Open Stack

Actually no confusion. :-) Joe Gordon just made me realize that I didn't
really explain why we had that policy.

That really should have been a follow up to my own post, not yours. Sorry
if I made it look like I was arguing with you, which I wasn't.. :-)

We're all good.

Sean Dague
http://dague.net
On Oct 31, 2013 12:12 PM, "Jay Pipes" <jaypipes at gmail.com> wrote:

> On 10/31/2013 11:56 AM, Sean Dague wrote:
>
>> On 10/31/2013 11:23 AM, Jay Pipes wrote:
>>
>>> On 10/31/2013 08:01 AM, Sean Dague wrote:
>>>
>>>> So there is a series of patches starting with -
>>>> https://review.openstack.org/#**/c/53417/<https://review.openstack.org/#/c/53417/>that go back and radically
>>>> change existing migration files.
>>>>
>>>> This is really a no-no, unless there is a critical bug fix that
>>>> absolutely requires it. Changing past migrations should be considered
>>>> with the same level of weight as an N-2 backport, only done when there
>>>> is huge upside to the change.
>>>>
>>>> I've -2ed the first 2 patches in the series, though that review applies
>>>> to all of them (I figured a mailing list thread was probably more useful
>>>> than -2ing everything in the series).
>>>>
>>>> There needs to be really solid discussion about the trade offs here
>>>> before contemplating something as dangerous as this.
>>>>
>>>
>>> +1
>>>
>>
>> There is a very real reason why we have a firm stance on this. There are
>> a huge number of OpenStack instances out in the field, at all sorts of
>> different past versions. We really try to promise that you can always
>> forward upgrade your database.
>>
>> If you go back and change an old migration, you have not forked the
>> past. Some people will have already taken that migration, and they have
>> one view of the world, others haven't yet, they hit your updated
>> version, and they now have different database. So 2 people with Havana
>> would no longer be guaranteed to have the same data model set up by us.
>>
>> It's easy to believe that "this change is really straight forward, it
>> will be exactly the same model", but if it isn't, in any way, exactly
>> the same (even in a way that we didn't realize yet that it mattered),
>> you've forked the past. And that makes supporting users in these various
>> forked versions of the world impossible.
>>
>> Migrations are basically idempotent. If you want to clean things up, do
>> them in a new migration. Don't touch an old one unless it is causing
>> corruption to someone's data so that fixing it with a future migration
>> is not an option.
>>
>
> LOL, I was +1'ing your thoughts, not +1'ing the proposal to have a solid
> discussion about the trade-offs :)
>
> Sorry for the confusion!
> -jay
>
>
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