Hi 罗昊, the 2nd picture is meant to visualize the issue of out-of-orderness in general. I'd say it's not referring to a specific strategy.
But one way to interpret the image is using the BoundedOutOfOrderness strategy for watermark generation [1]: You can define an upper bound B for the out-of-orderness. The watermark generator assumes that there's a delay of B, i.e. for an event with timestamp T, no events older than {@code T - B} will follow any more. The delayed watermarks you see in image 2 could be achieved using this bounded out-of-orderness strategy. The usage of watermark strategies is also addressed in the docs [2]. I hope this helps. Matthias [1] https://github.com/apache/flink/blob/c6997c97c575d334679915c328792b8a3067cfb5/flink-core/src/main/java/org/apache/flink/api/common/eventtime/BoundedOutOfOrdernessWatermarks.java#L37 [2] https://ci.apache.org/projects/flink/flink-docs-stable/dev/event_timestamps_watermarks.html#generating-watermarks On Tue, Mar 30, 2021 at 6:26 AM 罗昊 <ly1466671...@163.com> wrote: > Recently I read flink official documents for something about watermarks。 > url: > https://ci.apache.org/projects/flink/flink-docs-release-1.9/dev/event_time.html > there are two pictures illustrating flink watermark mechanism, which > puzzle me mush: > > > The first picture is easy to understand, But in the second, I wonder how > do we get w(11) and w(17)? > As we know, we can define how to generate watermark in the flink job, in > other words, watermarks are generated by certain rules. So what are the > rules that the watermarks are generated in the second pic. > > I look up for almost all offficial documents of different version flink > and they use the same pictures. > It puzzled me much。Is there any explaination? > waiting for your answers ,Thx! >