Roles
Paxos describes the actions of the processes by their roles in the protocol: client, acceptor, proposer, learner, and leader. In typical implementations, a single processor may play one or more roles at the same time. This does not affect the correctness of the protocol—it is usual to coalesce roles to improve the latency and/or number of messages in the protocol.
- Client
- The Client issues a request to the distributed system, and waits for a response. For instance, a write request on a file in a distributed file server.
- Acceptor (Voters)
- The Acceptors act as the fault-tolerant "memory" of the protocol. Acceptors are collected into groups called Quorums. Any message sent to an Acceptor must be sent to a Quorum of Acceptors. Any message received from an Acceptor is ignored unless a copy is received from each Acceptor in a Quorum.
- Proposer
- A Proposer advocates a client request, attempting to convince the Acceptors to agree on it, and acting as a coordinator to move the protocol forward when conflicts occur.
- Learner
- Learners act as the replication factor for the protocol. Once a Client request has been agreed on by the Acceptors, the Learner may take action (i.e.: execute the request and send a response to the client). To improve availability of processing, additional Learners can be added.
- Leader
- Paxos requires a distinguished Proposer (called the leader) to make progress. Many processes may believe they are leaders, but the protocol only guarantees progress if one of them is eventually chosen. If two processes believe they are leaders, they may stall the protocol by continuously proposing conflicting updates. However, the safety properties are still preserved on that case.
Read more about this topic: Paxos (computer Science)
Famous quotes containing the word roles:
“Productive collaborations between family and school, therefore, will demand that parents and teachers recognize the critical importance of each other’s participation in the life of the child. This mutuality of knowledge, understanding, and empathy comes not only with a recognition of the child as the central purpose for the collaboration but also with a recognition of the need to maintain roles and relationships with children that are comprehensive, dynamic, and differentiated.”
—Sara Lawrence Lightfoot (20th century)
“There is a striking dichotomy between the behavior of many women in their lives at work and in their lives as mothers. Many of the same women who are battling stereotypes on the job, who are up against unspoken assumptions about the roles of men and women, seem to accept—and in their acceptance seem to reinforce—these roles at home with both their sons and their daughters.”
—Ellen Lewis (20th century)
“A concern with parenting...must direct attention beyond behavior. This is because parenting is not simply a set of behaviors, but participation in an interpersonal, diffuse, affective relationship. Parenting is an eminently psychological role in a way that many other roles and activities are not.”
—Nancy Chodorow (20th century)