[katello-devel] Katello schema - documentation and questions

[Lukas Zapletal]

Ok so it's doable. What is your approach in Cloud Engine by the way?

LZ

On Wed, Aug 01, 2012 at 08:33:22AM -0400, Hugh Brock wrote:
> On Mon, Jul 30, 2012 at 12:02:57PM +0200, Lukas Zapletal wrote:
> > By the way, what are the biggest concerns in regard to using foreign
> > keys and rails? What is the issue?
> > 
> Heh... the issue is that Active Record is quite happy to define
> relationships that would traditionally have required proper
> referential constraints in a database, without defining any
> constraints. So there is absolutely nothing stopping me (or a bug in
> Active Record) from deleting rows in the DB that are referenced by
> other rows, which can break your whole app horribly.
> 
> The solution is simply to add proper constraints in your
> migrations. However most folks in the modern web-scale world seem
> happy to live with this level of risk and don't bother with the
> constraints, despite the fact that it makes us dinosaurs
> uncomfortable...
> 
> --Hugh
> 
> 
> > 
> > On Fri, Jul 27, 2012 at 10:14:21AM +0200, Miroslav Suchy wrote:
> > > While working on APIDocumentationEfforts [1] I wanted some nice
> > > documentation of our schema. I find we have none, so I created one:
> > >   http://miroslav.suchy.cz/katello/katelloschema.html
> > > It is created by PostgreSQL Autodoc [2].
> > > 
> > > To my surprise it does not contain foreign keys and very few indexes.
> > > First I thought it is bug in Autodoc. But then - to my horor - I
> > > find it is not bug. We do not have foreign keys and indexes on most
> > > tables!
> > > 
> > > So we have two issues.
> > > 
> > > 1) Indexes:
> > > E.g. table user_notices, which purpose is IMHO always to live
> > > between two JOINS and is school example where indexes should be
> > > used, do not have indexes.
> > > I can go through schema and suggest where we should create indexes.
> > > I do not expect that it would cause any problem.
> > > Objections here?
> > > 
> > > 2) Foreign keys:
> > > I read about foreign keys and ruby and I learned that community
> > > around Rails think that application level is best/enough to keep
> > > data consistency. So I expect a lot of discussion here.
> > > Let me share my point of view here:
> > > IMO data consistency should be work of database engine.
> > > There are two examples:
> > > a) when our code is fatally interrupted. E.g.
> > > 
> > > src/app/models/glue/pulp/repo.rb:
> > >   def destroy_repo_orchestration
> > >     pre_queue.create(:name => "remove product content :
> > > #{self.name}", :priority => 1, :action => [self, :del_content])
> > > [.. FATAL CRASH HERE ...]
> > >     pre_queue.create(:name => "delete pulp repo : #{self.name}",
> > > :priority => 2, :action => [self, :destroy_repo])
> > >   end
> > > 
> > > You will end up with repository with product id, which does not exist.
> > > Foreign keys with ON DELETE CASCADE solve this.
> > > 
> > > b) But even if we solve all issues in our code (e.g start using
> > > transactions), there is problems with humans.
> > > During my 5 years in RHN Satellite team I seen non trivial numbers
> > > of Customers issues, where either customer or even TAM(!) run
> > > directly SQL commands, which without foreign keys would result in
> > > inconsistent database.
> > > Using foreign keys seems doable:
> > >  https://github.com/matthuhiggins/foreigner
> > >  https://github.com/jenseng/immigrant
> > > So it should be basically two gems, few lines of code and some testing.
> > > 
> > > Your opinions?
> > > 
> > > 
> > > [1] https://fedorahosted.org/katello/wiki/APIDocumentationEfforts
> > > [2] http://www.rbt.ca/autodoc/ (available in Fedora as package)
> > > 
> > > Mirek
> > > 
> > > _______________________________________________
> > > katello-devel mailing list
> > > katello-devel at redhat.com
> > > https://www.redhat.com/mailman/listinfo/katello-devel
> > 
> > -- 
> > Later,
> > 
> >  Lukas "lzap" Zapletal
> >  #katello #systemengine
> > 
> > _______________________________________________
> > katello-devel mailing list
> > katello-devel at redhat.com
> > https://www.redhat.com/mailman/listinfo/katello-devel
> 
> -- 
> == Hugh Brock, hbrock at redhat.com                                   ==
> == Engineering Manager, Cloud BU                                   ==
> == Aeolus Project: Manage virtual infrastructure across clouds.    ==
> == http://aeolusproject.org                                        ==
> 
> "I know that you believe you understand what you think I said, but I’m
> not sure you realize that what you heard is not what I meant."
> --Robert McCloskey
> 
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-- 
Later,

 Lukas "lzap" Zapletal
 #katello #systemengine