I'm in favor of doing that, but then exposing new variables of "interval_start" and "interval_end", etc. so that people write clearer-looking at-a-glance DAGs
On Fri, Aug 23, 2019 at 10:39 AM Dan Davydov <ddavy...@twitter.com.invalid> wrote: > What are people's feelings on changing the default execution to schedule > interval start and communicating this to existing users in the Updating > notes so that they can preserve the old behavior? Could potentially cause > headaches for users who don't read the notes but I think it might make > sense to bite the bullet at some point for more intuitive behavior overall > for new users. > > On Fri, Aug 23, 2019 at 10:29 AM Dan Davydov <ddavy...@twitter.com> wrote: > > > I am for this change, since I feel like in general the start of the > > interval is more intuitive (I have been working on Airflow for 3 years > and > > this still trips me up). That being said I'm not sure how I feel about > > allowing customization at DAG level instead of cluster level as it makes > it > > harder to make assumptions about DAGs on the cluster for ops, though > maybe > > this isn't a huge deal given there are tools available that show you why > > tasks aren't running. > > > > I agree with Bole that we should communicate recommended migration > > strategies if they can't be done automatically. > > > > I don't think I'm a fan for arbitrary customization of the interval via a > > callback, my feeling is this would not provide significant value and > could > > be an ops nightmare. > > > > On Fri, Aug 23, 2019 at 9:11 AM Jarek Potiuk <jarek.pot...@polidea.com> > > wrote: > > > >> DST: I recall problems with DST especially when the hour goes back and > the > >> daily schedule time technically occurs twice the same day or does not > >> occur > >> at all. We have some code that chooses arbitrary the first occurence in > >> the > >> latter case (there was a problem that it worked differently python 3.6 > vs > >> 3.5 (!). But also the case when we move forward is an interesting one. I > >> am > >> not 100% it will work correctly after changing the scheduling mechanisms > >> but it's rather easy to test and there is no harm adding it. > >> There is a DST-specific logic implemented in our next/previous run > >> calculation and I imagine it could get wrong. > >> > >> The tests I am talking about: > >> > >> > DagTest.test_following_previous_schedule_daily_dag_CEST_to_CET/DagTest.test_following_previous_schedule_daily_dag_CET_to_CEST. > >> > >> Re: arbitrary customisation/converting DAGs. I think there is no need to > >> convert existing dags - the default behaviour remains as it is as far > as I > >> understand. And this flag is much simpler to understand and reason about > >> than arbitrary function and it corresponds to real business cases: > >> > >> 1) schedule_at_interval_end = True -> wait for the data to be ready for > >> the > >> interval (current/default behaviour related to processing batches of > data) > >> 2) schedule_at_interval_end = False -> CRON-like behaviour where we > simply > >> run arbitrary operation in regular intervals (more intuitive for people > >> who > >> are used to CRON-like jobs) > >> > >> You can always build your schedule differently if you need something > >> "in-between" IMHO. > >> > >> J. > >> > >> > >> > >> > >> On Fri, Aug 23, 2019 at 8:44 AM James Meickle > >> <jmeic...@quantopian.com.invalid> wrote: > >> > >> > This is a change to one of Airflow's core concepts, and it would > >> require a > >> > lot of work for existing DAGs to cut over to it. Given that, my > personal > >> > preference would be to allow arbitrary customization rather than just > a > >> bit > >> > toggle. Such as allowing passing in a mapping function: given an > >> interval's > >> > start date and end date, when should it be executed? > >> > > >> > On Fri, Aug 23, 2019 at 8:24 AM Jarek Potiuk < > jarek.pot...@polidea.com> > >> > wrote: > >> > > >> > > Happy for it as well. There are a number of cases where scheduling > at > >> > start > >> > > makes more sense and as we see Airflow is used now in multiple cases > >> > where > >> > > there is no need to process data from an interval and wait until > that > >> > data > >> > > is ready. > >> > > But indeed some more tests would be great - especially for edge > cases. > >> > > Changig mid-air is one but I think there should be test about > Daylight > >> > > Saving Time changing. > >> > > There are some tests for DST so they just need to be extended to > cover > >> > > those two different cases. > >> > > > >> > > > >> > > J. > >> > > > >> > > On Fri, Aug 23, 2019 at 7:37 AM Kaxil Naik <kaxiln...@gmail.com> > >> wrote: > >> > > > >> > > > Happy for this feature to merged > >> > > > > >> > > > On Fri, Aug 23, 2019, 11:49 Ash Berlin-Taylor <a...@apache.org> > >> wrote: > >> > > > > >> > > > > This has come up a few times before, someone has now opened a PR > >> that > >> > > > > makes this a global+per-dag setting: > >> > > > > https://github.com/apache/airflow/pull/5787 and it also > includes > >> > docs > >> > > > > that I think does a good job of illustrating the two modes. > >> > > > > > >> > > > > Does anyone object to this being merged? If no one says anything > >> by > >> > > > midday > >> > > > > on Tuesday I will take that as assent and will merge it. > >> > > > > > >> > > > > The docs from the PR included below. > >> > > > > > >> > > > > Thanks, > >> > > > > Ash > >> > > > > > >> > > > > Scheduled Time vs Execution Time > >> > > > > '''''''''''''''''''''''''''''''' > >> > > > > > >> > > > > A DAG with a ``schedule_interval`` will execute once per > >> interval. By > >> > > > > default, the execution of a DAG will occur at the **end** of the > >> > > > > schedule interval. > >> > > > > > >> > > > > A few examples: > >> > > > > > >> > > > > - A DAG with ``schedule_interval='@hourly'``: The DAG run that > >> > > processes > >> > > > > 2019-08-16 17:00 will start running just after 2019-08-16 > >> 17:59:59, > >> > > > > i.e. once that hour is over. > >> > > > > - A DAG with ``schedule_interval='@daily'``: The DAG run that > >> > processes > >> > > > > 2019-08-16 will start running shortly after 2019-08-17 00:00. > >> > > > > > >> > > > > The reasoning behind this execution vs scheduling behaviour is > >> that > >> > > > > data for the interval to be processed won't be fully available > >> until > >> > > > > the interval has elapsed. > >> > > > > > >> > > > > In cases where you wish the DAG to be executed at the **start** > of > >> > the > >> > > > > interval, specify ``schedule_at_interval_end=False``, either in > >> > > > > ``airflow.cfg``, or on a per-DAG basis. > >> > > > > >> > > > >> > > > >> > > -- > >> > > > >> > > Jarek Potiuk > >> > > Polidea <https://www.polidea.com/> | Principal Software Engineer > >> > > > >> > > M: +48 660 796 129 <+48660796129> > >> > > [image: Polidea] <https://www.polidea.com/> > >> > > > >> > > >> > >> > >> -- > >> > >> Jarek Potiuk > >> Polidea <https://www.polidea.com/> | Principal Software Engineer > >> > >> M: +48 660 796 129 <+48660796129> > >> [image: Polidea] <https://www.polidea.com/> > >> > > >
