SamWheating commented on issue #15559:
URL: https://github.com/apache/airflow/issues/15559#issuecomment-832942105


   Just following up to confirm that switching our database's isolation level 
from `REPEATABLE READ` to `READ COMMITTED` fixed the original issue in our case 
and allowed us to run multiple schedulers without issue. 
   
   Its worth noting that the default for Postgres is `READ COMMITTED`, so 
Postgres users likely did not encounter this issue. 
   
   @trollhe, could you confirm the following?
   1) You're also using MySQL 8 with `REPEATABLE READ` isolation level. 
   2) Changing the isolation level to `READ COMMITTED` fixes the original 
issue. 
   
   ### Fixing this Issue
   
   I think there's a few possible ways to "fix" this issue. 
   
   1) Add a note in the docs that reminds users to configure the correct 
isolation level when using MySQL 8
   1) Add a check in 
[`create_engine_args()`](https://github.com/apache/airflow/blob/d295e708d982082caa68b08ab29c8aa4bf67dce5/airflow/settings.py#L240)
 to add `isolation_level=READ COMMITTED` when MySQL is being used. 
   1) Add a config option to provide additional engine args, or to set the 
isolation level.
   
   Any thoughts on the preferred fix? Feel free to assign this to me and I can 
implement one of these fixes this week.  


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