Comment 10 for bug 1566520

Akihiro, that's correct. That RFE requires three pieces: 1) newer neutron-server being aware of older schema; 2) no data migration in alembic (moving it to the neutron-server process thru objects); 3) postpone contract schema changes to when all servers are upgraded. The complete process may span more cycles than just two because the new server will still access the old schema even after all services are upgraded. So you can drop the old schema in a next cycle only AFTER you started to roll in the update to database.