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Hi folks,

I am working on nova-network in Havana. I have a very unique use case where I need to add duplicate VLANs in nova-network. I am trying to add multiple networks in nova-network with same VLAN ID. The reason is as follows:

The cluster that I have has an L3 backplane. We have been given a limitation that, per rack, we have a few networks with unique VLAN tags, and the VLAN tags repeat in every rack. So now, when I add networks in nova-network, I need to add these networks in same VLAN. 

nova-network currently has a unique constraint on ("vlan", "deleted"). So to allow for duplicate VLANs in  the DB, I am removing that unique constraint. I am modifying the migrate scripts to make sure that UC doesn't apply again on db_sync.  I am also modifying the unit tests to reverse their sense (make sure that duplicate VLANs are allowed)

After making these changes, I have verified following scenarios:
1. Add networks with duplicate VLANs
2. Update networks with duplicate VLANs
3. db_sync doesn't revert back the constraint.
4. VM comes up properly and I can ping it. 

Since this is a DB schema change, I am a bit skeptical about it, and hence, looking for expert advice.

1. How risky is it to make DB schema change?
2. I know that I have to look out for any new migration scripts that touch that UC/Index. Anything else that I need to worry about w.r.t migration scripts?
3. Any more scenarios I should be testing?

Thank you in advance!
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