Managed Agreement: Generalizing two fundamental distributed agreement problems

Consensus and Non-Blocking Atomic Commit (NBAC) are two fundamental distributed problems. The specifications of both problems may lead one to think that they are very similar. However, a black-box solution to any of them is not sufficient to solve the other. This paper presents a family of agreement problems called Managed Agreement, which is parameterized by the number of aristocrat nodes in the system; NBAC is a special case of this family when all nodes are aristocrats while Consensus is a special case of this family when there are no aristocrats. The paper also presents a parameterized family of failure detectors F(A) such that F(A) is the weakest failure detector class that enables solving Managed Agreement with a set A of aristocrats in an asynchronous environment. Key-words: consensus, non-blocking atomic commit, quitable consensus, managed agreement, failure detectors