MaxGekk commented on a change in pull request #27807: [SPARK-31076][SQL]
Convert Catalyst's DATE/TIMESTAMP to Java Date/Timestamp via local date-time
URL: https://github.com/apache/spark/pull/27807#discussion_r390251052
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File path:
sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveInspectors.scala
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@@ -1012,7 +1046,27 @@ private[hive] trait HiveInspectors {
}
private def getDateWritable(value: Any): hiveIo.DateWritable =
- if (value == null) null else new
hiveIo.DateWritable(value.asInstanceOf[Int])
+ if (value == null) {
+ null
+ } else {
+ // Rebasing days since the epoch to store the same number of days
+ // as by Spark 2.4 and earlier versions. Spark 3.0 switched to
+ // Proleptic Gregorian calendar (see SPARK-26651), and as a consequence
of that,
+ // this affects dates before 1582-10-15. Spark 2.4 and earlier versions
use
+ // Julian calendar for dates before 1582-10-15. So, the same local date
may
+ // be mapped to different number of days since the epoch in different
calendars.
+ // For example:
+ // Proleptic Gregorian calendar: 1582-01-01 -> -141714
+ // Julian calendar: 1582-01-01 -> -141704
+ // The code below converts -141714 to -141704.
Review comment:
Gregorian year is short than Julian year: 365.2425 days vs 365.25 days, so
the same local date in Gregorian calendar requires less days in Julian calendar.
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