potiuk commented on code in PR #35825:
URL: https://github.com/apache/airflow/pull/35825#discussion_r1404115850
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docs/apache-airflow/core-concepts/tasks.rst:
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@@ -243,9 +243,103 @@ Zombie/Undead Tasks
No system runs perfectly, and task instances are expected to die once in a
while. Airflow detects two kinds of task/process mismatch:
-* *Zombie tasks* are tasks that are supposed to be running but suddenly died
(e.g. their process was killed, or the machine died). Airflow will find these
periodically, clean them up, and either fail or retry the task depending on its
settings.
+* *Zombie tasks* are ``TaskInstances`` stuck in a ``running`` state despite
their associated jobs being inactive
+ (e.g. their process didn't send a recent heartbeat as it got killed, or the
machine died). Airflow will find these
+ periodically, clean them up, and either fail or retry the task depending on
its settings.
+
+* *Undead tasks* are tasks that are *not* supposed to be running but are,
often caused when you manually edit Task
+ Instances via the UI. Airflow will find them periodically and terminate them.
+
+
+Below is the code snippet from the Airflow scheduler that runs periodically to
detect zombie/undead tasks.
+
+.. exampleinclude:: /../../airflow/jobs/scheduler_job_runner.py
+ :language: python
+ :start-after: [START find_zombies]
+ :end-before: [END find_zombies]
+
+
+The explanation of the criteria used in the above snippet to detect zombie
tasks is as below:
+
+1. **Task Instance State**
+
+ Only task instances in the RUNNING state are considered potential zombies.
+
+.. code-block::
+
+ .where(TI.state == TaskInstanceState.RUNNING)
Review Comment:
I think it's better to explain these it in SQL terms - translating this to
WHERE statement would be more widely understood by the users
Not many of our users know ORM/sqlalchemy
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