郭元方 created FLINK-26307:
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Summary: 当事件时间在（Long.MIN_VALUE ，-windowsize）时，不能正确的求到开启窗口的起始时间
Key: FLINK-26307
URL: https://issues.apache.org/jira/browse/FLINK-26307
Project: Flink
Issue Type: Improvement
Components: API / DataStream
Reporter: 郭元方
对于底层实现窗口时，求其起始时间的方法：
public static long getWindowStartWithOffset(long timestamp, long offset, long
windowSize) {
return timestamp - (timestamp - offset + windowSize) % windowSize;
}
例如：窗口大小为10，事件时间分别为1s，7s，12s得到的起始时间，正确。
=> timestamp - (timestamp - offset + windowSize) % windowSize
=> 1 - (1 -0 + 10) % 10 => start = 0s
=> 7 - (7 -0 + 10) % 10 => start = 0s
=> 12 - (12 - 0 + 10) % 10 => start = 10s
但是当事件时间为
-1s，-7s，-12s，-15s，-17s，-19s时，窗口的起始时间却也都为-10s，是否由于在java中的取余规则，正数对正数取余的商值向0逼近，而负数对正数取余的商值也向0逼近
导致该算法对事件时间在（Long.MIN_VALUE，-windowsize）的这个范围内的数据不能正确的求到开启窗口的起始时间呢？
=> timestamp - (timestamp - offset + windowSize) % windowSize
=> -1 - (-1 -0 + 10) % 10 => start = -10s
=> -7 - (-7 -0 + 10) % 10 => start = -10s
=> -12 - (-12 - 0 + 10) % 10 => start = -10s
=> -15 - (-15 - 0 + 10) % 10 => start = -10s
=> -17 - (-17 - 0 + 10) % 10 => start = -10s
=> -19 - (-19 - 0 + 10) % 10 => start = -10s
和同学邓子琦的讨论，并没有经历过业务，所以此处事件时间求到了负值，现实世界来说不一定，但逻辑上来说应该可以求到负值吧。
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