Classic Paxos Sample Clauses

Classic Paxos. ‌ The rounds of Paxos and Fast Paxos are identified by round numbers (sometimes also called a ballot numbers [Lamport, 1998]) which are totally ordered by a relation < and in an infinite number. Although there is a total order among round numbers, the execution of rounds need not follow this order, and actions referring to different rounds may even interleave. This is in opposition to our WAB-based consensus protocols, in which a round i is always followed by round i + 1 (although delayed agents may skip some rounds). For now, we assume that round numbers correspond to the set of natural numbers. In Section 3.4.5 we discuss another type of round numbers and their interesting properties in Section 3.4.5. We say that a value is chosen in a round r if a quorum of acceptors has accepted the value in round r . Because the protocol assumes that Quorum Requirement (Assumption 1, on page 13) is satisfied, it is ensured that only a single value can be chosen in any round. In Classic Paxos, a round is divided into two phases: the first phase serves to identify previously chosen values and the second phase tries to get some value chosen in the current round. Each phase involves two actions: Phase1a, Phase1b, Phase2a, and Phase2b. Actions Phase1a and Phase2a initiate each phase, while the actions Phase1b and Phase2b may be seen as replies to the previous actions. To orchestrate round executions, Xxxxx assumes a set of coordinator processes, besides proposers, acceptors, and learners. Every round has a single coordinator, responsible for starting each phase of the round, by executing actions Phase1a and Phase1b.1 Two other actions complete the algorithm. The first, Propose, is executed by proposers to propose a value. The second, Learn, is executed by learners to learn the decision of a consensus instance.