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From siddharth anand <san...@apache.org>
Subject Re: scheduler questions
Date Thu, 13 Oct 2016 17:34:17 GMT
Yes! It does work with Depends_on_past=True.
-s

On Thu, Oct 13, 2016 at 10:28 AM, Boris Tyukin <boris@boristyukin.com>
wrote:

> thanks so much, Sid! just a follow up question on "Only_Run_Latest" - will
> it work with depend_on_past = True? or it will assume that DAG is used
> False?
>
> On Thu, Oct 13, 2016 at 1:11 PM, siddharth anand <sanand@apache.org>
> wrote:
>
> > Boris,
> >
> > *Question 1*
> > Only_Run_Latest is in master -
> > https://github.com/apache/incubator-airflow/commit/
> > edf033be65b575f44aa221d5d0ec9ecb6b32c67a.
> > That will solve your problem.
> >
> > Releases come out one a quarter sometimes once every 2 quarters, so I
> would
> > recommend that you run off master or off your own fork.
> >
> > You could also achieve this yourself with the following code snippet. It
> > uses a ShortCircuitOperator that will skip downstream tasks if the DagRun
> > being executed is not the current one. It will work for any schedule. The
> > code below has essentially been implemented in the LatestOnlyOperator
> above
> > for convenience.
> >
> > def skip_to_current_job(ds, **kwargs):
> >
> >     now = datetime.now()
> >
> >     left_window = kwargs['dag'].following_schedule(kwargs['execution_
> > date'])
> >
> >     right_window = kwargs['dag'].following_schedule(left_window)
> >
> >     logging.info(('Left Window {}, Now {}, Right Window {}'
> > ).format(left_window,now,right_window))
> >
> >     if not now <= right_window:
> >
> >         logging.info('Not latest execution, skipping downstream.')
> >
> >         return False
> >
> >     return True
> >
> >
> > t0 = ShortCircuitOperator(
> >
> >   task_id         = 'short_circuit_if_not_current,
> >
> >   provide_context = True,
> >
> >   python_callable = skip_to_current_job,
> >
> >   dag             = dag
> >
> > )
> >
> >
> > -s
> >
> >
> > On Thu, Oct 13, 2016 at 7:46 AM, Boris Tyukin <boris@boristyukin.com>
> > wrote:
> >
> > > Hello all and thanks for such an amazing project! I have been
> evaluating
> > > Airflow and spent a few days reading about it and playing with it and I
> > > have a few questions that I struggle to understand.
> > >
> > > Let's say I have a simple DAG that runs once a day and it is doing a
> full
> > > reload of tables from the source database so the process is not
> > > incremental.
> > >
> > > Let's consider this scenario:
> > >
> > > Day 1 - OK
> > >
> > > Day 2 - airflow scheduler or server with airflow is down for some
> reason
> > > ((or
> > > DAG is paused)
> > >
> > > Day 3 - still down(or DAG is paused)
> > >
> > > Day 4 - server is up and now needs to run missing jobs.
> > >
> > >
> > > How can I make airflow to run only Day 4 job and not backfill Day 2 and
> > 3?
> > >
> > >
> > > I tried to do depend_on_past = True but it does not seem to do this
> > trick.
> > >
> > >
> > > I also found in a roadmap doc this but seems it is not made to the
> > release
> > > yet:
> > >
> > >
> > >  Only Run Latest - Champion : Sid
> > >
> > > • For cases where we need to only run the latest in a series of task
> > > instance runs and mark the others as skipped. For example, we may have
> > job
> > > to execute a DB snapshot every day. If the DAG is paused for 5 days and
> > > then unpaused, we don’t want to run all 5, just the latest. With this
> > > feature, we will provide “cron” functionality for task scheduling that
> is
> > > not related to ETL
> > >
> > >
> > > My second question, what if I have another DAG that does incremental
> > loads
> > > from a source table:
> > >
> > >
> > > Day 1 - OK, loaded new/changed data for previous day
> > >
> > > Day 2 - source system is down (or DAG is paused), Airflow DagRun failed
> > >
> > > Day 3 - source system is down (or DAG is paused), Airflow DagRun failed
> > >
> > > Day 4 - source system is up, Airflow Dagrun succeeded
> > >
> > >
> > > My problem (unless I am missing something), Airflow on Day 4 would use
> > > execution time from Day 3, so the interval for incremental load would
> be
> > > since the last run (which was Failed). My hope it would use the last
> > > _successful_ run so on Day 4 it would go back to Day 1. Is it possible
> to
> > > achieve this?
> > >
> > > I am aware of a manual backfill command via CLI but I am not sure I
> want
> > to
> > > use due to all the issues and inconsistencies I've read about it.
> > >
> > > Thanks!
> > >
> >
>

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