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Do you reckon that the process that led to creating a migration like [1]
should also be documented in devref?
That might be helplful for developers, unless that process is already
documented elsewhere.

Salvatore


[1] https://review.openstack.org/#/c/202013/1

On 15 July 2015 at 15:54, Mike Bayer <mbayer at redhat.com> wrote:

>
>
> On 7/15/15 9:26 AM, Ihar Hrachyshka wrote:
>
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA256
>>
>> 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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>>
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