Re: Watermarks in Event Time windowing

Posted by vino yang on
URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/Watermarks-in-Event-Time-windowing-tp23061p23064.html

Hi Taher,

For some questions, I suggest you read the documentation related to Flink EventTime first, for example [1]

About this question:

What happens if the watermark is same as the timestamp?

Here "timestamp", do you mean the current timestamp of Processing time? If that's the best, it's an ideal state, and it's often difficult to achieve this state, because eventtime always has more or less delay as events are transmitted from the source to the processing system.

Thanks, vino.

[1]:https://ci.apache.org/projects/flink/flink-docs-release-1.6/dev/event_timestamps_watermarks.html

Taher Koitawala <[hidden email]> 于2018年9月14日周五 上午2:07写道：

Hi All,

          Can someone show a good example of how watermarks need to be generated when using EventTime windows?  What happens if the watermark is same as the timestamp?  How does the watermark help in the window to be triggered and what if watermarks are kept behind the currentTimestamps in the assignTimestampsAndWatermarks function.