Example:
DAG structure:
```
default_args = {
    'owner': 'dimon',
    'depends_on_past': False,
    'start_date': datetime(2021, 1, 10)
}

dag = DAG(
    'dummy-dag',
    schedule_interval='21 2 * * *',
    catchup=False,
    default_args=default_args
)

DagContext.push_context_managed_dag(dag)
task1 = BashOperator(task_id='task1', bash_command='echo 1')
task2 = BashOperator(task_id='task2', bash_command='echo 2')
task2 << task1
task3 = BashOperator(task_id='task3', bash_command='echo 3')
```

Let’s say you’ve missed the button and typed `--task-regex task4`.
When the backfill starts, firstly it will create a new empty DagRun and puts it in DB. Then the backfill job will go and try to find tasks that match the regex you’ve entered, will not find any obviously and will be stuck in the “running” state together with newly created DagRun forever.

airflow/cli/commands/dag_command.py
"""Unpauses a DAG"""
    set_is_paused(False, args)
def set_is_paused(is_paused, args):
    """Sets is_paused for DAG by a given dag_id"""
    dag = DagModel.get_dagmodel(args.dag_id)
    if not dag:
        raise SystemExit(f"DAG: {args.dag_id} does not exist in 'dag' table")
    dag.set_is_paused(is_paused=is_paused)
    print(f"Dag: {args.dag_id}, paused: {is_paused}")
def dag_show(args):
    """Displays DAG or saves it's graphic representation to the file"""
    dag = get_dag(args.subdir, args.dag_id)
    dot = render_dag(dag)
    filename = args.save
    imgcat = args.imgcat
    if filename and imgcat:
        raise SystemExit(
            "Option --save and --imgcat are mutually exclusive. "
            "Please remove one option to execute the command.",
        )
    elif filename:
        _save_dot_to_file(dot, filename)
    elif imgcat:
        _display_dot_via_imgcat(dot)
    else:
        print(dot.source)
def _display_dot_via_imgcat(dot: Dot):