Flink滚动窗口函数的开窗起始时间计算规则

结论&＃xff1a;窗口的开始时间&＃xff0c;并不一定是最早的记录时间&＃xff0c;而是一个计算出来的时间

Flink的窗口函数起始时间计算公式&＃xff1a;

timestamp - (timestamp - offset &＃43; windowSize) % windowSize
# timestamp为最早时间的记录时间戳
# offset 为参数偏移时间
# windowSize为窗口大小
# 以上计算单位全部统一到毫秒再进行计算

业务代码&＃xff1a; .window(TumblingEventTimeWindows.of(Time.seconds(3L)))

其中滚动窗口api&＃xff1a;TumblingEventTimeWindows of(Time size, Time offset)

源码&＃xff1a;

类&＃xff1a;org.apache.flink.streaming.api.windowing.windows.TimeWindow
public static long getWindowStartWithOffset(long timestamp, long offset, long windowSize) {return timestamp - (timestamp - offset &＃43; windowSize) % windowSize;
}

如果offset不输入&＃xff0c;默认为0&＃xff0c;那么起始时间就是timestamp - timestamp&＃43;windowsize和windowsize的取模&＃xff0c;假定以秒为小单位。

输入时间是个偶数秒T&＃xff0c;windowsize长度为2s&＃xff0c;offset为0的情况下&＃xff0c;那么经过取模部分值为0&＃xff0c;起始时间就是T。

写个小程序计算下启动时间&＃xff1a;

import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZoneOffset;
import java.time.format.DateTimeFormatter;public class WindowStartTimeCalculate {public static void main(String[] args) throws Exception {String[] ss &＃61; {"2020-04-20 10:12:44", "2020-04-20 8:50:44", "2020-04-20 14:12:44", "2020-04-20 18:12:44", "2020-04-20 20:12:44"};for (String date : ss) {cac(Time.days(1L), date, Time.hours(16L));}}/*** &＃64;param w 窗口大小* &＃64;param d 事件时间* &＃64;param o 偏移时间* &＃64;throws Exception*/public static void cac(Time w, String d, Time o) throws Exception {LocalDateTime parse &＃61; LocalDateTime.parse(d, DateTimeFormatter.ofPattern("yyyy-MM-dd H:mm:ss"));long timestamp &＃61; parse.toInstant(ZoneOffset.ofHours(8)).toEpochMilli();long offset &＃61; o.toMilliseconds();long windowSize &＃61; w.toMilliseconds();long startTime &＃61; timestamp - (timestamp - offset &＃43; windowSize) % windowSize;System.out.println("offset:" &＃43; offset &＃43; ", windowSize: " &＃43; windowSize &＃43; ", " &＃43; startTime &＃43; "--" &＃43; LocalDateTime.ofInstant(Instant.ofEpochMilli(startTime), ZoneId.systemDefault()));}
}

窗口1天&＃xff1a;

偏移时间不填写&＃xff0c;那么起始时间是&＃xff1a;2020-04-20T08:00

偏移时间1小时Time.hours(1L)&＃xff0c;那么起始时间是&＃xff1a;2020-04-20T09:00

依次类推...

偏移时间16小时&＃xff0c;则起始时间为&＃xff1a;2020-04-20T00:00

偏移时间23小时&＃xff0c;则起始时间为&＃xff1a;2020-04-20T07:00

窗口3s&＃xff0c;规律不明显&＃xff0c;大部分都是-1s&＃xff1a;

offset:0, windowSize: 3000, record:2020-04-20 10:12:01 ,startTime:2020-04-20T10:12:00
offset:0, windowSize: 3000, record:2020-04-20 08:50:14 ,startTime:2020-04-20T08:50:12
offset:0, windowSize: 3000, record:2020-04-20 14:12:37 ,startTime:2020-04-20T14:12:36
offset:0, windowSize: 3000, record:2020-04-20 18:12:49 ,startTime:2020-04-20T18:12:48
offset:0, windowSize: 3000, record:2020-04-20 20:12:50 ,startTime:2020-04-20T20:12:48

窗口10s&＃xff0c;则起始时间以事件时间个位数为0的时间开始:

offset:0, windowSize: 10000, record:2020-04-20 10:12:01 ,startTime:2020-04-20T10:12:00
offset:0, windowSize: 10000, record:2020-04-20 8:50:14 ,startTime:2020-04-20T08:50:10
offset:0, windowSize: 10000, record:2020-04-20 14:12:37 ,startTime:2020-04-20T14:12:30
offset:0, windowSize: 10000, record:2020-04-20 18:12:49 ,startTime:2020-04-20T18:12:40
offset:0, windowSize: 10000, record:2020-04-20 20:12:50 ,startTime:2020-04-20T20:12:50

窗口5秒&＃xff1a;

offset:0, windowSize: 5000, record:2020-04-20 10:12:01 ,startTime:2020-04-20T10:12:00
offset:0, windowSize: 5000, record:2020-04-20 8:50:14 ,startTime:2020-04-20T08:50:10
offset:0, windowSize: 5000, record:2020-04-20 14:12:37 ,startTime:2020-04-20T14:12:35
offset:0, windowSize: 5000, record:2020-04-20 18:12:49 ,startTime:2020-04-20T18:12:45
offset:0, windowSize: 5000, record:2020-04-20 20:12:50 ,startTime:2020-04-20T20:12:50

窗口为500毫秒&＃xff0c;偏移为空值&＃xff0c;则起始时间就是最早记录&＃xff1a;

offset:0, windowSize: 500, record:2020-04-20 10:12:01 ,startTime:2020-04-20T10:12:01
offset:0, windowSize: 500, record:2020-04-20 8:50:14 ,startTime:2020-04-20T08:50:14
offset:0, windowSize: 500, record:2020-04-20 14:12:37 ,startTime:2020-04-20T14:12:37
offset:0, windowSize: 500, record:2020-04-20 18:12:49 ,startTime:2020-04-20T18:12:49
offset:0, windowSize: 500, record:2020-04-20 20:12:50 ,startTime:2020-04-20T20:12:50