Thank you for explaining those details and pointing me in the right direction about the proper way to solve the problem in oslo.db.

We still have to support python 3.6, so for now we will still need to do something different (in nova) to handle this (clear our cache of oslo.db _TransactionContextManager during oslo.service start(), is what I have proposed).

For those running python 3.7 and newer, I will try to fix the situation more generally in oslo.db with os.register_at_fork() using the examples you gave.

Thank you again for your help, I have learned a lot.