apache airflow scheduler not scheduling jobs

Question

I'm working with apache airflow 1.8.0.

Here is output when I backfill the job.

[2017-04-13 09:42:55,857] {models.py:1126} INFO - Dependencies all met for <TaskInstance: example_bash_operator.runme_1 2017-04-13 13:43:00     [scheduled]>
[2017-04-13 09:42:55,857] {models.py:1126} INFO - Dependencies all met for <TaskInstance: example_bash_operator.runme_1 2017-04-13 13:43:00 [scheduled]>
[2017-04-13 09:42:55,857] {models.py:1126} INFO - Dependencies all met for <TaskInstance: example_bash_operator.runme_2 2017-04-13 13:45:00 [scheduled]>
[2017-04-13 09:42:55,858] {models.py:1126} INFO - Dependencies all met for <TaskInstance: example_bash_operator.runme_2 2017-04-13 13:45:00 [scheduled]>
[2017-04-13 09:42:55,858] {models.py:1126} INFO - Dependencies all met for <TaskInstance: example_bash_operator.runme_2 2017-04-13 13:43:00 [scheduled]>
[2017-04-13 09:42:55,858] {models.py:1126} INFO - Dependencies all met for <TaskInstance: example_bash_operator.runme_2 2017-04-13 13:43:00 [scheduled]>
[2017-04-13 09:42:55,858] {models.py:1126} INFO - Dependencies all met for <TaskInstance: example_bash_operator.also_run_this 2017-04-13 13:44:00 [scheduled]>
[2017-04-13 09:42:55,858] {models.py:1126} INFO - Dependencies all met for <TaskInstance: example_bash_operator.also_run_this 2017-04-13 13:44:00 [scheduled]>
[2017-04-13 09:42:55,864] {models.py:1120} INFO - Dependencies not met for <TaskInstance: example_bash_operator.run_after_loop 2017-04-13 13:44:00 [scheduled]>, dependency 'Trigger Rule' FAILED: Task's trigger rule 'all_success' requires all upstream tasks to have succeeded, but found 3 non-success(es). upstream_tasks_state={'skipped': Decimal('0'), 'successes': Decimal('0'), 'done': 0, 'upstream_failed': Decimal('0'), 'failed': Decimal('0')}, upstream_task_ids=['runme_0', 'runme_1', 'runme_2']

when I try to schedule any DAG it throws error.

Traceback (most recent call last):
  File "/anaconda3/bin/airflow", line 28, in <module>
    args.func(args)
  File "/anaconda3/lib/python3.5/site-packages/airflow/bin/cli.py", line 167, in backfill
    pool=args.pool)
  File "/anaconda3/lib/python3.5/site-packages/airflow/models.py", line 3330, in run
    job.run()
  File "/anaconda3/lib/python3.5/site-packages/airflow/jobs.py", line 200, in run
    self._execute()
  File "/anaconda3/lib/python3.5/site-packages/airflow/jobs.py", line 2021, in _execute
    raise AirflowException(err)
airflow.exceptions.AirflowException: ---------------------------------------------------

Here is output about tasks.

BackfillJob is deadlocked. These tasks have succeeded:
set()
 These tasks have started:
{}
 These tasks have failed:
set()
 These tasks are skipped:
set()
 These tasks are deadlocked:
{<TaskInstance: example_bash_operator.runme_0 2017-04-13 13:44:00 [scheduled]>, <TaskInstance: example_bash_operator.runme_1 2017-04-13 13:44:00 [scheduled]>, <TaskInstance: example_bash_operator.runme_0 2017-04-13 13:46:00 [scheduled]>, <TaskInstance: example_bash_operator.runme_2 2017-04-13 13:44:00 [scheduled]>, <TaskInstance: example_bash_operator.also_run_this 2017-04-13 13:46:00 [scheduled]>, <TaskInstance: example_bash_operator.runme_0 2017-04-13 13:45:00 [scheduled]>, <TaskInstance: example_bash_operator.run_this_last 2017-04-13 13:46:00 [scheduled]>, <TaskInstance: example_bash_operator.runme_1 2017-04-13 13:46:00 [scheduled]>, <TaskInstance: example_bash_operator.runme_2 2017-04-13 13:46:00 [scheduled]>, <TaskInstance: example_bash_operator.run_after_loop 2017-04-13 13:46:00 [scheduled]>, <TaskInstance: example_bash_operator.also_run_this 2017-04-13 13:43:00 [scheduled]>, <TaskInstance: example_bash_operator.run_after_loop 2017-04-13 13:43:00 [scheduled]>, <TaskInstance: example_bash_operator.run_this_last 2017-04-13 13:45:00 [scheduled]>, <TaskInstance: example_bash_operator.also_run_this 2017-04-13 13:45:00 [scheduled]>, <TaskInstance: example_bash_operator.run_this_last 2017-04-13 13:43:00 [scheduled]>, <TaskInstance: example_bash_operator.runme_0 2017-04-13 13:43:00 [scheduled]>, <TaskInstance: example_bash_operator.runme_1 2017-04-13 13:45:00 [scheduled]>, <TaskInstance: example_bash_operator.run_after_loop 2017-04-13 13:45:00 [scheduled]>, <TaskInstance: example_bash_operator.runme_1 2017-04-13 13:43:00 [scheduled]>, <TaskInstance: example_bash_operator.runme_2 2017-04-13 13:45:00 [scheduled]>, <TaskInstance: example_bash_operator.runme_2 2017-04-13 13:43:00 [scheduled]>, <TaskInstance: example_bash_operator.also_run_this 2017-04-13 13:44:00 [scheduled]>, <TaskInstance: example_bash_operator.run_after_loop 2017-04-13 13:44:00 [scheduled]>, <TaskInstance: example_bash_operator.run_this_last 2017-04-13 13:44:00 [scheduled]>}

tested with python 2.7 and python 3.5

used SequentialExecutor and LocalExecutor

PS. if I backfill the DAG at current time, it executes for once, and then throws the above error for all the scheduled tasks.

Answer 1

Your airflow instance is in deadlock state. The task which has failed is not allowing future runs of the task.

Airflow launches each task in each dag run as a new process and when the task falters and this is not handled deadlock situation arises

To resolve this situation you can do one of the following:

1. use airflow clear <<dag_id>> This will resolve the deadlock and allow future runs of the DAG/task
2. If above does not solve the issue, you would need to use airflow resetdb This would clear the airflow database and hence resolve the issue

In future,

• try and use execution_timeout=timedelta(minutes=2) set some timeout so that you have explicit control on operator
• Also, do provide a on_failure_callback=handle_failure which would cleanly exist the operator on failure

Hope this helps,

Cheers!