Open Stack

> On Wed, 2013-02-27 at 08:09 -0500, Eoghan Glynn wrote:
> > Folks,
> > 
> > When looking into an error encountered on a keystone db sync,
> > I noticed some apparent strangeness in the way keystone schema
> > migrations have been managed.
> > 
> > Specifically the *rewriting* of schema migration history, see:
> > 
> >   https://github.com/openstack/keystone/commit/5bc46d86
> > 
> > In my (albeit imperfect) understanding of sqlalchemy-migrate, this
> > reordering seems to defeat the whole purpose of step-wise
> > reversible
> > migration.
> > 
> > Would it even be possible to migrate a grizzly-2 deployment to
> > grizzly-3 with that re-ordering in place?
> > 
> > Maybe I've missed something here, but I'd appreciate some clarity
> > on what is considered community best practice in terms of changes
> > to the migration sequence.
> > 
> > Previously I would have assumed something like ...
> > 
> > Invariants we maintain:
> > 
> >  - DB schemas must always be migrate-able across milestone releases
> 
> (snip good stuff)
> 
> It's more than just across milestone releases, we should support
> upgrading from commit to commit. 

Yeah I debated that point internally while drafting the email and 
came down on the side of the more loose invariant, as milestones
are "stood over" by the community in a more explicit way than
individual commits.

But in fairness to the trunk chasers out there, and given how
central schema migration is to any upgrade, I see your point
that maintaining commit-to-commit migration is really where
we'd want to be.

Cheers,
Eoghan

> In Nova, at least, we're trying hard to
> avoid messing up those who are deploying continuously. I'd expect any
> nova-core member to reject this patch immediately.
> 
> What I really don't understand is how this concern wasn't raised in
> the
> review at all:
> 
>   https://review.openstack.org/19780
> 
> Cheers,
> Mark.
> 
> 
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