[openstack-dev] savann-ci, Re: [savanna] Alembic migrations and absence of DROP column in sqlite
Trevor McKay
tmckay at redhat.com
Wed Feb 5 16:56:02 UTC 2014
Hi Sergey,
Is there a bug or a blueprint for this? I did a quick search but
didn't see one.
Thanks,
Trevor
On Wed, 2014-02-05 at 16:06 +0400, Sergey Kolekonov wrote:
> I'm currently working on moving on the MySQL for savanna-ci
>
>
> On Wed, Feb 5, 2014 at 3:53 PM, Sergey Lukjanov
> <slukjanov at mirantis.com> wrote:
> Agreed, let's move on to the MySQL for savanna-ci to run
> integration tests against production-like DB.
>
>
> On Wed, Feb 5, 2014 at 1:54 AM, Andrew Lazarev
> <alazarev at mirantis.com> wrote:
> Since sqlite is not in the list of "databases that
> would be used in production", CI should use other DB
> for testing.
>
>
> Andrew.
>
>
> On Tue, Feb 4, 2014 at 1:13 PM, Alexander Ignatov
> <aignatov at mirantis.com> wrote:
> Indeed. We should create a bug around that and
> move our savanna-ci to mysql.
>
> Regards,
> Alexander Ignatov
>
>
>
> On 05 Feb 2014, at 01:01, Trevor McKay
> <tmckay at redhat.com> wrote:
>
> > This brings up an interesting problem:
> >
> > In https://review.openstack.org/#/c/70420/
> I've added a migration that
> > uses a drop column for an upgrade.
> >
> > But savann-ci is apparently using a sqlite
> database to run. So it can't
> > possibly pass.
> >
> > What do we do here? Shift savanna-ci tests
> to non sqlite?
> >
> > Trevor
> >
> > On Sat, 2014-02-01 at 18:17 +0200, Roman
> Podoliaka wrote:
> >> Hi all,
> >>
> >> My two cents.
> >>
> >>> 2) Extend alembic so that op.drop_column()
> does the right thing
> >> We could, but should we?
> >>
> >> The only reason alembic doesn't support
> these operations for SQLite
> >> yet is that SQLite lacks proper support of
> ALTER statement. For
> >> sqlalchemy-migrate we've been providing a
> work-around in the form of
> >> recreating of a table and copying of all
> existing rows (which is a
> >> hack, really).
> >>
> >> But to be able to recreate a table, we
> first must have its definition.
> >> And we've been relying on SQLAlchemy schema
> reflection facilities for
> >> that. Unfortunately, this approach has a
> few drawbacks:
> >>
> >> 1) SQLAlchemy versions prior to 0.8.4 don't
> support reflection of
> >> unique constraints, which means the
> recreated table won't have them;
> >>
> >> 2) special care must be taken in 'edge'
> cases (e.g. when you want to
> >> drop a BOOLEAN column, you must also drop
> the corresponding CHECK (col
> >> in (0, 1)) constraint manually, or SQLite
> will raise an error when the
> >> table is recreated without the column being
> dropped)
> >>
> >> 3) special care must be taken for 'custom'
> type columns (it's got
> >> better with SQLAlchemy 0.8.x, but e.g. in
> 0.7.x we had to override
> >> definitions of reflected BIGINT columns
> manually for each
> >> column.drop() call)
> >>
> >> 4) schema reflection can't be performed
> when alembic migrations are
> >> run in 'offline' mode (without connecting
> to a DB)
> >> ...
> >> (probably something else I've forgotten)
> >>
> >> So it's totally doable, but, IMO, there is
> no real benefit in
> >> supporting running of schema migrations for
> SQLite.
> >>
> >>> ...attempts to drop schema generation
> based on models in favor of migrations
> >>
> >> As long as we have a test that checks that
> the DB schema obtained by
> >> running of migration scripts is equal to
> the one obtained by calling
> >> metadata.create_all(), it's perfectly OK to
> use model definitions to
> >> generate the initial DB schema for running
> of unit-tests as well as
> >> for new installations of OpenStack (and
> this is actually faster than
> >> running of migration scripts). ... and if
> we have strong objections
> >> against doing metadata.create_all(), we can
> always use migration
> >> scripts for both new installations and
> upgrades for all DB backends,
> >> except SQLite.
> >>
> >> Thanks,
> >> Roman
> >>
> >> On Sat, Feb 1, 2014 at 12:09 PM, Eugene
> Nikanorov
> >> <enikanorov at mirantis.com> wrote:
> >>> Boris,
> >>>
> >>> Sorry for the offtopic.
> >>> Is switching to model-based schema
> generation is something decided? I see
> >>> the opposite: attempts to drop schema
> generation based on models in favor of
> >>> migrations.
> >>> Can you point to some discussion threads?
> >>>
> >>> Thanks,
> >>> Eugene.
> >>>
> >>>
> >>>
> >>> On Sat, Feb 1, 2014 at 2:19 AM, Boris
> Pavlovic <bpavlovic at mirantis.com>
> >>> wrote:
> >>>>
> >>>> Jay,
> >>>>
> >>>> Yep we shouldn't use migrations for
> sqlite at all.
> >>>>
> >>>> The major issue that we have now is that
> we are not able to ensure that DB
> >>>> schema created by migration & models are
> same (actually they are not same).
> >>>>
> >>>> So before dropping support of migrations
> for sqlite & switching to model
> >>>> based created schema we should add tests
> that will check that model &
> >>>> migrations are synced.
> >>>> (we are working on this)
> >>>>
> >>>>
> >>>>
> >>>> Best regards,
> >>>> Boris Pavlovic
> >>>>
> >>>>
> >>>> On Fri, Jan 31, 2014 at 7:31 PM, Andrew
> Lazarev <alazarev at mirantis.com>
> >>>> wrote:
> >>>>>
> >>>>> Trevor,
> >>>>>
> >>>>> Such check could be useful on alembic
> side too. Good opportunity for
> >>>>> contribution.
> >>>>>
> >>>>> Andrew.
> >>>>>
> >>>>>
> >>>>> On Fri, Jan 31, 2014 at 6:12 AM, Trevor
> McKay <tmckay at redhat.com> wrote:
> >>>>>>
> >>>>>> Okay, I can accept that migrations
> shouldn't be supported on sqlite.
> >>>>>>
> >>>>>> However, if that's the case then we
> need to fix up savanna-db-manage so
> >>>>>> that it checks the db connection info
> and throws a polite error to the
> >>>>>> user for attempted migrations on
> unsupported platforms. For example:
> >>>>>>
> >>>>>> "Database migrations are not supported
> for sqlite"
> >>>>>>
> >>>>>> Because, as a developer, when I see a
> sql error trace as the result of
> >>>>>> an operation I assume it's broken :)
> >>>>>>
> >>>>>> Best,
> >>>>>>
> >>>>>> Trevor
> >>>>>>
> >>>>>> On Thu, 2014-01-30 at 15:04 -0500, Jay
> Pipes wrote:
> >>>>>>> On Thu, 2014-01-30 at 14:51 -0500,
> Trevor McKay wrote:
> >>>>>>>> I was playing with alembic migration
> and discovered that
> >>>>>>>> op.drop_column() doesn't work with
> sqlite. This is because sqlite
> >>>>>>>> doesn't support dropping a column
> (broken imho, but that's another
> >>>>>>>> discussion). Sqlite throws a syntax
> error.
> >>>>>>>>
> >>>>>>>> To make this work with sqlite, you
> have to copy the table to a
> >>>>>>>> temporary
> >>>>>>>> excluding the column(s) you don't
> want and delete the old one,
> >>>>>>>> followed
> >>>>>>>> by a rename of the new table.
> >>>>>>>>
> >>>>>>>> The existing 002 migration uses
> op.drop_column(), so I'm assuming
> >>>>>>>> it's
> >>>>>>>> broken, too (I need to check what the
> migration test is doing). I
> >>>>>>>> was
> >>>>>>>> working on an 003.
> >>>>>>>>
> >>>>>>>> How do we want to handle this? Three
> good options I can think of:
> >>>>>>>>
> >>>>>>>> 1) don't support migrations for
> sqlite (I think "no", but maybe)
> >>>>>>>>
> >>>>>>>> 2) Extend alembic so that
> op.drop_column() does the right thing
> >>>>>>>> (more
> >>>>>>>> open-source contributions for us,
> yay :) )
> >>>>>>>>
> >>>>>>>> 3) Add our own wrapper in savanna so
> that we have a drop_column()
> >>>>>>>> method
> >>>>>>>> that wraps copy/rename.
> >>>>>>>>
> >>>>>>>> Ideas, comments?
> >>>>>>>
> >>>>>>> Migrations should really not be run
> against SQLite at all -- only on
> >>>>>>> the
> >>>>>>> databases that would be used in
> production. I believe the general
> >>>>>>> direction of the contributor community
> is to be consistent around
> >>>>>>> testing of migrations and to not run
> migrations at all in unit tests
> >>>>>>> (which use SQLite).
> >>>>>>>
> >>>>>>> Boris (cc'd) may have some more to say
> on this topic.
> >>>>>>>
> >>>>>>> Best,
> >>>>>>> -jay
> >>>>>>>
> >>>>>>>
> >>>>>>>
> _______________________________________________
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> >>>>>>
> >>>>>>
> >>>>>>
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> >>>>>
> >>>>
> >>>>
> >>>>
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> --
> Sincerely yours,
> Sergey Lukjanov
> Savanna Technical Lead
> Mirantis Inc.
>
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