[openstack-dev] [all][tc] SQL Schema Downgrades and Related Issues

Boris Bobrov bbobrov at mirantis.com
Fri Jan 30 08:44:00 UTC 2015

On Friday 30 January 2015 01:01:00 Boris Bobrov wrote:
> On Thursday 29 January 2015 22:06:25 Morgan Fainberg wrote:
> > I’d like to propose we stop setting the expectation that a downwards
> > migration is a “good idea” or even something we should really support.
> > Offering upwards-only migrations would also simplify the migrations in
> > general. This downward migration path is also somewhat broken by the
> > migration collapses performed in a number of projects (to limit the
> > number of migrations that need to be updated when we change a key
> > component such as oslo.db or SQL-Alchemy Migrate to Alembic).
> > 
> > Are downward migrations really a good idea for us to support? Is this
> > downward migration path a sane expectation? In the real world, would any
> > one really trust the data after migrating downwards?
> Frankly, I don't see a case when a downgrade from n to (n - 1) in
> development cannot be replaced with a set of fixtures and upgrade from 0
> to (n - 1).
> If we assume that upgrade can possible break something in production, we
> should not rely on fixing by downgrading the schema, because a) the code
> depends on the latest schema and b) "break" can be different and
> unrecoverable.
> IMO downward migrations should be disabled. We could make a survey though,
> maybe someone has a story of using them in the fields.

I've made a little survey and there are people who used downgrades for 
debugging of different OpenStack releases.

So, I think I'm +1 on Mike Bayer's opinion.

Best regards,
Boris Bobrov

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