[ZODB-Dev] Re: so your coming from the rdbms world tutorial?

[Roché Compaan]

On Sat, 2008-03-22 at 04:55 -0400, Sean Allen wrote:
> On Mar 22, 2008, at 3:50 AM, Roché Compaan wrote:
> 
> > On Fri, 2008-03-21 at 22:49 -0400, Sean Allen wrote:
> >> And we want to change the the description of Widget B and have that
> >> change appear for everything, how do I do that?
> >> basically, I want all LineItems for Widget A to all refer to a single
> >> instance of Product.
> >
> > If you simply assign the product to an attribute on the line item, it
> > will create a reference in the ZODB. And you can use zc.relation to
> > index and query the relation.
> >
> > # get the product from your products container:
> > product = productfolder['ProductXYZ']
> > # assign it to the line item instance
> > lineitem.product = product
> >
> > It's really that simple! If you change the description attribute of  
> > the
> > referenced product, all line items referencing it will show the new
> > description.
> 
> 
> Ha! Ok.
> 
> Questions then from there.
> 
> Why not store each object type,
> 
> customer, order etc in their own folders?

You could, and I understand that you want to do so coming from a RDBMS
world, but if you are working with objects then you have the luxury of
organising content in a way that is closer to reality. I think it is
rather convenient to store a customer's orders inside it.

There is another good reason - it makes a lot more sense to distribute
object creation to different containers in the ZODB to avoid write
conflict errors.

> 
> is there a reason to have a folder that contains a more complete graph?
> what advantages would that have? speed of access?

What do you mean with "more complete graph"?

> 
> --
> 
> the database i am looking at moving over has
> 
> 1.2 million entries in a transactions table
> 980,000 orders
> 775,000 customers
> 1.5 million order items

I think these numbers are quite manageable. But think carefully what
kind of queries you want to do on the data. You have a very rich query
language in SQL that allows the construction of complex queries and it
will come naturally to you. To do the same in the ZODB will take careful
planning.

> and probably another 600,000 other assorted entires that would
> be needed in an oo scenario ( tons of join table entries get ditched  
> tho, nice! )
> 
> what type of server setup etc would be needed to handle that load
> considering that currently, 40,000 new orders go in a month
> along with the corresponding numbers of customers etc.

It depends a lot on the concurrency. It is usually advisable to not
compromise on server architecture, but be sure to get a server with
enough RAM (nothing less than 4GB) and very fast disks.

-- 
Roché Compaan
Upfront Systems                   http://www.upfrontsystems.co.za