problem in the beeping model with uncoordinated starts. This is a fundamental interference control problem, in which nodes must compute (periodic) infinite communication schemes, disjoint from those chosen by the nodes at distance one and two on the communication graph (thus, the schemes are said to be 2-hop desynchronized). That way, nodes may communicate while avoiding collisions and information loss. Finally, we show how nodes can use these 2-hop desynchronized schemes to simulate a convenient, general (i.e., not limited to any predefined alphabet size h) and efficient (i.e., with an overhead linear in the number of bits of the message) message-passing abstraction layer.","PeriodicalId":222366,"journal":{"name":"Proceedings of the 39th Symposium on Principles of Distributed Computing","volume":"53 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122089591","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Brief Announcement: Why Extension-Based Proofs Fail","authors":"Dan Alistarh, J. Aspnes, Faith Ellen, Rati Gelashvili, Leqi Zhu","doi":"10.1145/3382734.3405743","DOIUrl":"https://doi.org/10.1145/3382734.3405743","url":null,"abstract":"We introduce extension-based proofs, a class of impossibility proofs that includes valency arguments. They are modelled as an interaction between a prover and a protocol. Using proofs based on combinatorial topology, it has been shown that it is impossible to deterministically solve k-set agreement among n > k ≥ 2 processes in a wait-free manner. However, it was unknown whether proofs based on simpler techniques were possible. We explain why this impossibility result cannot be obtained by an extension-based proof and, hence, extension-based proofs are limited in power.","PeriodicalId":222366,"journal":{"name":"Proceedings of the 39th Symposium on Principles of Distributed Computing","volume":"99 1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124179468","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Brief Announcement: Noisy Beeping Networks","authors":"Yagel Ashkenazi, R. Gelles, Amir Leshem","doi":"10.1145/3382734.3405705","DOIUrl":"https://doi.org/10.1145/3382734.3405705","url":null,"abstract":"We introduce noisy beeping networks, where nodes have limited communication capabilities, namely, they can only emit energy or sense the channel for energy. Furthermore, imperfections may cause devices to malfunction with some fixed probability when sensing the channel, which amounts to deducing a noisy received transmission. Such noisy networks have implications for ultra-lightweight sensor networks and biological systems. We show how to compute tasks in a noise-resilient manner over noisy beeping networks of arbitrary structure. In particular, we transform any R-round algorithm that assumes a noiseless beeping network (of size n) into a noise-resilient version while incurring a multiplicative overhead of only O(log n + log R) in its round complexity, with high probability. We show that our coding is optimal for some (short) tasks, such as node-coloring of a clique. We further show how to simulate a large family of algorithms designed for distributed networks in the CONGEST(B) model over a noisy beeping network. The simulation succeeds with high probability and incurs an asymptotic multiplicative overhead of O(B · Δ · min(n, Δ2)) in the round complexity, where Δ is the maximum degree of the network. The overhead is tight for certain graphs, e.g., a clique. Further, this simulation implies a constant overhead coding for constant-degree networks.","PeriodicalId":222366,"journal":{"name":"Proceedings of the 39th Symposium on Principles of Distributed Computing","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127470053","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Brief Announcement: Classification of Distributed Binary Labeling Problems","authors":"A. Balliu, S. Brandt, Yuval Efron, J. Hirvonen, Yannic Maus, D. Olivetti, J. Suomela","doi":"10.1145/3382734.3405703","DOIUrl":"https://doi.org/10.1145/3382734.3405703","url":null,"abstract":"We present a complete classification of the deterministic distributed time complexity for a family of graph problems: binary labeling problems in trees in the usual LOCAL model of distributed computing. 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, and perfect matching. 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. 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.","PeriodicalId":222366,"journal":{"name":"Proceedings of the 39th Symposium on Principles of Distributed Computing","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131198461","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fault-Tolerance in Distributed Optimization: The Case of Redundancy","authors":"Nirupam Gupta, N. Vaidya","doi":"10.1145/3382734.3405748","DOIUrl":"https://doi.org/10.1145/3382734.3405748","url":null,"abstract":"This paper considers the problem of Byzantine fault-tolerance in distributed multi-agent optimization. In this problem, each agent has a local cost function. The goal of a distributed optimization algorithm is to allow the agents to collectively compute a minimum of their aggregate cost function. We consider the case when a certain number of agents may be Byzantine faulty. Such faulty agents may not follow a prescribed algorithm, and they may send arbitrary or incorrect information regarding their local cost functions. Unless a fault-tolerance mechanism is employed, traditional distributed optimization algorithms cannot tolerate such faulty agents. A reasonable goal in presence of faulty agents is to minimize the aggregate cost of the non-faulty agents. However, we show that this goal is impossible to achieve unless the cost functions of the non-faulty agents have a minimal redundancy property. We further propose a distributed optimization algorithm that allows the non-faulty agents to obtain a minimum of their aggregate cost if the minimal redundancy property holds. The scope of our algorithm is demonstrated through distributed sensing and learning applications, which are special cases of distributed optimization.","PeriodicalId":222366,"journal":{"name":"Proceedings of the 39th Symposium on Principles of Distributed Computing","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130911284","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Brief Announcement: Not a COINcidence: Sub-Quadratic Asynchronous Byzantine Agreement WHP","authors":"Shir Cohen, I. Keidar, A. Spiegelman","doi":"10.1145/3382734.3405708","DOIUrl":"https://doi.org/10.1145/3382734.3405708","url":null,"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.","PeriodicalId":222366,"journal":{"name":"Proceedings of the 39th Symposium on Principles of Distributed Computing","volume":"71 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122416025","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Upper and Lower Bounds on the Space Complexity of Detectable Objects","authors":"Ohad Ben-Baruch, Danny Hendler, M. Rusanovsky","doi":"10.1145/3382734.3405725","DOIUrl":"https://doi.org/10.1145/3382734.3405725","url":null,"abstract":"The emergence of systems with non-volatile main memory (NVM) increases the interest in the design of recoverable concurrent objects that are robust to crash-failures, since their operations are able to recover from such failures by using state retained in NVM. Of particular interest are recoverable algorithms that, in addition to ensuring object consistency, also provide detectability, a correctness condition requiring that the recovery code can infer if the failed operation was linearized or not and, in the former case, obtain its response. In this work, we investigate the space complexity of detectable algorithms and the external support they require. We make the following three contributions. First, we present the first wait-free bounded-space detectable read/write and CAS object implementations. Second, we prove that the bit complexity of every N-process obstruction-free detectable CAS implementation, assuming values from a domain of size at least N, is Ω (N). Finally, we prove that the following holds for obstruction-free detectable implementations of a large class of objects: their recoverable operations must be provided with auxiliary state - state that is not required by the non-recoverable counterpart implementation - whose value must be provided from outside the operation, either by the system or by the caller of the operation. In contrast, this external support is, in general, not required if the recoverable algorithm is not detectable.","PeriodicalId":222366,"journal":{"name":"Proceedings of the 39th Symposium on Principles of Distributed Computing","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124504383","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}