Watched out MySQL. MongoDB is here and it is after your blogs. If you have not heard of it yet MongoDB is is an open source, scalable, high-performance, schema-free, document-oriented database. What MongoDB is designed for is problems without heavy transactional requirements that aren't easily solved by traditional RDBMSs, including problems that require databases to span many servers. What this means is MongoDB does not have a table structure like MySQL. You do not have to design your database schema before
Now I do not think every web app is going to run out and refractor all of there code for MongoDB, but maybe they should :) What Mongodb does is try to fill that void in RDBSM of sharing large amount of data between servers and accessing it quickly. Now why do I think MongoDB is going to start pushing MySQL out of the way? It is because of this. MySQL has had some notable shortcomings when dealing with scale. Now when it comes to blogs where there are lots of reads and with large blogs and websites millions of reads MySQL falls short on scaling. Here is a nice niche for MongoDB. Now Joe Shmoe's blog my not see any benefit from switching to a MonogDB backend but larger scale sites will.
MonogoDB is also about infrastructre. Where you may not end up using MongoDB for your CMS. If you a developing the next best web site hosting like Harmony then MongoDB makes a lot of sense. For me when it came to development time with Quicklogs, MongoDB crushed MySQL. Forget ALTER TABLE commands whenever you want to update your schema. MongoDB is schema free meaning you can write the schema to how you see fit. This is great for development, prototyping and upgrades down the road. The other infrasctructure play is replication and sharding. Although sharding will not be in the production deployment until 1.6, eta July 2010. MongoDB is very easy to replicate, do a initial sync and stay synced. MySQL replication in my experience has had a problem keep up with large data sets.
How is MongoDB going to push MySQL out of the way? At first I thought it was going to happen slowly, but then I watch as some big names keep showing up on the MongoDB's production deployment site and it may happen a lot sooner than I thought. Once you see a major CMS like Wordpress or Drupal port to MongoDB then it is all over. I use Wordpress and Drupal as examples because they are a couple of the most visible MySQL based app out there right now, but a new comer could easily come in a generate big time buzz. Keep an eye out for Quicklogs as one of those.
Then there is the geek build it factor. As a computer enthusiast is it just fun to use something new like MongoDB. There is also the Oracle factor. What is Oracle going to do with MySQL? Is Larry Ellison going to wake up one morning drip and a MySQL book get pissed and kill it? Probably not but that thought is always out there. The bigger question is why is Oracle still keeping MySQL around?