It won't take effect when updating the start_date in the default_args

[htgeis]

Apache Airflow version: v1.10.14

Environment:

• Cloud provider or hardware configuration:
• OS (e.g. from /etc/os-release): Ubuntu 16.04.3 LTS
• Kernel (e.g. uname -a): Linux aor-k8s-ci-test-01 4.4.0-1111-aws How do you use hooks? #123-Ubuntu SMP Sat Jul 4 02:03:15 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
• Install tools: pip
• Others:

What happened:
it won't take effect when updating the start_date in the default_args.
e.g. a daily job like this
default_args = { 'owner': 'airflow', 'depends_on_past': False, 'start_date': timezone.datetime(2020, 5, 1) } dag = DAG(dag_id, schedule_interval=timedelta(days=1), max_active_runs=5, catchup=True, default_args=default_args)
It would schedule the first dag run of "2020/05/01" and if we updated start_date above to "2020/10/01", the next dag it would schedule is "2020/05/02" instead of "2020/10/01", which means it would not take effect.

What you expected to happen:

when start_date has changed, the execution_time of the next dag run should not be early than it.

How to reproduce it:

    def test_dag_when_start_date_changes(self):
        """
        Test to check that a DAG could schedule reasonable when start_date defined in
        default_args has changed
        """

        def setup_dag(dag_id, schedule_interval, start_date, catchup):
            default_args = {
                'owner': 'airflow',
                'depends_on_past': False,
                'start_date': start_date
            }
            dag = DAG(dag_id,
                      schedule_interval=schedule_interval,
                      max_active_runs=5,
                      catchup=catchup,
                      default_args=default_args)

            t1 = DummyOperator(task_id='t1', dag=dag)
            t2 = DummyOperator(task_id='t2', dag=dag)
            t2.set_upstream(t1)
            t3 = DummyOperator(task_id='t3', dag=dag)
            t3.set_upstream(t2)

            session = settings.Session()
            orm_dag = DagModel(dag_id=dag.dag_id)
            session.merge(orm_dag)
            session.commit()
            session.close()

            return dag

        now = timezone.utcnow()
        half_an_hour_ago = now - datetime.timedelta(minutes=30)
        next_month = now + datetime.timedelta(days=30)

        scheduler = SchedulerJob()

        dag1 = setup_dag(dag_id='dag_with_catchup',
                         schedule_interval=timedelta(days=1),
                         start_date=timezone.datetime(2020, 5, 1),
                         catchup=True)
        dr = scheduler.create_dag_run(dag1)
        self.assertIsNotNone(dr)
        self.assertEqual(dr.execution_date, timezone.datetime(2020, 5, 1))
        dr = scheduler.create_dag_run(dag1)
        self.assertIsNotNone(dr)
        self.assertEqual(dr.execution_date, timezone.datetime(2020, 5, 2))
        # update start_date
        dag1 = setup_dag(dag_id='dag_with_catchup',
                         schedule_interval=timedelta(days=1),
                         start_date=timezone.datetime(2020, 10, 1),
                         catchup=True)
        dr = scheduler.create_dag_run(dag1)
        self.assertIsNotNone(dr)
        self.assertEqual(dr.execution_date, timezone.datetime(2020, 10, 1))
        dr = scheduler.create_dag_run(dag1)
        self.assertIsNotNone(dr)
        self.assertEqual(dr.execution_date, timezone.datetime(2020, 10, 2))

        dag2 = setup_dag(dag_id='dag_with_catchup_cron',
                         schedule_interval='0 0 * * *',
                         start_date=timezone.datetime(2020, 5, 1),
                         catchup=True)
        dr = scheduler.create_dag_run(dag2)
        self.assertIsNotNone(dr)
        self.assertEqual(dr.execution_date, timezone.datetime(2020, 5, 1))
        dr = scheduler.create_dag_run(dag2)
        self.assertIsNotNone(dr)
        self.assertEqual(dr.execution_date, timezone.datetime(2020, 5, 2))
        # update start_date
        dag2 = setup_dag(dag_id='dag_with_catchup_cron',
                         schedule_interval='0 0 * * *',
                         start_date=timezone.datetime(2020, 10, 1),
                         catchup=True)
        dr = scheduler.create_dag_run(dag2)
        self.assertIsNotNone(dr)
        self.assertEqual(dr.execution_date, timezone.datetime(2020, 10, 1))
        dr = scheduler.create_dag_run(dag2)
        self.assertIsNotNone(dr)
        self.assertEqual(dr.execution_date, timezone.datetime(2020, 10, 2))

        dag3 = setup_dag(dag_id='dag_without_catchup_with_future_day',
                         schedule_interval='*/10 * * * *',
                         start_date=timezone.datetime(2020, 5, 1),
                         catchup=False)
        dr = scheduler.create_dag_run(dag3)
        self.assertIsNotNone(dr)
        self.assertGreater(dr.execution_date, half_an_hour_ago)
        # update start_date
        dag3 = setup_dag(dag_id='dag_without_catchup_with_future_day',
                         schedule_interval='*/10 * * * *',
                         start_date=next_month,
                         catchup=False)
        dr = scheduler.create_dag_run(dag3)
        self.assertIsNone(dr)

        dag4 = setup_dag(dag_id='dag_with_catchup_once',
                         schedule_interval='@once',
                         start_date=timezone.datetime(2020, 5, 1),
                         catchup=True)
        dr = scheduler.create_dag_run(dag4)
        self.assertIsNotNone(dr)
        self.assertEqual(dr.execution_date, timezone.datetime(2020, 5, 1))
        # update start_date
        dag4 = setup_dag(dag_id='dag_with_catchup_once',
                         schedule_interval='@once',
                         start_date=timezone.datetime(2020, 10, 1),
                         catchup=True)
        dr = scheduler.create_dag_run(dag4)
        self.assertIsNone(dr)

Anything else we need to know:

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[ashb]

the next dag it would schedule is "2020/05/02" instead of "2020/10/01", which means it would not take effect.

Am I right in thinking that it would schedule those dags, bug not actually run any of the tasks in those dag runs currently?

[htgeis]

the next dag it would schedule is "2020/05/02" instead of "2020/10/01", which means it would not take effect.

Am I right in thinking that it would schedule those dags, bug not actually run any of the tasks in those dag runs currently?

yeah, but it doesn't make much sense to create these dag runs with no tasks runnable. We have many users defined the start_date in the default_args and they have some requirements to change the start_date. Sometimes, it's a larger time interval between these two dates, thus it would waste time to waiting for these empty dag runs created and it's also not friendly to show dag runs in web ui as they would see a larger number of empty dags runs.