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https://issues.apache.org/jira/browse/FLINK-3435?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15150676#comment-15150676
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Stephan Ewen commented on FLINK-3435:
-------------------------------------
Given that this is quite fundamental, I think it becomes an issue to be
resolved before the next release candidate.
> Change interplay of Ingestion Time and Event Time
> -------------------------------------------------
>
> Key: FLINK-3435
> URL: https://issues.apache.org/jira/browse/FLINK-3435
> Project: Flink
> Issue Type: Improvement
> Components: Streaming
> Affects Versions: 0.10.2
> Reporter: Stephan Ewen
> Fix For: 1.0.0
>
>
> Currently, "EventTime" and "IngestionTime" are completely the same.
> For both happens the following:
> - Sources generate ingestion time timestamps and watermarks
> - If a user adds a manual timestamp extractor / watermark generator, then
> those override the ingestion time timestamps and watermarks
> - That implies that event time on a certain input falls back to ingestion
> time, if one forgets (or incorrectly uses) the timestamp extractors
> - Also, Ingestion Time and Event Time simply mix if some inputs have
> timestamp assigners, and others have not.
> This behavior is quite tricky to understand. After some discussions with
> [~aljoscha] and [~rmetzger], we suggest to change it the following way.
> 1. On Ingestion Time, the timestamps and watermarks are generated as they
> are now.
> 2. On event time, no default timestamps and watermarks are generated. If a
> user does not implement a timestamp extractor / watermark generator, then the
> event time operations will fail fast.
> 3. If one wants to use ingestion time on event time settings (mix), one can
> use an explicit "WallClockTimetampsAndWatermark" generator.
> 4. Later, the "Ingestion Time" settings should automatically disable and
> user-defined timestamp extractors / assigners.
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