Unreliable Failure Detectors with Limited Scope Accuracy and an Application to Consensus

Abstract

Let the scope of the accuracy property ofan unreliable failure detector be the minimum number (k) ofpro cesses that may not erroneously suspect a correct process to have crashed. Classical failure detectors implicitly consider a scope equal to n (the total number ofp rocesses). This paper investigates accuracy properties with limited scope, thereby giving rise to the S _k and ◊S _k classes off ailure detectors. A reduction protocol transforming any failure detector belonging to S _k (resp. ◊S _k ) into a failure detector (without limited scope) of the class S (resp. ◊S) is given. This reduction protocol requires f < k, where f is the maximum number ofp rocess crashes. (This leaves open the problem to prove/disprove that this condition is necessary.) Then, the paper studies the consensus problem in asynchronous distributed message-passing systems equipped with a failure detector of the class ◊S _k . It presents a simple consensus protocol that is explicitly based on ◊S _k . This protocol requires f < min(k, n/2).