January 2018
Beginner to intermediate
234 pages
7h 8m
Chinese
Content preview from Kafka权威指南
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跨集群数据镜像
｜
123
另外，我们还要避免循环镜像，相同的事件不能无止境地来回镜像。对于每一个“逻辑
主题”，我们可以在每个数据中心里为它创建一个单独的主题，并确保不要从远程数据中
心复制同名的主题。例如，对于逻辑主题“
users
”，我们在一个数据中心为其创建“
SF.
users
”主题，在另一个数据中心为其创建“
NYC.users
”主题。镜像进程将
SF
的“
SF.
users
”镜像到
NYC
，同时将
NYC
的“
NYC.users
”镜像到
SF
。这样一来，每一个事件只
会被镜像一次，不过在经过镜像之后，每个数据中心同时拥有了
SF.users
和
NYC.users
这
两个主题，也就是说，每个数据中心都拥有相同的用户数据。消费者如果要读取所有的用
户数据，就需要以“
*.users
”的方式订阅主题。我们也可以把这种方式理解为数据中心的
命名空间，比如在这个例子里，
NYC
和
SF
就是命名空间。
在不久的将来，
Kafka
将会增加记录头部信息。头部信息里可以包含源数据中心的信息，
我们可以使用这些信息来避免循环镜像，也可以用它们来单独处理来自不同数据中心的数
据。当然，你也可以通过使用结构化的数据格式（比如
Avro
）来实现这一特性，并用它在
数据里添加标签和头部信息。不过在进行镜像时，需要做一些额外的工作，因为现成的镜
像工具并不支持自定义的头部信息格式。
8.2.4
主备架构
有时候，使用多个集群只是为了达到灾备的目的。你可能在同一个数据中心安装了两个
集群，它们包含相同的数据，平常只使用其中的一个。当提供服务的集群完全不可用时， ...
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