Comment 4 for bug 1799892

There is an online data migration:

https://review.openstack.org/#/c/377138/62/nova/objects/resource_provider.py@917

But it's only when listing/showing resource providers. The allocation candidates code must be getting the providers and relying on the root_provider_id using sqla model objects rather than the versioned objects that do the online data migration.

This is where something like "placement-manage db online_data_migrations" would be useful.