The wonderful thing about key value pair databases like Couchbase is their simplicity. You don't need to fret about data models or relationships between tables. You have a unique identifier -- the key value -- that maps to an object, the contents of which the database does not concern itself. As Wiederhold explained, "it's basically set and get." You enjoy blazing performance and the ability to scale out just by adding commodity servers; if a server goes down, distributed redundancy keeps the database humming.
When it comes to scaling, an RDBMS tends to demand a beefy server that you must scale up rather than out -- in other words, you upgrade the horsepower of a single server rather than simply adding commodity servers as needed. When you run out of performance headroom on your single RDBMS server, you then have to "shard" the database across multiple servers, which incurs its own complications. Alternatively, as Andrew Oliver observes, you can opt for an RDBMS solution like Oracle RAC (Real Application Clusters), which is designed to scale out rather than up -- but Oracle RAC in particular is quite difficult for developers to write to.
As Wiederhold told me, one of the great advantages of both key value pair and document databases is that they're both more natural for developers to write to than relational RDBMSes. Wiederhold also noted that Couchbase was becoming a document database in its 2.0 release, coming in just a few weeks. The InfoWorld Test Center is already champing at the bit to review it; it will be interesting to see how it stacks up against the incumbent document database leader MongoDB, which InfoWorld's Andrew Glover reviewed last February.
Although Couchbase and MongoDB represent the sweet spot of the NoSQL market right now, there's much more -- like graph databases or columnar family databases. You could even lump in Hadoop if you like, though it applies almost entirely to analytics for semi-structured data. In fact, each NoSQL type is suited to its particular set of applications -- marking the twilight of the SQL RDBMS as a one-size-fits-all tool.
One final observation: Note that NoSQL lends itself to Web applications and, in fact, many large early customers are SaaS providers. As with many exciting new technologies today, NoSQL is helping enable the migration of technology from the corporate data center to the cloud.
This article, "The wild, crazy world of databases," originally appeared at InfoWorld.com. Read more of Eric Knorr's Modernizing IT blog. And for the latest business technology news, follow InfoWorld on Twitter.