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On 7/15/15 9:26 AM, Ihar Hrachyshka wrote:
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> Hi all,
>
> since it's a high impact change in the migration tree, I wanted to
> drop an email to everyone affected (basically, anyone who wants to
> introduce a new migration from now on).
>
> So there was a proposal to split migration rules into independent
> branches, with one 'expand' branch containing only those rules that
> are safe to apply while neutron-server is running. Proposal is at:
>
> http://specs.openstack.org/openstack/neutron-specs/specs/liberty/online-
> schema-migrations.html
>
> And the first patch to implement it just landed in neutron:
>
> http://git.openstack.org/cgit/openstack/neutron/commit/?id=c7acfbabdc13e
> d2a73bdbc6275af8063b8c1eb2f
>
> - From now on,
>
> - - there are multiple alembic heads for any database state;
> - - there is a new file structure under
> neutron/db/migration/versions/alembic_versions/{cycle}_{branch};
> - - you may need to split your migrations into pieces (for expand and
> contract branches, respectively, depending on the character of schema
> changes; more details in the spec);
> - - 'neutron-db-manage upgrade head' still applies all heads;
> - - I'd like to rearrange migration trees for *aas repos in the same
> way, though neutron-db-manage still supports the old file layout.
>
> To get an example of how the split would look like for existing
> migration rules in review, I took Kevin's patch for RBAC:
>
> https://review.openstack.org/191707
>
> And transformed it into something that adopts the new file layout:
>
> https://review.openstack.org/202013
>
> Changes I made:
> - - split migration script into two pieces;
> - - updated HEADS file;
> - - made the contract phase script depends_on the expand one;
>
> Note that 'neutron-db-manage revision --autogenerate' command does not
> yet filter operations into corresponding branches, though we would
> like to have it in L once new alembic is released.

This API is in master and will be the focus of the 0.8 release. This is 
a major refactor so I'm still working out backwards-compatibility stuff 
as well as getting some more pluggability into autogenerate while we're 
at it.   The documentation for the specific aspect of "filtering 
operations during autogenerate" is up at 
http://alembic.readthedocs.org/en/latest/api/autogenerate.html#customizing-revision-generation.


>
> Ihar
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