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https://issues.apache.org/jira/browse/FLINK-6205?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15947604#comment-15947604
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ASF GitHub Bot commented on FLINK-6205:
---------------------------------------
Github user dawidwys commented on a diff in the pull request:
https://github.com/apache/flink/pull/3644#discussion_r108742662
--- Diff: docs/dev/libs/cep.md ---
@@ -711,6 +711,57 @@ DataStream[Either[TimeoutEvent, ComplexEvent]] result
= patternStream.flatSelect
</div>
</div>
+### Handling Lateness in Event Time
+
+In `CEP` the order in which elements are processed matters. To this end
and when working in event time, an incoming
--- End diff --
I don't get the first part of the sentence : "To this end and when working
in event time"
> Put late elements in side output.
> ---------------------------------
>
> Key: FLINK-6205
> URL: https://issues.apache.org/jira/browse/FLINK-6205
> Project: Flink
> Issue Type: Bug
> Components: CEP
> Affects Versions: 1.3.0
> Reporter: Kostas Kloudas
> Assignee: Kostas Kloudas
> Fix For: 1.3.0
>
>
> Currently the CEP library had a somehow fuzzy way to handle late events.
> Essentially:
> 1) it accepts all events (late and early)
> 2) it sorts them based on event time
> 3) whenever a watermark arrives, it feeds them into the NFA.
> This does not respect event time, as late events are still processed.
> In addition, given that the order in which elements are processed matters,
> this could lead to wrong results as events may be processed by the NFA
> out-of-order with respect to their timestamps.
> This issue proposes to assume correctness of the watermark and consider as
> late, events that arrive having a timestamp smaller than that of the last
> seen watermark. In addition, late events are not silently dropped, but the
> user can specify to send them to a side output, as done in the case of the
> {{WindowOperator}}.
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