Aljoscha Krettek created FLINK-9857:
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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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