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https://issues.apache.org/jira/browse/FLINK-5972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15936537#comment-15936537
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ASF GitHub Bot commented on FLINK-5972:
---------------------------------------

Github user aljoscha commented on a diff in the pull request:

    https://github.com/apache/flink/pull/3587#discussion_r107446618
  
    --- Diff: 
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/WindowOperator.java
 ---
    @@ -574,7 +588,7 @@ private void emitWindowContents(W window, ACC contents) 
throws Exception {
         *
         * @param element skipped late arriving element to side output
         */
    -   private void sideOutput(StreamRecord<IN> element){
    +   protected void sideOutput(StreamRecord<IN> element){
    --- End diff --
    
    Same as for `lateDataOutputTag`. It's used by the `EvictingWindowOperator`. 
I can also make it package private.


> 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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