Comment 2 for bug 1835037

Looks like an issue when executing 'nova-manager db online_data_migrations'.

Can you share package version currently installed:
$ dpkg -s nova-common

Also sharing logs of nova-manage located under /var/log/nova may help.

If you have not configured your env in debug, please consider using:
$ juju config nova-cloud-controller debug=true

Then you could try to ru-run locally:
$ nova-manager db online_data_migrations

Thanks,
s.