Github user liancheng commented on the pull request:
https://github.com/apache/spark/pull/8400#issuecomment-134548748
Just would like to point out that our original `DateTimeUtils` doesn't do
Julian date conversion right either. Here is a `spark-shell` snippet executed
against
https://github.com/apache/spark/commit/053d94fcf32268369b5a40837271f15d6af41aa4:
```scala
import java.sql._
import java.util._
import org.apache.hadoop.hive.ql.io.parquet.timestamp._
import org.apache.spark.sql.catalyst.util._
TimeZone.setDefault(TimeZone.getTimeZone("GMT"))
val timestamp = Timestamp.valueOf("1970-01-01 00:00:00")
val hiveNanoTime = NanoTimeUtils.getNanoTime(timestamp, false)
val hiveJulianDay = hiveNanoTime.getJulianDay
val hiveTimeOfDayNanos = hiveNanoTime.getTimeOfDayNanos
println(
s"""Hive converts "$timestamp" to Julian timestamp:
|(julianDay=$hiveJulianDay, timeOfDayNanos=$hiveTimeOfDayNanos)
""".stripMargin)
val (sparkJulianDay, sparkTimeOfDayNanos) =
DateTimeUtils.toJulianDay(DateTimeUtils.fromJavaTimestamp(timestamp))
println(
s"""Spark converts "$timestamp" to Julian timestamp:
|(julianDay=$sparkJulianDay, timeOfDayNanos=$sparkTimeOfDayNanos)
""".stripMargin)
```
The result is:
```
Hive converts "1970-01-01 00:00:00.0" to Julian timestamp:
(julianDay=2440588, timeOfDayNanos=0)
Spark converts "1970-01-01 00:00:00.0" to Julian timestamp:
(julianDay=2440588, timeOfDayNanos=43200000000000)
```
while the correct answer should be:
```
(julianDay=2440587, timeOfDayNanos=43200000000000)
```
So Hive is 12 hours later than the expected Julian timestamp, while we were
24 hours later :)
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