[openstack-dev] [Glance] Block subtractive schema changes

Dulko, Michal michal.dulko at intel.com
Thu Mar 24 11:36:28 UTC 2016

On Thu, 2016-03-24 at 10:45 +0000, stuart.mclaren at hp.com wrote:
> I think this makes sense (helps us spot things which could impact upgrade).
> >Hi Glance Team,
> >
> >I have registered a blueprint [1] for blocking subtractive schema changes.
> >Cinder and Nova are already supporting blocking of subtractive schema operations. Would like to add similar support here.
> >
> >Please let me know your opinion on the same.
> >
> >[1] https://blueprints.launchpad.net/glance/+spec/block-subtractive-operations
> >
> >
> >Thank you,
> >
> >Abhishek Kekane

You'll probably need some way to actually perform such migrations when
needed. In Cinder we've introduced guidelines [1], which allow us to
ALTER or DROP a column with a process stretching through 2-3 releases.

Nova does a little better by not allowing nova-compute to access the DB
(nova-conductor is acting as a proxy).

Also note that unit test won't prevent you from all of the cases. It
won't for example detect DB-specific migrations written in plain SQL as
in [2].

[1] http://specs.openstack.org/openstack/cinder-specs/specs/mitaka/online-schema-upgrades.html
[2] https://review.openstack.org/#/c/190300

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