I am *strongly* in favor of using the 2.0 update to break compat here, because this is a very confusing feature to most new users of Airflow, but also will break a _lot_ of DAGs. I feel like if we don't change this in 2.0 we probably won't for any 2.x either, which would be a shame.
On Wed, Sep 25, 2019 at 8:33 PM Kaxil Naik <kaxiln...@gmail.com> wrote: > I agree with Dan to change the default execution at start of the interval. > > How about adding this for 2.0 ?? > > Don't want to keep delaying this if we have a consensus already. > > Regards, > Kaxil > > > On Fri, Aug 23, 2019, 15:39 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/> > > >> > > > > > >
