MaxGekk opened a new pull request #28809: URL: https://github.com/apache/spark/pull/28809
### What changes were proposed in this pull request? Fix the bug in microseconds rebasing during transitions from one standard time zone offset to another one. In the PR, I propose to change the implementation of `rebaseGregorianToJulianMicros` which performs rebasing via local timestamps. In the case of overlapping: 1. Check that the original instant belongs to earlier or later instant of overlapped local timestamp. 2. If it is an earlier instant, take zone and DST offsets from the previous day otherwise 3. Set time zone offsets to Julian timestamp from the next day. Note: The fix assumes that transitions cannot happen more often than once per 2 days. ### Why are the changes needed? Current implementation handles timestamps overlapping only during daylight saving time but overlapping can happen also during transition from one standard time zone to another one. For example in the case of `Asia/Hong_Kong`, the time zone switched from `Japan Standard Time` (UTC+9) to `Hong Kong Time` (UTC+8) on _Sunday, 18 November, 1945 01:59:59 AM_. The changes allow to handle the special case as well. ### Does this PR introduce _any_ user-facing change? It might affect micros rebasing in before common era when not-optimised version of `rebaseGregorianToJulianMicros()` is used directly. ### How was this patch tested? 1. By existing tests in `DateTimeUtilsSuite`, `RebaseDateTimeSuite`, `DateFunctionsSuite`, `DateExpressionsSuite` and `TimestampFormatterSuite`. 2. Added new test to `RebaseDateTimeSuite` 3. Regenerated `gregorian-julian-rebase-micros.json` with the step of 30 minutes, and got the same JSON file. The JSON file isn't affected because previously it was generated with the step of 1 week. And the spike in diffs/switch points during 1 hour of timestamp overlapping wasn't detected. Authored-by: Max Gekk <max.g...@gmail.com> Signed-off-by: Wenchen Fan <wenc...@databricks.com> (cherry picked from commit c259844df8b6690b752a1c67b241de2981cdb5fe) Signed-off-by: Max Gekk <max.g...@gmail.com> ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org
