jedcunningham commented on issue #18939:
URL: https://github.com/apache/airflow/issues/18939#issuecomment-953395944
I was able to reproduce this. The following traceback is the original
failure:
```
File
"/Users/jedc/github/airflow/airflow/migrations/versions/7b2661a43ba3_taskinstance_keyed_to_dagrun.py",
line 322, in upgrade
ondelete=ondelete,
...
sqlalchemy.exc.OperationalError: (MySQLdb._exceptions.OperationalError)
(3780, "Referencing column 'dag_id' and referenced column 'dag_id' in foreign
key constraint 'task_reschedule_ti_fkey' are incompatible.")
[SQL: ALTER TABLE task_reschedule ADD CONSTRAINT task_reschedule_ti_fkey
FOREIGN KEY(dag_id, task_id, run_id) REFERENCES task_instance (dag_id, task_id,
run_id) ON DELETE CASCADE]
```
Which is this section:
https://github.com/apache/airflow/blob/20847fdbf8ecd3be394d24d47ce151c26d018ea1/airflow/migrations/versions/7b2661a43ba3_taskinstance_keyed_to_dagrun.py#L303-L310
This fails because the column in `task_instance` and differ:
```
# task_instance
`dag_id` varchar(250) CHARACTER SET utf8 COLLATE utf8_bin NOT NULL,
# task_reschedule
`dag_id` varchar(250) NOT NULL,
```
The traceback in the description then happens on subsequent `airflow db
upgrade` runs.
The root cause is incorrect encoding/collation settings. If I follow the
documentation for using a [MySQL database with
Airflow](https://airflow.apache.org/docs/apache-airflow/stable/howto/set-up-database.html#setting-up-a-mysql-database),
everything is happy. If I use the defaults we run into this.
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