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From: Jan Lehnardt <jan@apache.org>
To: dev@couchdb.apache.org
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Subject: Re: Multi-database application: is that possible?
Date: Sat, 20 Dec 2008 15:39:20 +0100
References: <7d8fb2e90812200601v5652f1d2hd52997786639514f@mail.gmail.com>

Hi,

On 20 Dec 2008, at 15:01, Andrea Schiavini wrote:

> Hallo!
> I've been recently thinking about the possible different design  
> choices
> offered by CouchDB, and - more generally - by Document Oriented  
> Databases.
> Specifically, I considered the case of web applications like  
> Amazon.com,
> where they need to have full consistency in some specific "fields",  
> like
> item availability;

They actually don't. Enforcing consistency at their size is a lot more  
expensive
than saying: "Sorry, we know we told you you can buy this, but we were  
wrong,
here's a $20 cupon for your next purchase."


> still, in the biggest part of their database (the one
> about item descriptions, user details etc.), they can get huge  
> benefits from
> a document oriented database.
> How do they solve the problem of consistency? I think a good  
> solution could
> be to use a two-database design, with a standard SQL database to  
> store only
> item availability and critical data, and another document oriented  
> database
> for everything else. Of course, a cross database relation has to be  
> built.
> I've read that SimpleDB by amazon also offers eventual consistency,  
> like
> CouchDB; and they also state that they're using SimpleDB for the
> amazon.comwebsite. So, how do they solve this problem?

Amazon's CEO Werner Vogels describes their system in detail:
http://www.allthingsdistributed.com/2007/10/amazons_dynamo.html


Cheers
Jan
--