Comment 1 for bug 1771810

This seems like either something that should be a part of https://blueprints.launchpad.net/nova/+spec/handling-down-cell or https://blueprints.launchpad.net/nova/+spec/count-quota-usage-from-placement.

Even if we pre-determined which cells the project has instances in, if any of those cells are down then we're still not getting an accurate usage count if we're using the cell database. To pre-determine which cells a project has instances in, I think we could do that via the instance_mappings records in the nova_api database, maybe similar to how listing instances was modified with this change:

https://review.openstack.org/#/c/509003/

The instance_mappings table doesn't have a user_id column so any quota we would need to count that involves a user_id would not work here though. This bug isn't specific about which quota is being calculated and when (server create or just when hitting the limits API?).