[openstack-dev] [neutron][db] online schema upgrades

Mike Bayer mbayer at redhat.com
Tue Jun 16 15:58:28 UTC 2015

On 6/16/15 11:41 AM, Ihar Hrachyshka wrote:
> Hash: SHA256
> - - instead of migrating data with alembic rules, migrate it in runtime.
> There should be a abstraction layer that will make sure that data is
> migrated into new schema fields and objects, while preserving data
> originally stored in 'old' schema elements.
> That would allow old neutron-server code to run against new schema (it
> will just ignore new additions); and new neutron-server code to
> gradually migrate data into new columns/fields/tables while serving user
> s.
Hi Ihar -

I was in the middle of writing a spec for neutron online schema 
migrations, which maintains "expand / contract" workflow but also 
maintains Alembic migration scripts.   As I've stated many times in the 
past, there is no reason to abandon migration scripts, while there are 
many issues related to abandoning the notion of the database in a 
specific versioned state as well as the ability to script any migrations 
whatsoever.   The spec amends Nova's approach and includes upstream 
changes to Alembic such that both approaches can be supported using the 
same codebase.

- mike

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