January 2018
Beginner to intermediate
234 pages
7h 8m
Chinese
Content preview from Kafka权威指南
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6
｜
第
1
章
消费者
读取消息。在其他发布与订阅系统中，消费者可能被称为
订阅者
或
读者
。消费者订
阅一个或多个主题，并按照消息生成的顺序读取它们。消费者通过检查消息的偏移量来区
分已经读取过的消息。
偏移量
是另一种元数据，它是一个不断递增的整数值，在创建消息
时，
Kafka
会把它添加到消息里。在给定的分区里，每个消息的偏移量都是唯一的。消费
者把每个分区最后读取的消息偏移量保存在
Zookeeper
或
Kafka
上，如果消费者关闭或重
启，它的读取状态不会丢失。
消费者是
消费者群组
的一部分，也就是说，会有一个或多个消费者共同读取一个主题。群
组保证每个分区只能被一个消费者使用。图
1-6
所示的群组中，有
3
个消费者同时读取一
个主题。其中的两个消费者各自读取一个分区，另外一个消费者读取其他两个分区。消费
者与分区之间的映射通常被称为消费者对分区的
所有权关系
。
通过这种方式，消费者可以消费包含大量消息的主题。而且，如果一个消费者失效，群组
里的其他消费者可以接管失效消费者的工作。第
4
章将详细介绍消费者和消费者群组。
分区0
分区1
分区2
分区3
主题“topicName”
消费者0
消费者1
消费者2
消费者
群组
图 1-6：消费者群组从主题读取消息
1.2.5
broker
和集群
一个独立的
Kafka
服务器被称为
broker
。
broker
接收来自生产者的消息，为消息设置偏移
量，并提交消息到磁盘保存。
broker
为消费者提供服务，对读取分区的请求作出响应，返
回已经提交到磁盘上的消息。根据特定的硬件及其性能特征，单个
broker
可以轻松处理数 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.