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https://issues.apache.org/jira/browse/FLINK-3428?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15223915#comment-15223915
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ASF GitHub Bot commented on FLINK-3428:
---------------------------------------

Github user kl0u commented on the pull request:

    https://github.com/apache/flink/pull/1764#issuecomment-205233984
  
    Hello @StephanEwen 
    I totally agree with the comments.
    I rearranged the extractors and integrated your comments on the 
documentation.
    Please review.


> Add fixed time trailing timestamp/watermark extractor
> -----------------------------------------------------
>
>                 Key: FLINK-3428
>                 URL: https://issues.apache.org/jira/browse/FLINK-3428
>             Project: Flink
>          Issue Type: Improvement
>            Reporter: Robert Metzger
>            Assignee: Kostas Kloudas
>
> Flink currently provides only one build-in timestamp extractor, which assumes 
> strictly ascending timestamps. In real world use cases, timestamps are almost 
> never strictly ascending.
> Therefore, I propose to provide an utility watermark extractor which is 
> generating watermarks with a fixed-time trailing.
> The implementation should keep track of the highest event-time seen so far 
> and subtract a fixed amount of time from that event time.
> This way, users can for example specify that the watermarks should always 
> "lag behind" 10 minutes.



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