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https://issues.apache.org/jira/browse/FLINK-5972?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Aljoscha Krettek updated FLINK-5972:
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Fix Version/s: 1.2.1
> Don't allow shrinking merging windows
> -------------------------------------
>
> Key: FLINK-5972
> URL: https://issues.apache.org/jira/browse/FLINK-5972
> Project: Flink
> Issue Type: Bug
> Components: DataStream API
> Affects Versions: 1.1.0, 1.2.0, 1.3.0
> Reporter: Aljoscha Krettek
> Priority: Blocker
> Fix For: 1.3.0, 1.2.1
>
>
> A misbehaving {{MergingWindowAssigner}} can cause a merge that results in a
> window that is smaller than the span of all the merged windows. This, in
> itself is not problematic. It becomes problematic when the end timestamp of a
> window that was not late before merging is now earlier than the watermark
> (the timestamp is smaller than the watermark).
> There are two choices:
> - immediately process the window
> - drop the window
> processing the window will lead to late data downstream.
> The current behaviour is to silently drop the window but that logic has a
> bug: we only remove the dropped window from the {{MergingWindowSet}} but we
> don't properly clean up state and timers that the window still (possibly)
> has. We should fix this bug in the process of resolving this issue.
> We should either just fix the bug and still silently drop windows or add a
> check and throw an exception when the end timestamp falls below the watermark.
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