Wenshuai Hou created FLINK-12714:
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Summary: 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
hi flink team, i think the flink doc on how time windows are created an 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? 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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