How Flink Watermark is passed between tasks

This article mainly shows you "how to transfer Flink Watermark between tasks". The content is simple and clear. I hope it can help you solve your doubts. Let me lead you to study and learn this article "how to transfer Flink Watermark between tasks".

Watermark is essentially a kind of special data generated from the time stamp in the record in the data stream, which is monotonously increasing. The transfer process in the upstream and downstream is as follows:

For each parallel subtask in the upstream, the watermark in each parallelism is sent as a broadcast to all parallelism downstream. Note that watermark, as a special record, has no key and can only be broadcast to all subtasks downstream.

After receiving the watermark sent by all the subtasks upstream, the downstream selects the smallest watermark as the parallel task and broadcasts it to the downstream.

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