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https://issues.apache.org/jira/browse/FLINK-3714?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15333441#comment-15333441
 ] 

ASF GitHub Bot commented on FLINK-3714:
---------------------------------------

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

    https://github.com/apache/flink/pull/2093#discussion_r67313976
  
    --- Diff: 
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/WindowOperator.java
 ---
    @@ -132,9 +132,9 @@
     
        /**
         * The allowed lateness for elements. This is used for:
    -    * <li> Deciding if an element should be dropped from a window due to 
lateness. </li>
    -    * <li> Clearing the state of a window if the system time passes
    -    * the {@code window.maxTimestamp + allowedLateness} landmark. </li>
    +    * <ul> Deciding if an element should be dropped from a window due to 
lateness.</ul>
    --- End diff --
    
    Ah, I meant something like this:
    ```
    <ul>
      <li> item 1
      <li> item2
    </ul>
    
    the javadoc syntax is almost similar to HTML, just the closing `</li>` tags 
are missing.


> Add Support for "Allowed Lateness"
> ----------------------------------
>
>                 Key: FLINK-3714
>                 URL: https://issues.apache.org/jira/browse/FLINK-3714
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Streaming
>            Reporter: Aljoscha Krettek
>            Assignee: Kostas Kloudas
>
> As mentioned in 
> https://docs.google.com/document/d/1Xp-YBf87vLTduYSivgqWVEMjYUmkA-hyb4muX3KRl08/edit#
>  we should add support for an allowed lateness setting.
> This includes several things:
>  - API for setting allowed lateness
>  - Dropping of late elements 
>  - Garbage collection of windows state/timers
> Depending on whether the {{WindowAssigner}} assigns windows based on event 
> time or processing time we have to adjust the GC behavior. For event-time 
> windows "allowed lateness" makes sense and we should garbage collect after 
> this expires. For processing-time windows "allowed lateness" does not make 
> sense and we should always GC window state/timers at the end timestamp of a 
> processing-time window. I think that we need a method for this on 
> {{WindowAssigner}} that allows to differentiate between event-time windows 
> and processing-time windows: {{boolean WindowAssigner.isEventTime()}}.



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