Open Stack

Hi,

I'm a beginner in OpenStack development.

I would like to try modifying by adding a property to the 'Instances'
database table. But I didn't find description in the documentation of
the data model mechanism and how to extend the database.
https://docs.openstack.org/nova/latest/

Now, I know that it involves versined object model and alembic.

My question is:
What is the process of adding a column to a table in the database?

Could someone show me the process of modifying a database table or
recommend me the relevant documentation

Best wishes,
Han