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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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