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A Topological Treatment of EarlyDeciding SetAgreement
, 2008
"... The ksetagreement problem consists for a set of n processes to agree on less than k among n possibly different values, each initially known to only one process. The problem is at the heart of distributed computing and generalizes the celebrated consensus problem. This paper considers the ksetagr ..."
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The ksetagreement problem consists for a set of n processes to agree on less than k among n possibly different values, each initially known to only one process. The problem is at the heart of distributed computing and generalizes the celebrated consensus problem. This paper considers the ksetagreement problem in a synchronous message passing distributed system where up to t processes can fail by crashing. We determine the number of communication rounds needed for all correct processes to reach a decision in a given run, as a function of the degree of coordination k and the number of processes that actually fail in the run, f ≤ t. We prove that, for any integer 1 ≤ k < n, for any setagreement protocol, for any integer 0 ≤ f ≤ t, not all correct processes can decide within ⌊f/k ⌋ + 1 rounds, in any run with at most f process crashes. More specifically, we prove a lower bound of min(⌊f/k ⌋ + 2, ⌊t/k ⌋ + 1) rounds for earlydeciding setagreement. This bound is tight because there is a setagreement protocol that matches it, and the bound generalizes both the min(f + 2, t + 1) bound previously obtained for earlydeciding consensus and the t + 1 bound previously obtained for the worstcase complexity of setagreement.
présentée par Hung TRANTHE
"... Comme une évidence pour débuter ces remerciements, je voudrais remercier chaudement Carole Delporte et Hugues Fauconnier, directeurs de ma thèse. Je vous remercie beaucoup ..."
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Comme une évidence pour débuter ces remerciements, je voudrais remercier chaudement Carole Delporte et Hugues Fauconnier, directeurs de ma thèse. Je vous remercie beaucoup
The PerfectlySynchronized Roundbased Model of Distributed Computing
"... The perfectlysynchronized roundbased model provides the powerful abstraction of crashstop failures with atomic and synchronous message delivery. This abstraction makes distributed programming very easy. We describe a technique to automatically transform protocols devised in the perfectlysynchron ..."
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The perfectlysynchronized roundbased model provides the powerful abstraction of crashstop failures with atomic and synchronous message delivery. This abstraction makes distributed programming very easy. We describe a technique to automatically transform protocols devised in the perfectlysynchronized roundbased model into protocols for the crash, send omission, general omission or Byzantine models. Our transformation is achieved using a round shifting technique with a constant time complexity overhead. The overhead depends on the target model: crashes, send omissions, general omissions or Byzantine failures. Rather surprisingly, we show that no other automatic nonuniform transformation from a weaker model, say from the traditional crashstop model (with no atomic message delivery), onto an even stronger model than the generalomission one, say the sendomission model, can provide a better time complexity performance in a failurefree execution.