wanlce commented on a change in pull request #21715:
URL: https://github.com/apache/airflow/pull/21715#discussion_r812674759
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File path: airflow/timetables/interval.py
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@@ -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:
> This seems to be always the same as
`self._get_prev(self._get_next(current))`?
>
> Say a CRON schedule runs one every midnight. For this implementation:
>
> * If `current` is at midnight, the return value is at midnight
> * If `current` is on 1am, the return value is at midnight
>
> For `self._get_prev(self._get_next(current))`:
>
> * If `current` is at midnight, `_get_next` returns the next midnight, and
`_get_prev` returns _this_ midnight
> * If `current` is at 1am, `_get_next` returns the next midnight, and
`_get_prev` returns _this_ midnight
>
> And for the timedelta interval, `self._get_prev(self._get_next(current))`
is always `current`.
>
> So if I’m not mistaken, this function is not needed.
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
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