November 2022
Beginner to intermediate
346 pages
11h
Chinese
Content preview from Kafka权威指南（第2版）
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62
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第
4
章
的，只要消费者能够以正常的时间间隔发送心跳，它就会被认为还“活着”。
如果消费者在足够长的一段时间内没有发送心跳，那么它的会话就将超时，群组协调器会
认为它已经“死亡”，进而触发再均衡。如果一个消费者发生崩溃并停止读取消息，那么
群组协调器就会在几秒内收不到心跳，它会认为消费者已经“死亡”，进而触发再均衡。
在这几秒时间里，“死掉”的消费者不会读取分区里的消息。在关闭消费者后，协调器会
立即触发一次再均衡，尽量降低处理延迟。本章的后续部分将介绍一些用于控制心跳发送
频率、会话过期时间和调节消费者行为的配置参数。
分配分区是怎样的一个过程
？
当一个消费者想要加入消费者群组时，它会向群组协调器发送
JoinGroup
请求。第一个加入群组的消费者将成为群组
首领
。首领从群组协调器那里
获取群组的成员列表（列表中包含了所有最近发送过心跳的消费者，它
们被认为还“活着”），并负责为每一个消费者分配分区。它使用实现了
PartitionAssignor
接口的类来决定哪些分区应该被分配给哪个消费者。
Kafka
内置了一些分区分配策略
，后文将深入介绍它们。分区分配完毕之后，
首领会把分区分配信息发送给群组协调器，群组协调器再把这些信息发送给
所有的消费者。每个消费者只能看到自己的分配信息，只有首领会持有所有
消费者及其分区所有权的信息。每次再均衡都会经历这个过程。
4.1.3
群组固定成员
在默认情况下，消费者的群组成员身份标识是临时的。当一个消费者离开群组时，分配给
它的分区所有权将被撤销；当该消费者重新加入时，将通过再均衡协议为其分配一个新的 ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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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.