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On Aug 29, 2014, at 7:23 AM, Alan Pevec <apevec at gmail.com> wrote:

>> It seems that currently it's hard to backport any database schema fix to
>> Neutron [1] which uses alembic to manage db schema version. Nova has the
>> same issue before
>> and a workaround is to put some placeholder files before each release.
>> So first do we allow db schema fixes to be backport to stable for Neutron ?
> 
> DB schema backports was a topic at StableBranch session last design
> summit [*] and policy did not change: not allowed in general but
> exceptions could always be discussed on stable-maint list.
> 
>> If we do, then how about put some placeholder files similar to Nova at the
>> end of each release cycle? or we have some better solution for alembic.
> 
> AFAIK you can't have placeholders in alembic, there was an action item
> from design session for Mark to summarize his best practices for db
> backports.


Alembic doesn’t need “placeholder” files, if we’re referring to the practice with migrate to have empty migration files present so that new migrations can be spliced in.   Alembic migrations can be spliced anywhere in the series.  The only current limitation, which is on deck to be opened up, is that the migrations ultimately have to be arranged linearly in some way (e.g. if two different environments are the product of two branches, and need to run the same series of migrations, but one needs to skip certain files and the other needs to skip others, only those migrations that are needed on each are applied.  But SQLalchemy-migrate certainly has no capability for that either).   If this issue needs to be fast-tracked I can move my efforts there.