January 2018
Beginner to intermediate
234 pages
7h 8m
Chinese
Content preview from Kafka权威指南
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可靠的数据传递
｜
89
如果跟随者副本不能满足以上任何一点，比如与
Zookeeper
断开连接，或者不再获取新消
息，或者获取消息滞后了
10s
以上，那么它就被认为是不同步的。一个不同步的副本通过
与
Zookeeper
重新建立连接，并从首领那里获取最新消息，可以重新变成同步的。这个过
程在网络出现临时问题并很快得到修复的情况下会很快完成，但如果
broker
发生崩溃就需
要较长的时间。
非同步副本
如果一个或多个副本在同步和非同步状态之间快速切换，说明集群内部出现
了问题，通常是
Java
不恰当的垃圾回收配置导致的。不恰当的垃圾回收配置
会造成几秒钟的停顿，从而让
broker
与
Zookeeper
之间断开连接，最后变成
不同步的，进而发生状态切换。
一个滞后的同步副本会导致生产者和消费者变慢，因为在消息被认为已
提交
之前，客户端
会等待所有同步副本接收消息。而如果一个副本不再同步了，我们就不再关心它是否已经
收到消息。虽然非同步副本同样滞后，但它并不会对性能产生任何影响。但是，更少的同
步副本意味着更低的有效复制系数，在发生宕机时丢失数据的风险更大。
我们将在下一节讲解在实际项目中这将意味着什么。
6.3
broker
配置
broker
有
3
个配置参数会影响
Kafka
消息存储的可靠性。与其他配置参数一样，它们可以
应用在
broker
级别，用于控制所有主题的行为，也可以应用在主题级别，用于控制个别主
题的行为。
在主题级别控制可靠性，意味着
Kafka
集群可以同时拥有可靠的主题和非可靠的主题。例
如，在银行里，管理员可能把整个集群设置为可靠的 ...
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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.