Results 1  10
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18
Selfstabilizing leader election in networks of finitestate anonymous agents
 In Proc. 10th International Conference on Principles of Distributed Systems, number 4305 in LNCS
, 2006
"... Abstract. This paper considers the selfstabilizing leaderelection problem in a model of interacting anonymous finitestate agents. Leader election is a fundamental problem in distributed systems; many distributed problems are easily solved with the help of a central coordinator. Selfstabilizing al ..."
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Abstract. This paper considers the selfstabilizing leaderelection problem in a model of interacting anonymous finitestate agents. Leader election is a fundamental problem in distributed systems; many distributed problems are easily solved with the help of a central coordinator. Selfstabilizing algorithms do not require initialization in order to operate correctly and can recover from transient faults that obliterate all state information in the system. Anonymous finitestate agents model systems of identical simple computational nodes such as sensor networks and biological computers. Selfstabilizing leader election is easily shown to be impossible in such systems without additional structure. An eventual leader detector Ω? is an oracle that eventually detects the presence or absence of a leader. With the help of Ω?, uniform selfstabilizing leader election algorithms are presented for two natural classes of network graphs: complete graphs and rings. The first algorithm works under either a local or global fairness condition, whereas the second requires global fairness. With only local fairness, uniform selfstabilizing leader election in rings is impossible, even with the help of Ω?.
A robust and lightweight stable leader election service for dynamic systems
 In Proceedings of DSN’08
, 2008
"... We describe the implementation and experimental evaluation of a faulttolerant leader election service for dynamic systems. Intuitively, distributed applications can use this service to elect and maintain an operational leader for any group of processes which may dynamically change. If the leader o ..."
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We describe the implementation and experimental evaluation of a faulttolerant leader election service for dynamic systems. Intuitively, distributed applications can use this service to elect and maintain an operational leader for any group of processes which may dynamically change. If the leader of a group crashes, is temporarily disconnected, or voluntarily leaves the group, the service automatically reelects a new group leader. The current version of the service implements two recent leader election algorithms, and users can select the one that fits their system better. Both algorithms ensure leader stability, a desirable feature that lacks in some other algorithms, but one is more robust in the face of extreme network disruptions, while the other is more scalable. The leader election service is flexible and easy to use. By using a stochastic failure detector [5] and a link quality estimator, it provides some degree of QoS control and it adapts to changing network conditions. Our experimental evaluation indicates that it is also highly robust and inexpensive to run in practice. 1.
How to Choose a Timing Model?
"... When employing a consensus algorithm for state machine replication, should one optimize for the case that all communication links are usually timely, or for fewer timely links? Does optimizing a protocol for better message complexity hamper the time complexity? In this paper, we investigate these ty ..."
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Cited by 9 (1 self)
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When employing a consensus algorithm for state machine replication, should one optimize for the case that all communication links are usually timely, or for fewer timely links? Does optimizing a protocol for better message complexity hamper the time complexity? In this paper, we investigate these types of questions using mathematical analysis as well as experiments over PlanetLab (WAN) and a LAN. We present a new and efficient leaderbased consensus protocol that has O(n) stablestate message complexity (in a system with n processes) and requires only O(n) links to be timely at stable times. We compare this protocol with several previously suggested protocols. Our results show that a protocol that requires fewer timely links can achieve better performance, even if it sends fewer messages.
From an intermittent rotating star to a leader
, 2006
"... Considering an asynchronous system made up of n processes and where up to t of them can crash, finding the weakest assumptions that such a system has to satisfy for a common leader being eventually elected, is one of the holy grail quests of faulttolerant asynchronous computing. This paper is a s ..."
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Cited by 5 (1 self)
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Considering an asynchronous system made up of n processes and where up to t of them can crash, finding the weakest assumptions that such a system has to satisfy for a common leader being eventually elected, is one of the holy grail quests of faulttolerant asynchronous computing. This paper is a step in such a quest. It has two main contributions. First, it proposes an asynchronous system model, in which an eventual leader can be elected, that is weaker and more general than previous models. This model is captured by the notion of intermittent rotating tstar. An xstar is a set of x +1processes: a process p (the center of the star) plus a set of x processes (the points of the star). Intuitively, assuming logical times rn (round numbers), the intermittent rotating tstar assumption means that there are a process p, a subset of the round numbers rn, and associated sets Q(rn) such that each set fpg[Q(rn) is a tstar centered at p, and each process of Q(rn) receives from p a message tagged rn in a timely manner or among the first (n; t) messages tagged rn it ever receives. The star is called trotating because the set Q(rn) is allowed to change with rn. It is called intermittent because the star can disappear during finite periods. This assumption, not only combines, but generalizes several synchrony and timefree assumptions that have been previously proposed to elect an eventual leader (e.g., eventual tsource, eventual tmoving source, message pattern assumption). Each of these assumptions appears as a particular case of the intermittent rotating tstar assumption. The second contribution of the paper is an algorithm that eventually elects a common leader in any system that satisfies the intermittent rotating
Agreement and Consistency Without Knowing the Number of Processes
"... We study in this paper three classical problems of fault tolerance in a system where the set of processes is unknown. These three problems are: the consensus, the implementation of atomics registers and the eventual leader election. For this, we consider different models. In the first one, the com ..."
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We study in this paper three classical problems of fault tolerance in a system where the set of processes is unknown. These three problems are: the consensus, the implementation of atomics registers and the eventual leader election. For this, we consider different models. In the first one, the communication and the processes are asynchronous. In this model, these three problems could not be solved, but we define the weakest failure detectors needed to solve them. We consider then a model where the processes and the communication are synchronous, which permit to realize synchronous rounds. In this case, the processes are created dynamically and may have crash failures. We prove that, if for all rounds at least one process is alive in two consecutive rounds, the consensus and the implementation of registers
With Finite Memory Consensus is Easier Than Reliable Broadcast
, 2008
"... We consider asynchronous distributed systems with message losses and process crashes. We study the impact of finite process memory on the solution to consensus, repeated consensus and reliable broadcast. With finite process memory, we show that in some sense consensus is easier to solve than reliabl ..."
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Cited by 2 (0 self)
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We consider asynchronous distributed systems with message losses and process crashes. We study the impact of finite process memory on the solution to consensus, repeated consensus and reliable broadcast. With finite process memory, we show that in some sense consensus is easier to solve than reliable broadcast, and that reliable broadcast is as difficult to solve as repeated consensus: More precisely, with finite memory, consensus can be solved with failure detector S, and P− (a variant of the perfect failure detector which is stronger than S) is necessary and sufficient to solve reliable broadcast and repeated consensus. Distributed algorithms, failure detectors, reliable broadcast, consensus, repeated consensus.
Minimal system conditions to implement unreliable failure detectors
 University of California
, 2006
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Eventual leader service in unreliable asynchronous systems: Why? how
 In NCA
, 2007
"... Providing processes with an eventual leader service is an important issue when one has to design and implement a middleware layer on top of a failureprone asynchronous distributed system. This invited lecture investigates this problem. It first shows that such a service cannot be built if the under ..."
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Providing processes with an eventual leader service is an important issue when one has to design and implement a middleware layer on top of a failureprone asynchronous distributed system. This invited lecture investigates this problem. It first shows that such a service cannot be built if the underlying system is fully asynchronous. Then, the paper visits several additional behavioral assumptions that have been proposed in the literature to cope with this impossibility and presents corresponding eventual leader election protocols. This lecture can be seen as a guided tour of the eventual leader service problem, whose aim is to benefit researchers and system engineers working in distributed middleware built on top of asynchronous networks.
From an Intermittent Rotating Star to a Leader
, 2006
"... Abstract. Considering an asynchronous system made up of n processes and where up to t of them can crash, finding the weakest assumptions that such a system has to satisfy for a common leader to be eventually elected is one of the holy grail quests of faulttolerant asynchronous computing. This paper ..."
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Cited by 2 (1 self)
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Abstract. Considering an asynchronous system made up of n processes and where up to t of them can crash, finding the weakest assumptions that such a system has to satisfy for a common leader to be eventually elected is one of the holy grail quests of faulttolerant asynchronous computing. This paper is a step in such a quest. It has two main contributions. First, it proposes an asynchronous system model, in which an eventual leader can be elected, that is weaker and more general than previous models. This model is captured by the notion of intermittent rotating tstar. An xstar is a set of x + 1 processes: a process p (the center of the star) plus a set of x processes (the points of the star). Intuitively, assuming logical times rn (round numbers), the intermittent rotating tstar assumption means that there are a process p, a subset of the round numbers rn, and associated sets Q(rn) such that each set {p}∪Q(rn) is a tstar centered at p, and each process of Q(rn) receives from p a message tagged rn in a timely manner or among the first (n − t) messages tagged rn it ever receives. The star is called trotating because the set Q(rn) is allowed to change with rn. It is called intermittent
Specifying and Implementing an Eventual Leader Service for Dynamic Systems
, 2010
"... Abstract: The election of an eventual leader in an asynchronous system prone to process crashes is an important problem of faulttolerant distributed computing. This problem is known as the implementation of the failure detector Ω. Nearly all papers that propose algorithms implementing such an eventu ..."
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Abstract: The election of an eventual leader in an asynchronous system prone to process crashes is an important problem of faulttolerant distributed computing. This problem is known as the implementation of the failure detector Ω. Nearly all papers that propose algorithms implementing such an eventual leader service consider a static system. In contrast this paper considers a dynamic system, i.e., a system in which processes can enter and leave. The paper has three contributions. It first proposes a specification of Ω suited to dynamic systems. Then, it presents and proves correct an algorithm implementing this specification. Finally, the paper discusses the notion of an eventual leader suited to dynamic systems. It introduces an additional property related to system stability. The design of an algorithm satisfying this last property remains an open challenging problem.