January 2018
Beginner to intermediate
234 pages
7h 8m
Chinese
Content preview from Kafka权威指南
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Kafka
生产者——向
Kafka
写入数据
｜
39
顺序保证
Kafka
可以保证同一个分区里的消息是有序的。也就是说，如果生产者按照
一定的顺序发送消息，
broker
就会按照这个顺序把它们写入分区，消费者也
会按照同样的顺序读取它们。在某些情况下，顺序是非常重要的。例如，往
一个账户存入
100
元再取出来，这个与先取钱再存钱是截然不同的！不过，
有些场景对顺序不是很敏感。
如果把
retries
设为非零整数，同时把
max.in.flight.requests.per.connection
设为比
1
大的数，那么，如果第一个批次消息写入失败，而第二个批次写入
成功，
broker
会重试写入第一个批次。如果此时第一个批次也写入成功，那
么两个批次的顺序就反过来了。
一般来说，如果某些场景要求消息是有序的，那么消息是否写入成功也是
很关键的，所以不建议把
retries
设为
0
。可以把
max.in.flight.requests.
per.connection
设为
1
，这样在生产者尝试发送第一批消息时，就不会有其
他的消息发送给
broker
。不过这样会严重影响生产者的吞吐量，所以只有在
对消息的顺序有严格要求的情况下才能这么做。
3.5
序列化器
我们已经在之前的例子里看到，创建一个生产者对象必须指定序列化器。我们已经知道如
何使用默认的字符串序列化器，
Kafka
还提供了整型和字节数组序列化器，不过它们还不
足以满足大部分场景的需求。到最后，我们需要序列化的记录类型会越来越多。
接下来演示如何开发自己的序列化器，并介绍
Avro
序列化器作为推荐的备选方案。 ...
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