I saw this visualization of where the various nosql databases fit on
the CAP Theorem triangle. CAP says there are three primary concerns
you must balance when choosing a data management system: Consistency,
Availability, and Partition tolerance. Furthermore, you can only pick
2.

http://blog.nahurst.com/visual-guide-to-nosql-systems

According to this, Riak, SimpleDB, Cassandra and CouchDB all sit on
the AP side, whereas MongoDB and BigTable sit on the CP side. Most
relational databases sit on the CA side.

Tom

On Tue, Dec 14, 2010 at 12:11 PM, Luciano Ramalho <[log in to unmask]> wrote:
> On Tue, Dec 14, 2010 at 11:58 AM, Bill Dueber <[log in to unmask]> wrote:
>> Oops. I just found a better overview than I can provide, at
>> http://www.mongodb.org/display/DOCS/Comparing+Mongo+DB+and+Couch+DB
>
> I was just about to send that link.
>
>> There are lots of other players in this space, too -- see
>> http://nosql-database.org/
>
> It depends on how you define "that space". There are lots of players
> in the non-relational, AKA, NoSQL space, but in the document oriented
> space I don't know of any other current contender other than MongoDB
> and CouchDB. Do you?
>
> Comparing Riak, Cassandra and MongoDB is like comparing a golf cart, a
> fork lift and a fire engine. They are just too different.
>
> But i'd say MongoDB and CouchDB belong in the same category, though
> MongoDB is optimized for performance in cluster, deployed in a single
> datacenter, with master-slave replication, and CouchDB is designed for
> easy and reliable distributed deployment with master-master
> replication among nodes that are not always online.
>
> Their conceptual data model is very similar (JSON and BSON), so it's a
> snap to migrate data from CouchDB to MongoDB (the opposite maybe more
> complicated depending on the dataset, because BSON has more primitive
> types than JSON).
>
> Where I work [1] we are doing pilot projects with CouchDB, but we also
> envision using CouchDB as the main repository for content creation,
> and pushing data to MongoDB for high demand services, if we find out
> that CouchDB can't handle the traffic.
>
> [1] http://regional.bvsalud.org/php/index.php?lang=en
>
> --
> Luciano Ramalho
> programador repentista || stand-up programmer
> Twitter: @luciano
>