[jira] [Closed] (FLINK-12714) confusion about flink time window TimeWindow#getWindowStartWithOffset

["Wenshuai Hou (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-12714?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wenshuai Hou closed FLINK-12714.
--------------------------------
    Resolution: Fixed

just saw this in flink doc.

For example, with an event-time-based windowing strategy that creates non-overlapping (or tumbling) windows every 5 minutes and has an allowed lateness of 1 min, Flink will create a new window for the interval between {{12:00}} and {{12:05}} when the first element with a timestamp that falls into this interval arrives, and it will remove it when the watermark passes the {{12:06}} timestamp

> confusion about flink time window TimeWindow#getWindowStartWithOffset
> ---------------------------------------------------------------------
>
>                 Key: FLINK-12714
>                 URL: https://issues.apache.org/jira/browse/FLINK-12714
>             Project: Flink
>          Issue Type: Improvement
>          Components: flink-contrib
>    Affects Versions: 1.8.0
>            Reporter: Wenshuai Hou
>            Priority: Minor
>
>  
> hi flink team, i think the flink doc on how time windows are created and the javadoc of related method is a little confusing. They give me the impression that the window-start equals to the timestamp of the first event assigned to that window, however the window-start is actually quantized by the windowSize, see links below. Is this the intention or is this a mistake? If it's intended, can we please leave a comment in flink doc somewhere to make this more clear? I spent 5 hours wondering why my flink tests fail until i find that method. 
>  
> Thanks 
> Wen 
>  
> links: 
> ================
>  
> The flink doc from here : [https://ci.apache.org/projects/flink/flink-docs-stable/dev/stream/operators/windows.html#window-lifecycle] 
> > In a nutshell, a window is *created* as soon as the first element that should belong to this window arrives
>  
> the java doc of this method:  org.apache.flink.streaming.api.windowing.windows.TimeWindow#getWindowStartWithOffset
>  
>  
> {code:java}
> /**
>  * Method to get the window start for a timestamp.
>  *
>  * @param timestamp epoch millisecond to get the window start.
>  * @param offset The offset which window start would be shifted by.
>  * @param windowSize The size of the generated windows.
>  * @return window start
>  */
> public static long getWindowStartWithOffset(long timestamp, long offset, long windowSize) {
> {code}
>  
>  
>  
>  



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