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https://issues.apache.org/jira/browse/SPARK-31449?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Maxim Gekk updated SPARK-31449:
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Issue Type: Improvement (was: Question)
> Investigate the difference between JDK and Spark's time zone offset
> calculation
> -------------------------------------------------------------------------------
>
> Key: SPARK-31449
> URL: https://issues.apache.org/jira/browse/SPARK-31449
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.4.5
> Reporter: Maxim Gekk
> Priority: Major
>
> Spark 2.4 calculates time zone offsets from wall clock timestamp using
> `DateTimeUtils.getOffsetFromLocalMillis()` (see
> https://github.com/apache/spark/blob/branch-2.4/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala#L1088-L1118):
> {code:scala}
> private[sql] def getOffsetFromLocalMillis(millisLocal: Long, tz: TimeZone):
> Long = {
> var guess = tz.getRawOffset
> // the actual offset should be calculated based on milliseconds in UTC
> val offset = tz.getOffset(millisLocal - guess)
> if (offset != guess) {
> guess = tz.getOffset(millisLocal - offset)
> if (guess != offset) {
> // fallback to do the reverse lookup using java.sql.Timestamp
> // this should only happen near the start or end of DST
> val days = Math.floor(millisLocal.toDouble / MILLIS_PER_DAY).toInt
> val year = getYear(days)
> val month = getMonth(days)
> val day = getDayOfMonth(days)
> var millisOfDay = (millisLocal % MILLIS_PER_DAY).toInt
> if (millisOfDay < 0) {
> millisOfDay += MILLIS_PER_DAY.toInt
> }
> val seconds = (millisOfDay / 1000L).toInt
> val hh = seconds / 3600
> val mm = seconds / 60 % 60
> val ss = seconds % 60
> val ms = millisOfDay % 1000
> val calendar = Calendar.getInstance(tz)
> calendar.set(year, month - 1, day, hh, mm, ss)
> calendar.set(Calendar.MILLISECOND, ms)
> guess = (millisLocal - calendar.getTimeInMillis()).toInt
> }
> }
> guess
> }
> {code}
> Meanwhile, JDK's GregorianCalendar uses special methods of ZoneInfo, see
> https://github.com/AdoptOpenJDK/openjdk-jdk8u/blob/aa318070b27849f1fe00d14684b2a40f7b29bf79/jdk/src/share/classes/java/util/GregorianCalendar.java#L2795-L2801:
> {code:java}
> if (zone instanceof ZoneInfo) {
> ((ZoneInfo)zone).getOffsetsByWall(millis, zoneOffsets);
> } else {
> int gmtOffset = isFieldSet(fieldMask, ZONE_OFFSET) ?
> internalGet(ZONE_OFFSET) :
> zone.getRawOffset();
> zone.getOffsets(millis - gmtOffset, zoneOffsets);
> }
> {code}
> Need to investigate are there any differences in results between 2 approaches.
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