MaxGekk commented on a change in pull request #25998: [SPARK-29328][SQL] Fix
calculation of mean seconds per month
URL: https://github.com/apache/spark/pull/25998#discussion_r331360446
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/EventTimeWatermark.scala
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@@ -28,9 +27,7 @@ object EventTimeWatermark {
val delayKey = "spark.watermarkDelayMs"
def getDelayMs(delay: CalendarInterval): Long = {
- // We define month as `31 days` to simplify calculation.
- val millisPerMonth =
TimeUnit.MICROSECONDS.toMillis(CalendarInterval.MICROS_PER_DAY) * 31
- delay.milliseconds + delay.months * millisPerMonth
+ delay.milliseconds + delay.months * MILLIS_PER_MONTH
Review comment:
I believe any place including this one when we need a duration (in seconds
or its fractions). The difference between `months_between()` and this place is
`months_between` uses month length to calculate fraction of month, and 28 or 31
days per months don't really matter because it impacts on 2nd or 3rd digit in
fractions but here we operate on bigger numbers when months form years. And it
become matter how much days we use per year. Let's say we calculate duration of
10 years which 120 months. If we use 31 days per months, this duration is 31 *
120 = 10 * 372 = 3720 days but if one year is 365.2425, than 1 year = 3652. The
difference is 3720 - 3652 = 68 days or the calculation error is more than 2
months. That's matter I believe.
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