{"title":"Session details: Session 1A: Persistent Memory","authors":"I. Keidar","doi":"10.1145/3258695","DOIUrl":"https://doi.org/10.1145/3258695","url":null,"abstract":"","PeriodicalId":198284,"journal":{"name":"Proceedings of the 2018 ACM Symposium on Principles of Distributed Computing","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121933536","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}
We consider the exploration problem in undirected graphs without node labels, which requires that a mobile agent initially placed at an arbitrary node visits all nodes and terminates. We assume that both of the agent and nodes are equipped with little memory, and the algorithm cannot use any initial knowledge on the topology of the graph. In this paper, we propose a new deterministic polynomial-time exploration (more precisely, depth-first search) algorithm which can be implemented using only O(1)-bit memory of the agent and O(1)-bit storage for each node. To the best of our knowledge, this is the first polynomial-time exploration algorithm achieving both sublogarithmic memory and sublogarithmic storage. The technical ingredient of our algorithm consists of the idea from the recent progress on small-space DFS algorithms by Asano et al. [ISAAC2014] and Elmasry et al. [STACS2015], and a new distributed backtrack algorithm for DFS paths. The algorithm also includes a new compact (i.e., using O(1)-bit storage) s-t path maintenance mechanism, which may be of independent interest.
{"title":"Brief Announcement: Graph Exploration Using Constant-Size Memory and Storage","authors":"Naoki Kitamura, Kazuki Kakizawa, Yuya Kawabata, Taisuke Izumi","doi":"10.1145/3212734.3212780","DOIUrl":"https://doi.org/10.1145/3212734.3212780","url":null,"abstract":"We consider the exploration problem in undirected graphs without node labels, which requires that a mobile agent initially placed at an arbitrary node visits all nodes and terminates. We assume that both of the agent and nodes are equipped with little memory, and the algorithm cannot use any initial knowledge on the topology of the graph. In this paper, we propose a new deterministic polynomial-time exploration (more precisely, depth-first search) algorithm which can be implemented using only O(1)-bit memory of the agent and O(1)-bit storage for each node. To the best of our knowledge, this is the first polynomial-time exploration algorithm achieving both sublogarithmic memory and sublogarithmic storage. The technical ingredient of our algorithm consists of the idea from the recent progress on small-space DFS algorithms by Asano et al. [ISAAC2014] and Elmasry et al. [STACS2015], and a new distributed backtrack algorithm for DFS paths. The algorithm also includes a new compact (i.e., using O(1)-bit storage) s-t path maintenance mechanism, which may be of independent interest.","PeriodicalId":198284,"journal":{"name":"Proceedings of the 2018 ACM Symposium on Principles of Distributed Computing","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125947519","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":"Session details: Session 1C: Wireless Networks","authors":"J. Burman","doi":"10.1145/3258697","DOIUrl":"https://doi.org/10.1145/3258697","url":null,"abstract":"","PeriodicalId":198284,"journal":{"name":"Proceedings of the 2018 ACM Symposium on Principles of Distributed Computing","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129428059","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":"Session details: Session 2C: Security, Blockchains, and Replication","authors":"G. Chockler","doi":"10.1145/3258701","DOIUrl":"https://doi.org/10.1145/3258701","url":null,"abstract":"","PeriodicalId":198284,"journal":{"name":"Proceedings of the 2018 ACM Symposium on Principles of Distributed Computing","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124647414","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":"Session details: Session 1D: Graph Algorithms","authors":"Peter Robinson","doi":"10.1145/3258698","DOIUrl":"https://doi.org/10.1145/3258698","url":null,"abstract":"","PeriodicalId":198284,"journal":{"name":"Proceedings of the 2018 ACM Symposium on Principles of Distributed Computing","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126551261","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}
Dan Alistarh, Trevor Brown, Justin Kopinsky, Giorgi Nadiradze
There has been significant progress in understanding the parallelism inherent to iterative sequential algorithms: for many classic algorithms, the depth of the dependence structure is now well understood, and scheduling techniques have been developed to exploit this shallow dependence structure for efficient parallel implementations. A related, applied research strand has studied methods by which certain iterative task-based algorithms can be efficiently parallelized via relaxed concurrent priority schedulers. These allow for high concurrency when inserting and removing tasks, at the cost of executing superfluous work due to the relaxed semantics of the scheduler. In this work, we take a step towards unifying these two research directions, by showing that there exists a family of relaxed priority schedulers that can efficiently and deterministically execute classic iterative algorithms such as greedy maximal independent set (MIS) and matching. Our primary result shows that, given a randomized scheduler with an expected relaxation factor of k in terms of the maximum allowed priority inversions on a task, and any graph on n vertices, the scheduler is able to execute greedy MIS with only an additive factor of poly(k) expected additional iterations compared to an exact (but not scalable) scheduler. This counter-intuitive result demonstrates that the overhead of relaxation when computing MIS is not dependent on the input size or structure of the input graph. Experimental results show that this overhead can be clearly offset by the gain in performance due to the highly scalable scheduler. In sum, we present an efficient method to deterministically parallelize iterative sequential algorithms, with provable runtime guarantees in terms of the number of executed tasks to completion.
{"title":"Relaxed Schedulers Can Efficiently Parallelize Iterative Algorithms","authors":"Dan Alistarh, Trevor Brown, Justin Kopinsky, Giorgi Nadiradze","doi":"10.1145/3212734.3212756","DOIUrl":"https://doi.org/10.1145/3212734.3212756","url":null,"abstract":"There has been significant progress in understanding the parallelism inherent to iterative sequential algorithms: for many classic algorithms, the depth of the dependence structure is now well understood, and scheduling techniques have been developed to exploit this shallow dependence structure for efficient parallel implementations. A related, applied research strand has studied methods by which certain iterative task-based algorithms can be efficiently parallelized via relaxed concurrent priority schedulers. These allow for high concurrency when inserting and removing tasks, at the cost of executing superfluous work due to the relaxed semantics of the scheduler. In this work, we take a step towards unifying these two research directions, by showing that there exists a family of relaxed priority schedulers that can efficiently and deterministically execute classic iterative algorithms such as greedy maximal independent set (MIS) and matching. Our primary result shows that, given a randomized scheduler with an expected relaxation factor of k in terms of the maximum allowed priority inversions on a task, and any graph on n vertices, the scheduler is able to execute greedy MIS with only an additive factor of poly(k) expected additional iterations compared to an exact (but not scalable) scheduler. This counter-intuitive result demonstrates that the overhead of relaxation when computing MIS is not dependent on the input size or structure of the input graph. Experimental results show that this overhead can be clearly offset by the gain in performance due to the highly scalable scheduler. In sum, we present an efficient method to deterministically parallelize iterative sequential algorithms, with provable runtime guarantees in terms of the number of executed tasks to completion.","PeriodicalId":198284,"journal":{"name":"Proceedings of the 2018 ACM Symposium on Principles of Distributed Computing","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127983905","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}
A standard design pattern found in many concurrent data structures, such as hash tables or ordered containers, is an alternation of parallelizable sections that incur no data conflicts and critical sections that must run sequentially and are protected with locks. A lock can be viewed as a queue that arbitrates the order in which the critical sections are executed, and a natural question is whether we can use stochastic analysis to predict the resulting throughput. As a preliminary evidence to the affirmative, we describe a simple model that can be used to predict the throughput of coarse-grained lock-based algorithms. We show that our model works well for CLH lock, and we expect it to work for other popular lock designs such as TTAS, MCS, etc.
{"title":"Brief Announcement: Performance Prediction for Coarse-Grained Locking","authors":"V. Aksenov, Dan Alistarh, P. Kuznetsov","doi":"10.1145/3212734.3212785","DOIUrl":"https://doi.org/10.1145/3212734.3212785","url":null,"abstract":"A standard design pattern found in many concurrent data structures, such as hash tables or ordered containers, is an alternation of parallelizable sections that incur no data conflicts and critical sections that must run sequentially and are protected with locks. A lock can be viewed as a queue that arbitrates the order in which the critical sections are executed, and a natural question is whether we can use stochastic analysis to predict the resulting throughput. As a preliminary evidence to the affirmative, we describe a simple model that can be used to predict the throughput of coarse-grained lock-based algorithms. We show that our model works well for CLH lock, and we expect it to work for other popular lock designs such as TTAS, MCS, etc.","PeriodicalId":198284,"journal":{"name":"Proceedings of the 2018 ACM Symposium on Principles of Distributed Computing","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128167705","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":"Session details: Session 3D: Graphs and Population","authors":"Michael Elkin","doi":"10.1145/3258705","DOIUrl":"https://doi.org/10.1145/3258705","url":null,"abstract":"","PeriodicalId":198284,"journal":{"name":"Proceedings of the 2018 ACM Symposium on Principles of Distributed Computing","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126869249","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}
The tutorial provides an overview of the principles and "pearls'' of constructing, maintaining and optimizing network topologies, such as peer-to-peer overlays or datacenter interconnects. The tutorial consists of two parts: Self-stabilization: In the first part, we start simple by discussing basic mechanisms to reconfigure networks while maintaining connectivity. You will then learn how to design and analyze self-stabilizing algorithms for line topologies as well as more sophisticated networks such as hypercubes. A self-stabilizing algorithm guarantees that the network will automatically reconfigure to a "good topology" from an arbitrary initial state. Self-optimization: After we have learned how to design self-stabilizing networks, we will consider algorithms to design self-adjusting resp. "self-optimizing" networks: networks which not only "repair" themselves but also optimize themselves towards the demand. The study of such self-adjusting networks is motivated by emerging technologies in the context of datacenters and wide-area networks, allowing to reconfigure networks at runtime.
{"title":"From Self-Stabilization to Self-Optimization: Principles of Distributed Network Design","authors":"S. Schmid","doi":"10.1145/3212734.3212801","DOIUrl":"https://doi.org/10.1145/3212734.3212801","url":null,"abstract":"The tutorial provides an overview of the principles and \"pearls'' of constructing, maintaining and optimizing network topologies, such as peer-to-peer overlays or datacenter interconnects. The tutorial consists of two parts: Self-stabilization: In the first part, we start simple by discussing basic mechanisms to reconfigure networks while maintaining connectivity. You will then learn how to design and analyze self-stabilizing algorithms for line topologies as well as more sophisticated networks such as hypercubes. A self-stabilizing algorithm guarantees that the network will automatically reconfigure to a \"good topology\" from an arbitrary initial state. Self-optimization: After we have learned how to design self-stabilizing networks, we will consider algorithms to design self-adjusting resp. \"self-optimizing\" networks: networks which not only \"repair\" themselves but also optimize themselves towards the demand. The study of such self-adjusting networks is motivated by emerging technologies in the context of datacenters and wide-area networks, allowing to reconfigure networks at runtime.","PeriodicalId":198284,"journal":{"name":"Proceedings of the 2018 ACM Symposium on Principles of Distributed Computing","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131459447","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}
Geo-distributed services that are executed across multiple sites at a global scale are increasingly prevalent, and are at the core of the control plane tasked with managing the Virtual Network Functions (VNFs) of next-generation network infrastructure. A key building block of any replicated service of this type is logically shared state, an abstraction that is often implemented by having multiple copies of each data element and using one of any number of distributed protocols to enforce consistency with guarantees ranging from eventual to causal to sequential consistency. These solutions fail to meet the real needs of geo-distributed services found in a VNF control plane (and elsewhere), which are to provide guarantees strong enough to be useful, yet still efficiently implementable in a global network with larger latencies and a wider range of failure modes. Here, we propose a new solution to state consistency based on extending entry consistency, a paradigm originally developed for failure-free multi-processor systems, for use in geo-distributed services with failures. We outline the challenges associated with state consistency in such services, and describe a data-store called MUSIC (MUlti-SIte entry Consistency) that combines an eventually consistent key-value store with locking primitives to implement entry-consistent semantics.
{"title":"Brief Announcement: MUSIC: Multi-Site Entry Consistencyfor Geo-Distributed Services","authors":"Bharath Balasubramanian, R. Schlichting, P. Zave","doi":"10.1145/3212734.3212782","DOIUrl":"https://doi.org/10.1145/3212734.3212782","url":null,"abstract":"Geo-distributed services that are executed across multiple sites at a global scale are increasingly prevalent, and are at the core of the control plane tasked with managing the Virtual Network Functions (VNFs) of next-generation network infrastructure. A key building block of any replicated service of this type is logically shared state, an abstraction that is often implemented by having multiple copies of each data element and using one of any number of distributed protocols to enforce consistency with guarantees ranging from eventual to causal to sequential consistency. These solutions fail to meet the real needs of geo-distributed services found in a VNF control plane (and elsewhere), which are to provide guarantees strong enough to be useful, yet still efficiently implementable in a global network with larger latencies and a wider range of failure modes. Here, we propose a new solution to state consistency based on extending entry consistency, a paradigm originally developed for failure-free multi-processor systems, for use in geo-distributed services with failures. We outline the challenges associated with state consistency in such services, and describe a data-store called MUSIC (MUlti-SIte entry Consistency) that combines an eventually consistent key-value store with locking primitives to implement entry-consistent semantics.","PeriodicalId":198284,"journal":{"name":"Proceedings of the 2018 ACM Symposium on Principles of Distributed Computing","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2018-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133960788","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}
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