The Heard-Of Model: Computing in Distributed Systems with Benign Failures

<html> <body> Problems in fault-tolerant distributed computing have been studied in a variety of models. These models are structured around two central ideas: <OL><LI>Degree of synchrony and failure model are two <em>independent</em> parameters that determine a particular type of system. <LI> The notion of <em>faulty</em> component is helpful and even necessary for the analysis of distributed computations when failures occur. </OL><p>In this work, we question these two basic principles of fault-tolerant distributed computing, and show that it is both possible and worthy to renounce them in the context of benign failures: we present a computational model, suitable for systems with benign failures, which is based only on the notion of <em>transmission failure</em>. </p><p> In this model, computations evolve in rounds, and messages missed at a round are lost. Only information transmission is represented: for each round r and each process p, our model provides the set of processes that p ``hears of'' at round r (<em>heard-of set</em>) namely the processes from which p receives some message at round r. The features of a specific system are thus captured as a whole, just by a predicate over the collection of heard-of sets. We show that our model handles benign failures, be they static or dynamic, permanent or transient, in a unified framework. </p><p> Using this new approach, we are able to give shorter and simpler proofs of important results (non-solvability, lower bounds). In particular, we prove that in general, Consensus cannot be solved without an implicit and permanent consensus on heard-of sets. We also examine Consensus algorithms in our model. In light of this specific agreement problem, we show how our approach allows us to devise new interesting solutions. </p> </body> </html>

Replaces TR-2006: The Heard-Of Model: Unifying all Benign Failures.

 Record created 2007-07-04, last modified 2019-01-17

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