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From הילה ויזן <>
Subject Re: problem to update 'start_date' of DAG
Date Wed, 10 Aug 2016 04:24:59 GMT
Hi Maxime,

Thanks for the clarifications.
I've already read this page while trying to find a solution to my problem.

But I still have the question - is there any way to discard the previous
definitions? (for example the 'start_date' of a DAG)


On Wed, Aug 10, 2016 at 1:37 AM, Maxime Beauchemin <> wrote:

> From
> *What’s the deal with ``start_date``?*
> start_date is partly legacy from the pre-DagRun era, but it is still
> relevant in many ways. When creating a new DAG, you probably want to set a
> global start_date for your tasks usingdefault_args. The first DagRun to be
> created will be based on the min(start_date) for all your task. From that
> point on, the scheduler creates new DagRuns based on your
> schedule_interval and
> the corresponding task instances run as your dependencies are met. When
> introducing new tasks to your DAG, you need to pay special attention to
> start_date, and may want to reactivate inactive DagRuns to get the new task
> to get onboarded properly.
> We recommend against using dynamic values as start_date, especially
> as it can be quite confusing. The task is triggered once the
> period closes, and in theory an @hourly DAG would never get to an hour
> after now as now() moves along.
> Previously we also recommended using rounded start_date in relation to your
> schedule_interval. This meant an @hourly would be at 00:00 minutes:seconds,
> a @daily job at midnight, a @monthlyjob on the first of the month. This is
> no longer required. Airflow will not auto align the start_dateand the
> schedule_interval, by using the start_date as the moment to start looking.
> You can use any sensor or a TimeDeltaSensor to delay the execution of tasks
> within the schedule interval. While schedule_interval does allow specifying
> a datetime.timedelta object, we recommend using the macros or cron
> expressions instead, as it enforces this idea of rounded schedules.
> When using depends_on_past=True it’s important to pay special attention to
> start_date as the past dependency is not enforced only on the specific
> schedule of the start_date specified for the task. It’ also important to
> watch DagRun activity status in time when introducing new
> depends_on_past=True, unless you are planning on running a backfill for the
> new task(s).
> Also important to note is that the tasks start_date, in the context of a
> backfill CLI command, get overridden by the backfill’s command start_date.
> This allows for a backfill on tasks that havedepends_on_past=True to
> actually start, if it wasn’t the case, the backfill just wouldn’t start.
> On Tue, Aug 9, 2016 at 7:44 AM, הילה ויזן <> wrote:
> > Hi,
> >
> > We're experiencing a strange problem with the start_date configuration in
> > Airflow.
> >
> > When we first ran the DAGs, we defined the start_date as
> '',
> > which at the time was 01/08/2016. This worked fine. A week afterwards, we
> > changed the DAGs to a specific newer date - 08/08/2016, and reset all of
> > the tasks. After resetting the Airflow and all of the DAGs *we are still
> > seeing the tasks running from original date (01/08)*. Why is this
> > happening?
> >
> > We don't understand why the tasks are still using the old date. Is there
> a
> > cache/DB/persistent file that the DAG reads on startup that overrides our
> > definition? Is it maybe Celery? We really would appreciate your input
> > because we are totally stuck.
> >
> > We use airflow version with postgress as the backend DB.
> > In addition, we run in CeleryExecutor mode with rabbitMQ as Celery
> backend.
> >
> > Thank you,
> > Hila
> >

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