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From <>
Subject Re: Simple DAG Structure
Date Mon, 23 Jul 2018 13:33:48 GMT
Carl - 

   Thanks, that definitely works, but it's non-ideal. If I had 100s of jobs running throughout
the day, a TimeSensor task (process) gets created for each task at midnight even though a
task may not be required to run for a very long time (e.g. a whole bunch of tasks need to
run @ 20:00. All of their time sensors are kicked off at 00:00). Worse still, if I used a
LocalExcecutor with a pool size of 10, some jobs that need to run early may not even get scheduled
in favor of time sensors for tasks later in the day which only perform a sleep operation.

   Is there another way to do this? If not, is there at least another way around the LocalExecutor


On 2018/07/23 08:23:45, Carl Johan Gustavsson <> wrote: 
> Hi Ram,
> You can have a single DAG scheduled to 10am, which starts A and then use a TimeSensor
set to 11 am that B depends on  and then have C depend on A and B.
> Something like:
> a = BashOperator(‘a’, …)
> delay_b = TimeSensor(‘delay_b’, target_time=time(11, 0, 0), …)
> b = BashOperator(‘b’, …)
> b.set_upstream(delay_b)
> c = BashOperator(‘c’, …)
> c.set_upstream(a)
> c.set_upstream(b)
> / Carl Johan
> On 23 July 2018 at 02:18:00, (
> Hi -  
> I have recently started using Airflow version 1.9.0 and am having some difficulty setting
up a very simple DAG. I have three tasks A, B and C. I'd like A to run every day at 10am and
B at 11am. C depends on BOTH A and B running successfully.  
> Initially, I decided to create one DAG, add all three tasks to it and set C as downstream
to A and B. I then set the schedule_interval of the DAG to @daily. But this meant I couldn't
run A and B at 10am and 11am respectively since the they are PythonOperators and tasks dont
support schedule_interval (or, at least, it's deprecated syntax and gets ignored).  
> I scratched that idea and then created A and B as DAGs, specified the schedule interval
as per the cron syntax: '00 10 * * *' for A and '00 11 * * *' for B. But now when I set C
as a downstream of A and B, it complains that C can't belong to two different dags.  
> How do I accomplish such a simple dependency structure?  
> Ram.  

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