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https://issues.apache.org/jira/browse/FLINK-3428?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15179772#comment-15179772
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ASF GitHub Bot commented on FLINK-3428:
---------------------------------------
Github user kl0u commented on a diff in the pull request:
https://github.com/apache/flink/pull/1764#discussion_r55020209
--- Diff:
flink-streaming-scala/src/main/scala/org/apache/flink/streaming/api/scala/DataStream.scala
---
@@ -750,6 +750,34 @@ class DataStream[T](stream: JavaStream[T]) {
}
/**
+ * Assigns timestamps to the elements in the data stream and
periodically creates
+ * watermarks to signal event time progress.
+ *
+ * This method is used for cases where the programmer wants the
Watermarks emitted in
+ * the stream to lag behind the maximum timestamp seen so far by a
fixed period of time.
+ *
+ * For more general cases, use the general methods
+ * [[assignTimestampsAndWatermarks(AssignerWithPeriodicWatermarks)]]
+ * and
[[assignTimestampsAndWatermarks(AssignerWithPunctuatedWatermarks)]].
+ *
+ * @param fixedWatermarkTrailingPeriod the fixed lag between the
currently emitted
+ * watermark and the maximum
timestamp seen so far.
+ * @param extractor the method to extracts the timestamp from a given
record.
+ */
+ @PublicEvolving
+ def
assignTimestampsWithAFixedPeriodTrailingWatermark(fixedWatermarkTrailingPeriod:
Long,
--- End diff --
It is true, although I added it because there was already a method for the
ascending one. If there is a consensus, I can remove it.
> 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: Klou
>
> 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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