Getting started with Paxos

Paxos  The algorithm is Leslie - Lambert On 1990 A consistency algorithm based on message passing was proposed in .

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Basic-Paxos

Role Introduction

• Client Request originator , External role of the system
• Proposer receive Client request , Propose to the cluster . Play the role of conflict regulation
• Acceptor Propose votes and recipients , Only in the trip quorum （Quorum） when , The proposal will eventually be accepted .（ Arbitration system ）
• Learner Propose to the recipient , Backup , It has no impact on cluster consistency （ Don't vote ）

Steps and stages

• 1、Prepare

Proposer Put forward a proposal , The number is N, this N Greater than this Proposer Previous proposal number . request acceptor Of quorum receive

• 2、Promise

If N More than that acceptor Any proposal number previously received is accepted , Otherwise, refuse

• 3、Accept

If we reach the majority ,proposer Will be issued acceptor request , This request contains the proposal number N, And the content

• 4、Accepted

If so acceptor No greater than... Was received during this period N Proposal for , Then accept the content of this proposal , Otherwise ignore

flow chart

1. Some nodes fail , We can still reach a consensus
2. Proposer Failure ,

Potential problems – Live lock

Difficulty in realization , Low efficiency （2 round RPC）, The following two algorithms are proposed

• Multi Paxos
• Fast Paxos