May 2024
Intermediate
278 pages
5h 24m
Chinese
Content preview from 构建可扩展分布式系统：方法与实践
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126
｜
第
7
章
法以便管理副本，并在领导者不可用时选择新的领导者
译注
1
。我将在第
12
章详细讨论
RAFT
算法。
1
仲裁队列必须是持久性的，因此主要适用于数据安全性和可用性优先于性能的用例。在
故障处理方面，它比镜像队列的实现更有优势。考虑到这些原因，镜像队列的实现将在
未来版本中被弃用。
7.3
消息传递模式
这个网站（
https://oreil.ly/DuhYA
）为使用消息传递的应用程序提供了一份全面的设计模
式目录，这些设计模式在企业级系统中有着悠久的使用历史。虽然其中许多都与构建和
修改系统的便捷性以及消息安全性的最佳设计实践有关，但也有一些直接适用于分布式
系统中的可扩展性。接下来的小节我将介绍三种最常用的模式。
7.3.1
竞争消费者
消息传递系统的一个常见需求是尽可能快地消费队列中的消息。竞争消费者模式（
https://
oreil.ly/WHatQ
）是通过运行多个消费者线程或进程并发处理消息来实现的。这使得应用程
序能够根据需要通过水平扩展消费者来扩展消息处理能力。总体设计如图
7-7
所示。
发布者
消息代理
消费者
消费者
消费者
图 7-7：竞争消费者模式
通过竞争消费者模式，可以利用推送或拉取模型动态地在消费者之间分发消息。使
用推送方法时，代理要负责选择将消息传递到哪一个消费者。例如，在
RabbitMQ
和
ActiveMQ
中实现的一种常见方法是简单的循环分发算法。这种方法确保了将消息均衡
地分发给消费者。
使用拉取方法时，消费者只需尽可能快地处理消息。假设有一个多线程消费者，如果一
个消费者在八核节点上运行，另一个在双核节点上运行 ...
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