55 lines
2.4 KiB
Markdown
55 lines
2.4 KiB
Markdown
# Paxos
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- **期号**: SRE Weekly Issue #305（2022-01-16）
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- **作者**: Martin Fowler
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- **链接**: https://martinfowler.com/articles/patterns-of-distributed-systems/paxos.html
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## 简介
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This is an approachable explanation of the Paxos algorithm with examples, diagrams, and code.
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## 正文
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# Paxos
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Use two consensus building phases to reach safe consensus even when nodes disconnect
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## Problem
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When multiple nodes share state, they often need to agree between
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themselves on a particular value.
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With [Leader and Followers](https://martinfowler.com/leader-follower.html), the leader decides and passes its value to the
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followers. But if there is no leader, then the nodes need to determine a
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value themselves. (Even with a leader-follower, they may need to do this to
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elect a leader.)
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A leader can ensure that replicas safely acquire an update by using
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[Two-Phase Commit](https://martinfowler.com/two-phase-commit.html), but without a leader we can have competing nodes
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attempt to gather a [Majority Quorum](https://martinfowler.com/majority-quorum.html). This process is further
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complicated because any node may fail or disconnect. A node may achieve
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majority quorum on a value, but disconnect before it is able to communicate this
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value to the entire cluster.
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## Solution
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The Paxos algorithm was developed by Leslie Lamport,
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published in his 1998 paper [“The
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Part-Time Parliament”](http://lamport.azurewebsites.net/pubs/lamport-paxos.pdf). Paxos works in three phases to make sure
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multiple nodes agree on the same value in spite of partial network or
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node failures. The first two phases act to build consensus around a
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value and the last phase then communicates that consensus to the remaining
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replicas.
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- Prepare phase: Establish the latest [Generation Clock](https://martinfowler.com/generation-clock.html) and gather any already accepted values.
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- Accept phase: Propose a value for this generation for replicas to accept.
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- Commit phase: Let all the replicas know that a value has been chosen.
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for more details go to [Chapter 11](https://learning.oreilly.com/library/view/patterns-of-distributed/9780138222246/ch11.xhtml) of the online ebook at oreilly.com
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This pattern is part of [Patterns of Distributed Systems](https://martinfowler.com/)
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23 November 2023
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