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[jira] [Created] (FLINK-9857) Processing-time timers fire too early

Aljoscha Krettek created FLINK-9857:

             Summary: Processing-time timers fire too early
                 Key: FLINK-9857
                 URL: https://issues.apache.org/jira/browse/FLINK-9857
             Project: Flink
          Issue Type: Bug
          Components: DataStream API
    Affects Versions: 1.5.1, 1.4.2, 1.3.4, 1.6.0
            Reporter: Aljoscha Krettek
             Fix For: 1.5.2, 1.6.0

The firing of processing-time timers is off by one. This leads to problems in edge cases, as discovered [here (mailing list)|https://lists.apache.org/thread.html/e49748fa5fa1c9217b9dfb65eea7a37af1f2895c769528e77a1a93fa@%3Cuser.flink.apache.org%3E] when elements arrive at the timestamp that is the end of the window.

The problem is [here (github)|https://github.com/apache/flink/blob/79b38f8f9a79b917d525842cf46087c5b8c40f3d/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/operators/HeapInternalTimerService.java#L231]. For event-time, we fire timers when the watermark is >= the timestamp, this is correct because a watermark T says that we will not see elements with a timestamp smaller or equal to T. For processing time, a time of T does not say that we won't see an element with timestamp T, which makes processing-time timers fire one ms too early.

I think we can fix it by turning that {{<=}} into a {{<}}.

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