cloud-fan commented on a change in pull request #28166:
[SPARK-31359][DOC][followup] improve code comments in RebaseDateTime
URL: https://github.com/apache/spark/pull/28166#discussion_r406136677
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/RebaseDateTime.scala
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@@ -256,14 +270,23 @@ object RebaseDateTime {
}
/**
- * Converts the given microseconds to a local date-time in UTC time zone in
the hybrid
- * calendar (Julian + Gregorian since 1582-10-15), interprets the result as
a local date-time
- * in Proleptic Gregorian calendar in UTC time zone. And takes microseconds
since the epoch
- * from the Gregorian timestamp.
+ * Converts the given number of microseconds since the epoch
'1970-01-01T00:00:00Z', to a local
+ * date-time in Julian calendar with timezone identified by `zoneId`,
interprets the result as a
+ * local date-time in Proleptic Gregorian calendar with the same timezone,
and takes microseconds
+ * since the epoch from the Gregorian local date-time.
+ *
+ * This is used to guarantee backward compatibility, as Spark 2.4 and
earlier versions use
+ * Julian calendar for dates before 1582-10-15, while Spark 3.0 and later
use Proleptic Gregorian
+ * calendar. See SPARK-26651.
+ *
+ * For example:
+ * Julian calendar: 1582-01-01 00:00:00.123456 -> -12243196799876544
+ * Proleptic Gregorian calendar: 1582-01-01 00:00:00.123456 ->
-12244061221876544
+ * The code below converts -12243196799876544 to -12244061221876544.
*
* @param zoneId The time zone ID at which the rebasing should be performed.
* @param micros The number of microseconds since the epoch
'1970-01-01T00:00:00Z'
- * in the hybrid calendar (Julian + Gregorian). It can be
negative.
+ * in the Julian calendar. It can be negative.
Review comment:
The rebase mostly happens before 1582, so Julian calenday is OK. The method
name is also `JulianToGregorian`.
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