On Apr 26, 2012, at 12:03 PM, Monty Taylor wrote:
> > > On 04/26/2012 10:14 AM, Sean Dague wrote: >> On 04/25/2012 05:17 PM, Vishvananda Ishaya wrote: >>> The main issue is when the relevant tables are moved into a separate >>> service a la quantum or cinder. We can't keep referential integrity >>> across multiple databases, so the foreign keys in this case need to be >>> removed. It leads to an odd situation when there is still an internal >>> implementation in addition to the external implementation because the >>> internal implementation no longer has foreign keys. >>> >>> As an example, we used to have foreign key relationships between >>> instances and networks. We can no longer have these because we support >>> networks declared externally. The internal network management now has no >>> referential integrity, but this is the price we pay for separation of >>> concerns. We are going through a similar set of relationship-breaking >>> with the volume code. >> >> There are definitely the practical aspects of where this "can't" be done >> because the services have split out, and I think that's fine. >> >> But enforcing the ref constraints where possible just provides another >> level of safety in the data. A policy where we break FK relationships if >> the preferred core model is 2 services (i.e. Nova / Quantum), but we add >> FK constraints within a service might be a good idea. > > I think the real key is to have a config option to tell sqlalchemy to > not, even if we're running innodb, add the foreign keys to the DDL sent > to the database. If sqlalchemy doesn't have that ability, we should > write it and contribute it, because anyone using MySQL at scale via > sqlalchemy actually wants the feature, whether they recognize it yet or not. > I registered a blueprint for this: https://blueprints.launchpad.net/nova/+spec/disable-fkeys-by-config Take care, Lorin -- Lorin Hochstein Lead Architect - Cloud Services Nimbis Services, Inc. www.nimbisservices.com
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