mai-nakagawa commented on PR #23662:
URL: https://github.com/apache/airflow/pull/23662#issuecomment-1136719955
Thanks for your comment, @uranusjr.
> Instead of inheriting `CronDataIntervalTimetable` directly, I would prefer
the common logic be extracted out to a superclass, which both timetable clases
inherit.
Agree.
> I feel this class should also schedule tasks differently. As described in
AIP-39, a common use case for this kind of timetables is for tasks to run at
the end of each weekday (say 5pm). This means the cron expression should
express the _end_ of a data interval, instead of the beginning like
`CronDataIntervalTimetable`. In other words, `PlainCronTimetable("0 5 * *
1-5")` triggers a DAG run at 5pm on each Monday through Friday, with each run
covering the interval between the triggering time of this and the previous run.
This would mean we need more different logic between this class and
`CronDataIntervalTimetable`.
I don't fully understand. In my understanding, even with the current
`CronDataIntervalTimetable`, we express the _end_ (not the _beginning_) of a
data interval. For example, `CronDataIntervalTimetable("0 5 * * MON-FRI")`
triggers a DAG run at 5am on each Monday through Friday. Kindly correct me if
I'm wrong.
However, I agree `CronTimetable` (instead of `CronDataIntervalTimetable`),
which ignores the idea of "data interval", would be appreciated. It means
`execution_date`, `data_interval_start` and `data_interval_end` will be the
same - what time the DAG run starts. It will show what time the next DAG Run
will be triggered exactly in the Web UI:
> Honestly the current behaviour sounds like a bug to me, and arguably we
might want to just fix that instead of introducing a new timetable. Most users
probably don’t really care about that first run, and we could introduce a
custom timetable to support the legacy first run behaviour. (The main
difference is, I think we should change the `schedule_interval` behaviour.)
I personally okay with your idea though I'm not too sure if most users don't
really care about the first run.
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