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 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!
>
