[ckan-dev] sqlalchemy migrate, dependency issues.

[David Raznick]

Hello

The correct way to do this will involve, based on my understanding and your
comments.

 * changing the setup.py dependencies for sqlalchemy-migrate and sqlalchemy
to their latest versions.
 * running the migrate script on the repository (or changing the repository
scripts manually).
 * checking in both these changes at once.

Along side this we should make one of these is in place.  In order of my
preference.

1. We have a script on app launch that automatically updates the database to
the latest version of the migrate-repository it has got.
2. We should make sure the app will not run (i.e raise an exception) until
the db update is done and it is in sync with the latest migrate-repository
version it has checked out.
3. We add something to the fabfile to run update db every ckan update, and
we always update using the fabfile.
4. We make it an absolute process that after any upgrade we do an update db.

At the moment I imagine we have got a slightly less strict version of 4
going on?  am I right?

The issue I see with 1 is that if the application is started as an apache
wsgi script with multiple processes there could be a lot of pain (we do not
want to upgrade a database from 2 processes) and this would be hard to
debug.  We would need some kind of update db lock.

Basically every instances database HAS to be in sync with the latest version
of the repository it has got.  If this is not assured we are not in a good
place.

I am happy to do the first 3 points (as they are easy) but only if we are
confident that one of the above 4 points are in place.

Thanks

David



On Wed, Jan 26, 2011 at 8:30 PM, David Read <david.read at okfn.org> wrote:

> Well it's only an issue when we upgrade CKAN, so let's focus on those
> that we do need to migrate. I'm needing on gvt servers later this week
> so I'll have a play if David doesn't get there first. I suggest we
> check-in a change that changes the requirement in setup.py to
> sqlalchemy>=0.6 and a migration script that prints a warning showing
> the need to run this migrate tool (assuming the migrate script can't
> run it itself?).
>
>
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