SQL Server Migration Block on initdb

[Chad Henderson <ch...@gritlogic.com>]

Good afternoon,

I ran into an issue while trying to deploy Airflow using a MS-SQL 2012
backend. Two alembic migrations were causing the issue:
e3a246e0dc1_current_schema.py
and 1507a7289a2f_create_is_encrypted.py.

It seems that by using separate engine instances, that the inspector object
and the op object were causing each others' queries to block.

Once I switched the engine that the inspector was using from
settings.engine to op.get_bind() the migrations completed successfully.

I couldn't find any issues surrounding this problem in Jira to reference
along with a PR, and it doesn't seem that just anyone can create an issue,
but I'll submit my fix as a PR if anyone thinks it would be of value. I'm
just not sure how to proceed.

Thanks,

Chad Henderson