fsk119 commented on a change in pull request #14111:
URL: https://github.com/apache/flink/pull/14111#discussion_r528648191
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File path: docs/dev/table/connectors/kafka.md
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@@ -249,6 +249,15 @@ Besides enabling Flink's checkpointing, you can also
choose three different mode
Please refer to [Kafka documentation]({% link dev/connectors/kafka.md
%}#kafka-producers-and-fault-tolerance) for more caveats about delivery
guarantees.
+### Per-partition-watermark Source
+
+Flink supports to emit per-partition-watermark for Kafka. Using this feature,
watermarks are generated inside the Kafka consumer. The per-partition-watermark
are merged in
+the same way as watermarks are merged on stream shuffles. The output watermark
of the source is determined by the minimum watermark among the partitions it
reads. Considering a watermark assigner
+advance the watermark according to the event-time on the records. If some
partitions in the topics are idle, the watermark assigner will not advance. You
can alleviate this problem by
+setting appropriate [idelness timeouts]({{ site.baseurl
}}/dev/event_timestamps_watermarks.html#dealing-with-idle-sources).
Review comment:
Could you give a bad case about this feature? With this feature, we can
get more fine-grained watermark. Only some partition are idle, the watermark
assigner doesn't advance itself. However, we can set idle timeout to solve this
problem.
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