有没有办法在具有单个使用者的 kafka 主题的分区之间维护消息排序？

Question

We are developing a kafka based streaming system in which the producer would produce to multiple partitions within its topic and a single consumer would consume from the topic. I know that kafka maintains message order within partitions, but can we maintain a global message order between partitions within a topic?

Answer 1

Short answer: no, Kafka does not provide any ordering guarantees between partitions.

Long answer: I don't quite understand your problem. If you are saying you have only one consumer consuming your topic, why would you have more than 1 partition in that topic and reinvent the wheel trying to maintain order between partitions? If you want to leave some space for future growth, eg adding another consumer to consume a part of partitions, then you'll have to rethink your "global message order" idea.

Do you really need ALL messages to be processed in order? Or maybe you could partition by client/application/whatever and maintain order per partition? In most cases you don't really need that global message order, but just have to partition your data properly.

Maintaining order between multiple consumers is a really tough problem to solve, and even if solved correctly you'll just neglect all Kafka benefits.

Answer 2

You can't benifit from kafka if you want the global ordering in more than one partition. Kafka only supports message ordering in only one partition. In our company, we need only the same catergory messages are sent to the same partition, which can easily partition using partitionId.

Answer 3

The purpose of partitions in Kafka is to create a partial order of messages in a broader topic, where the messages follow a strict total order in any given partition. So the answer is 'no', it would defeat the purpose of partitions if any notion of cross-partition order were to be introduced.

I would suggest instead focusing on how messages (records, in Kafka parlance) are keyed, which effectively determines how they are mapped to a partition. Which partition specifically doesn't matter, as long as the mapping is deterministic and repeatable — all you should care about is that identically keyed records will always appear on the same partition and, hence, will not be assigned to multiple consumers at the same time (within the same consumer group).

If you are publishing updates to persisted entities, the primary key of the entity is typically a good starting point for a Kafka record key. If there needs to be some order of updates across a connected graph of entities, then taking the ID root of the graph and making it the key will likely satisfy your ordering needs.