NoSQL standouts: New databases for new applications
Cassandra, CouchDB, MongoDB, Redis, Riak, Neo4J, and FlockDB reinvent the data store
Much of the complexity in the API is devoted to controlling just how quickly the cluster of nodes moves toward consistency. You can specify the speed of synchronization for columns and collections of values called supercolumns.
Getting everything running is now fairly well documented, but getting it running quickly requires a fair amount of both hardware and operating system tuning. The biggest bottleneck is the commit log. Optimizing the way that this is written to disk is the most important part of improving writes. Speeding up the extraction of data involves paying attention to the pattern of reads. Did your old, fancy database do this for you fairly automatically? Ah, don't complain. It's fun to think about the hardware and how it affects your software.
NoSQL databases: CouchDB
CouchDB stores documents, each of which is made up of a set of pairs that link key with a value. The most radical change is in the query. Instead of some basic query structure that's pretty similar to SQL, CouchDB searches for documents with two functions to map and reduce the data. One formats the document, and the other makes a decision about what to include.
I'm guessing that a solid Oracle jockey with a good knowledge of stored procedures does pretty much the same thing. Nevertheless, the map and reduce structure should be eye-opening for the basic programmer. Suddenly a client-side AJAX developer can write a fairly complicated search procedure that can encode some sophisticated logic.
There's a burgeoning community growing around CouchDB. All of the major languages now have client libraries that simplify the interaction with the database and make it possible to store your data. They don't always expose all of the power of the query function, but that's not necessary for every service. There are also companies like Couchbase that bundle CouchDB into commercial product offerings. Cloudant offers the database as a hosted service and partners with companies like CloudBees to support the code running on the Cloudant cloud. It's getting easier and easier to use CouchDB like a service.
NoSQL databases: MongoDB
Well, that's simplifying things a bit. The big difference is that MongoDB will create indices for the columns of your database and return queries faster when the indices are correctly constructed. That's part of your job, by the way. You want to anticipate which indices your users will need.
There's also a fair number of extra tools for working with the database. PHPMoAdmin, a cousin of the MySQL tool PHPMyAdmin, is just one of almost a dozen tools for admins. The proliferation of these tools is gradually erasing one of the standard reasons for sticking with a classic database. As I found more of them, I noticed that everything was more comfortable.