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/ 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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