January 2018
Beginner to intermediate
234 pages
7h 8m
Chinese
Content preview from Kafka权威指南
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76
｜
第
5
章
找到首选首领
从分区的副本清单里可以很容易找到首选首领（可以使用
kafka.topics.sh
工
具查看副本和分区的详细信息，我们将在第
10
章介绍管理工具）。清单里的
第一个副本一般就是首选首领。不管当前首领是哪一个副本，都不会改变这
个事实，即使使用副本分配工具将副本重新分配给其他
broker
。要记住，如
果你手动进行副本分配，第一个指定的副本就是首选首领，所以要确保首选
首领被传播到其他
broker
上，避免让包含了首领的
broker
负载过重，而其他
broker
却无法为它们分担负载。
5.4
处理请求
broker
的大部分工作是处理客户端、分区副本和控制器发送给分区首领的请求。
Kafka
提
供了一个二进制协议（基于
TCP
），指定了请求消息的格式以及
broker
如何对请求作出
响应——包括成功处理请求或在处理请求过程中遇到错误。客户端发起连接并发送请求，
broker
处理请求并作出响应。
broker
按照请求到达的顺序来处理它们——这种顺序保证让
Kafka
具有了消息队列的特性，同时保证保存的消息也是有序的。
所有的请求消息都包含一个标准消息头：
• Request type
（也就是
API key
）
• Request version
（
broker
可以处理不同版本的客户端请求，并根据客户端版本作出不同
的响应）
• Correlation ID
——一个具有唯一性的数字，用于标识请求消息，同时也会出现在响应消
息和错误日志里（用于诊断问题）
• Client ID
——用于标识发送请求的客户端
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