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https://issues.apache.org/jira/browse/FLINK-3375?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15217751#comment-15217751
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ASF GitHub Bot commented on FLINK-3375:
---------------------------------------

Github user kl0u commented on the pull request:

    https://github.com/apache/flink/pull/1839#issuecomment-203354870
  
    This PR is for FLINK-3375.
    Please review.


> Allow Watermark Generation in the Kafka Source
> ----------------------------------------------
>
>                 Key: FLINK-3375
>                 URL: https://issues.apache.org/jira/browse/FLINK-3375
>             Project: Flink
>          Issue Type: Improvement
>          Components: Kafka Connector
>    Affects Versions: 1.0.0
>            Reporter: Stephan Ewen
>            Assignee: Kostas Kloudas
>             Fix For: 1.0.0
>
>
> It is a common case that event timestamps are ascending inside one Kafka 
> Partition. Ascending timestamps are easy for users, because they are handles 
> by ascending timestamp extraction.
> If the Kafka source has multiple partitions per source task, then the records 
> become out of order before timestamps can be extracted and watermarks can be 
> generated.
> If we make the FlinkKafkaConsumer an event time source function, it can 
> generate watermarks itself. It would internally implement the same logic as 
> the regular operators that merge streams, keeping track of event time 
> progress per partition and generating watermarks based on the current 
> guaranteed event time progress.



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