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On 1/26/2015 11:35 AM, Matt Riedemann wrote:
> The change to add DB2 support to nova has hit a snag in the 247
> migration [1] where it's altering the pci_devices.deleted column to be
> nullable=True to match the model (it was defined nullable=False in the
> 216 migration which didn't match the model).
>
> The problem is DB2 won't allow unique constraints over nullable columns
> and the unique constraint is required for the foreign key constraint
> between pci_devices and compute_nodes via the compute_node_id column in
> pci_devices (DB2 requires that a FKey be on a column that's in a unique
> or primary key constraint, and those must be non-nullable with DB2).
>
> So I'm kind of stuck with what to do here. As discussed in the change
> with Johannes (and Jay Pipes in IRC a week ago), it's kind of silly that
> the deleted column is nullable (am I missing something), but that's
> defined in the SoftDeleteMixin in oslo.db [2] so it's pervasive.
>
> I see our options as (1) diverge the pci_devices.deleted model for DB2
> and/or (2) add a HardDeleteMixin to oslo.db where deleted is
> nullable=False, then work that into nova but it's going to require a big
> migration (I'm thinking FKey drops, UC drops, table alterations, then
> re-add the UCs and FKeys over the deleted columns that were altered,
> plus possibly a CLI to scan the database looking for rows where deleted
> is NULL, like we did for instances.uuid when making that non-nullable).
>
> Option (1) is obviously a short-term fix and in my opinion relatively
> painless since we aren't generating the DB schema from the modeles (yet,
> until Johannes has his vision realized :) ).  Option (2) is going to
> take some work, but I think it makes sense as something to do regardless
> of DB2's restrictions here.
>
> Thoughts?
>
> [1]
> https://review.openstack.org/#/c/69047/38/nova/db/sqlalchemy/migrate_repo/versions/247_nullable_mismatch.py
>
> [2]
> http://git.openstack.org/cgit/openstack/oslo.db/tree/oslo_db/sqlalchemy/models.py#n122
>
>

This is coming up again here now:

https://review.openstack.org/#/c/153123/6/nova/db/sqlalchemy/migrate_repo/versions/277_fix_unique_constraint_for_compute_node.py

-- 

Thanks,

Matt Riedemann