[GitHub] [airflow] SamWheating commented on a change in pull request #20349: Fix Scheduler crash when executing task instances of missing DAG

[GitBox <gi...@apache.org>]

SamWheating commented on a change in pull request #20349:
URL: https://github.com/apache/airflow/pull/20349#discussion_r783317103



##########
File path: airflow/jobs/scheduler_job.py
##########
@@ -403,6 +403,15 @@ def _executable_task_instances_to_queued(self, max_tis: int, session: Session =
                     # Many dags don't have a task_concurrency, so where we can avoid loading the full
                     # serialized DAG the better.
                     serialized_dag = self.dagbag.get_dag(dag_id, session=session)
+                    # If the dag is missing, fail the task and continue to the next task.
+                    if not serialized_dag:
+                        self.log.error(
+                            "DAG '%s' for task instance %s not found in serialized_dag table",
+                            dag_id,
+                            task_instance,
+                        )
+                        task_instance.set_state(State.FAILED, session=session)

Review comment:
       Is it possible to set the entire DAG to `FAILED` here? Depending on the trigger rules, there could be downstream tasks which still attempt to execute, which will also fail due to a missing DAG. 




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