January 2018
Beginner to intermediate
234 pages
7h 8m
Chinese
Content preview from Kafka权威指南
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Kafka
消费者——从
Kafka
读取数据
｜
55
线程安全
在同一个群组里，我们无法让一个线程运行多个消费者，也无法让多个线
程安全地共享一个消费者。按照规则，一个消费者使用一个线程。如果
要在同一个消费者群组里运行多个消费者，需要让每个消费者运行在自己
的线程里。最好是把消费者的逻辑封装在自己的对象里，然后使用
Java
的
ExecutorService
启动多个线程，使每个消费者运行在自己的线程上。
Confluent
的博客（
https://www.confluent.io/blog/
）上有一个教程介绍如何处
理这种情况。
4.5
消费者的配置
到目前为止，我们学习了如何使用消费者
API
，不过只介绍了几个配置属性——
bootstrap.
servers
、
group.id
、
key.deserializer
和
value.deserializer
。
Kafka
的文档列出了所有与消费者相
关的配置说明。大部分参数都有合理的默认值，一般不需要修改它们，不过有一些参数与消费
者的性能和可用性有很大关系。接下来介绍这些重要的属性。
1. fetch.min.bytes
该属性指定了消费者从服务器获取记录的最小字节数。
broker
在收到消费者的数据请求时，
如果可用的数据量小于 fetch.min.bytes 指定的大小，那么它会等到有足够的可用数据时
才把它返回给消费者。这样可以降低消费者和
broker
的工作负载，因为它们在主题不是很
活跃的时候（或者一天里的低谷时段）就不需要来来回回地处理消息。如果没有很多可用
数据，但消费者的 ...
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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.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
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.