openstack team mailing list archive

[Christoph Thiel <cthiel@xxxxxxxx>]

On Thu, Apr 19, 2012 at 07:32:15PM +0200, Bernhard M. Wiedemann wrote:
> On 04/12/2012 02:35 PM, J. Daniel Schmidt wrote:
> > Dear Developers,
> > 
> > While testing our SUSE OpenStack packages we hit a nasty bug and
> > reported it as:  https://bugs.launchpad.net/keystone/+bug/972502
> > 
> > We found out that the underlying cause was a lack of referential
> > integrity[1] using sqlite or mysql. When we tried to reproduce this
> > issue on postgresql the usage of foreign keys greatly helped to
> > find the cause.
> > 
> > In order to prevent further inconsistencies we created a patch that
> > added more foreign keys: https://review.openstack.org/6216
> > 
> > One reviewer commented:
> >> i don't approve of adding foreign keys, and we should probably
> >> remove the existing ones (in UserTenantMembership and in
> >> Endpoint)
> > 
> > and on 
> > https://review.openstack.org/#patch,sidebyside,6216,3,keystone/identity/backends/sql.py
> >>
> > 
> we shouldn't be using foreign keys at all, they are a crutch that are not
> >> available everywhere
> > 
> > This was a surprising answer to us as the usage of the foreign keys
> > revealed the inconsistency in the first place. So removing them
> > elsewhere does in no way improve the situation, it even does not
> > help for mysql and sqlite, as SQLAlchemy abstracts them away. We
> > also found similar bugs elsewhere:
> > 
> > * https://bugs.launchpad.net/keystone/+bug/959294 *
> > https://bugs.launchpad.net/keystone/+bug/973243 *
> > https://bugs.launchpad.net/keystone/+bug/974199
> > 
> > In our point of view foreign keys should be used in all possible
> > places. This would not harm any database that does not support them
> > but helps all of us to find data inconsistencies and related bugs,
> > which leads to faster development with fewer bugs.
> > 
> > 
> > What is your take on these things? How would you take care of data
> > consistency otherwise?
> > 
> > 
> > Thank you for your feedback, Berhard M. Wiedemann J. Daniel
> > Schmidt
> > 
> > [1]: http://en.wikipedia.org/wiki/Referential_integrity
> 
> 
> Just saw another bug, that would have been caught earlier with foreign
> keys:
> https://bugs.launchpad.net/nova/+bug/754900
> 
> So was this issue discussed on the OpenStack Summit?

Yes, I raised this in the "Standardizing database management across
projects"[1] session and everybody attending that sessions agreed that
it's a good idea.

However, https://review.openstack.org/#/c/6216/ is still open ;(


Best
Christoph

[1] http://folsomdesignsummit2012.sched.org/event/40adf6c240f7ed1fab82e19e8e55dc24
-- 
Christoph Thiel, Project Manager, SUSE Cloud Infrastructure

SUSE LINUX Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer, HRB 16746 (AG Nürnberg)