January 2018
Beginner to intermediate
234 pages
7h 8m
Chinese
Content preview from Kafka权威指南
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78
｜
第
5
章
5.4.1
生产请求
我们在第
3
章讨论如何配置生产者的时候，提到过 acks 这个配置参数——该参数指定了需
要多少个
broker
确认才可以认为一个消息写入是成功的。不同的配置对“写入成功”的界
定是不一样的，如果 acks=1，那么只要首领收到消息就认为写入成功；如果 acks=all，那
么需要所有同步副本收到消息才算写入成功；如果 acks=0，那么生产者在把消息发出去之
后，完全不需要等待
broker
的响应。
包含首领副本的
broker
在收到生产请求时，会对请求做一些验证。
•
发送数据的用户是否有主题写入权限？
•
请求里包含的 acks 值是否有效（只允许出现 0、1 或 all）？
•
如果 acks=all，是否有足够多的同步副本保证消息已经被安全写入？（我们可以对
broker
进行配置，如果同步副本的数量不足，
broker
可以拒绝处理新消息。在第
6
章介
绍
Kafka
持久性和可靠性保证时，我们会讨论更多这方面的细节。）
之后，消息被写入本地磁盘。在
Linux
系统上，消息会被写到文件系统缓存里，并不保证
它们何时会被刷新到磁盘上。
Kafka
不会一直等待数据被写到磁盘上——它依赖复制功能
来保证消息的持久性。
在消息被写入分区的首领之后，
broker
开始检查 acks 配置参数——如果 acks 被设为 0 或 1，
那么
broker
立即返回响应；如果 acks 被设为 all，那么请求会被保存在一个叫作
炼狱
的缓冲
区里，直到首领发现所有跟随者副本都复制了消息，响应才会被返回给客户端。 ...
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