[FLINK-12714] confusion about flink time window TimeWindow#getWindowStartWithOffset

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 1.8.0
• Component/s: flink-contrib
• Assignee: Unassigned
• Reporter: Wenshuai Hou
• Created: 03/Jun/19 23:19
• Updated: 18/Jun/19 17:26
• Resolved: 18/Jun/19 17:26

Description

 

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

 

 

/**
 * 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) {