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Kafka Topic Reuse

Martin Kleppmann walks through the trade-offs of reusing Apache Kafka topics for different event types:

The common wisdom (according to several conversations I’ve had, and according to a mailing list thread) seems to be: put all events of the same type in the same topic, and use different topics for different event types. That line of thinking is reminiscent of relational databases, where a table is a collection of records with the same type (i.e. the same set of columns), so we have an analogy between a relational table and a Kafka topic.

The Confluent Avro Schema Registry has traditionally reinforced this pattern, because it encourages you to use the same Avro schema for all messages in a topic. That schema can be evolved while maintaining compatibility (e.g. by adding optional fields), but ultimately all messages have been expected to conform to a certain record type. We’ll revisit this later in the post, after we’ve covered some more background.

For some types of streaming data, such as logged activity events, it makes sense to require that all messages in the same topic conform to the same schema. However, some people are using Kafka for more database-like purposes, such as event sourcing, or exchanging data between microservices. In this context, I believe it’s less important to define a topic as a grouping of messages with the same schema. Much more important is the fact that Kafka maintains ordering of messages within a topic-partition.

Read the whole thing.