[openstack-dev] [oslo.db] [ndb] ndb namespace throughout openstack projects

Dan Smith dms at danplanet.com
Mon Jul 24 14:11:38 UTC 2017

> So, I see your point here, but my concern here is that if we *modify* an
> existing schema migration that has already been tested to properly apply
> a schema change for MySQL/InnoDB and PostgreSQL with code that is
> specific to NDB, we introduce the potential for bugs where users report
> that the same migration works sometimes but fails other times.

This ^.

The same goes for really any sort of conditional in a migration where
you could end up with different schema. I know that is Mike's point (to
not have that happen) but I think the difficulty is proving and
guaranteeing (now and going forward) that they're identical. Modifying a
migration in the past is like a late-breaking conditional.

> I would much prefer to *add* a brand new schema migration that handles
> conversion of the entire InnoDB schema at a certain point to an
> NDB-compatible one *after* that point. That way, we isolate the NDB
> changes to one specific schema migration -- and can point users to that
> one specific migration in case bugs arise. This is the reason that every
> release we add a number of "placeholder" schema migration numbered files
> to handle situations such as these.



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