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https://issues.apache.org/jira/browse/FLINK-3375?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15139159#comment-15139159
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Zach Cox commented on FLINK-3375:
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Like [~shikhar] I will also have event producers on different machines (with
independent clocks) sending messages to the same Kafka topic partitions. So
events from the same producer are ordered, but in general events in each
partition are somewhat out-of-order. I have full control over these producers,
and have considered having them emit periodic watermarks. Would be nice to also
have the option for the FlinkKafkaConsumer to use watermarks embedded directly
in the Kafka topic, instead of just trying to extract them from events.
> 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
> 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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