Make it possible to change the default cron timetable

[collinmcnulty]

Closes #34695 .

Adds the setting scheduler.legacy_cron_data_intervals with a default of True (CronDataIntervalTimetable). If it is set to False, the CronTriggerTimetable is used for any bare cron strings.

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[uranusjr]

I feel this is a good idea. It may be worthwhile to expand this a bit to be a full “policy” that handles all kinds of non-timetable/dataset inputs, but that could be expanded later, with this maybe retained for convenience or compatibility.

[collinmcnulty]

Yes, linked issue was wrong, I have now fixed it.

[collinmcnulty]

I am not sure how best to unit test this.

[uranusjr]

Because conf is not called conf in this file

airflow/airflow/models/dag.py

Line 80 in 03a305f

from airflow.configuration import conf as airflow_conf, secrets_backend_list

[collinmcnulty]

@uranusjr I've responded to all review comments.

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed in 5 days if no further activity occurs. Thank you for your contributions.

[collinmcnulty]

I'm pretty sure the failing test is spurious. I do not have permission to re-run it.

[potiuk]

I'm pretty sure the failing test is spurious. I do not have permission to re-run it.

Neither do we once there is conflict with another PR. You need to rebase and solve the conflicts in order to re-run the tests.

[potiuk]

[potiuk]

This is fine, however I think we need to add a bit more education for our users on it. We have about a million configuration parameters and expecting the users to read them and understand them in order to know they can change such a basic behavioud of Airlfow is s mostly wishful thinking.

I think this deserve some more important and prominent explanation soemwhere close to "Concepts" - possibly at the "Concept" page itself.

I think we should have there a chapter entitled:

"How Airflow Schedule Cron-like schedules" - where we should explain how it was, originally and how users can change it to get to more "familiar" scheduling semantics. This is a bit too important change to mention it in only in configuration parameter description IMHO

[collinmcnulty]

I fully agree. Would you be ok with that being a separate PR?

[potiuk]

I fully agree. Would you be ok with that being a separate PR?

Sure. That's why I did not request changes :)