[GitHub] [airflow] wanlce commented on a change in pull request #21715: Fix incorrect data_interval_start due to scheduling time change

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

wanlce commented on a change in pull request #21715:
URL: https://github.com/apache/airflow/pull/21715#discussion_r812673361



##########
File path: airflow/timetables/interval.py
##########
@@ -211,6 +217,17 @@ def _align(self, current: DateTime) -> DateTime:
             return next_time
         return current
 
+    def _prev_align(self, current: DateTime) -> DateTime:
+        """Get the prev scheduled time.
+
+        This is ``current - interval``, unless ``current`` falls right on the
+        interval boundary, when ``current`` is returned.
+        """
+        prev_time = self._get_prev(current)
+        if self._get_next(prev_time) != current:
+            return prev_time
+        return current

Review comment:
       They are different ha
   
   For self._prev_align()
   - If current is at 1am, the return value is at midnight 
   
   For self._align()  
   - If current is at 1am, the return value is next midnight.
   
   It is correct that `data_schedule_start` is equal to the `data_schedule_end` of the previous one when no scheduling time changes. However, when the scheduling time changes, The first `data_schedule_start` for a new schedule may not be the same as the `data_schedule_end` before the schedule was changed
   ![2022-02-23_16-55](https://user-images.githubusercontent.com/55907021/155287695-aa251f60-df19-43e3-9d12-d8fb24be36c8.png)
   
   
   




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