[GitHub] [spark] cloud-fan edited a comment on pull request #28787: [SPARK-31959][SQL][test-java11] Fix Gregorian-Julian micros rebasing while switching standard time zone offset

[GitBox <gi...@apache.org>]

cloud-fan edited a comment on pull request #28787:
URL: https://github.com/apache/spark/pull/28787#issuecomment-643086118


   More context:
   
   To do datetime rebase more efficiently, we put the diffs between two calendars in JSON files, to avoid calculating the diffs every time.
   
   To generate the JSON file, we run the rebase function for all the datetime values from year 0001 to year 2037, using one week as the step. This is not accurate and we miss diffs during some short period.
   
   The good news is: although the JSON files do not match the rebase function, they are correct. The rebase function has a bug. We have a random test to make sure the rebase function matches the generated JSON files, and that's why we found this bug.
   
   That said, this is not a real bug as it doesn't affect end users, but it makes the test flaky.


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