In this article over at Database Journal they explain how to de-fragment your mysql database. If you are like me you don't normally think about anything but file systems getting fragmented. It seems from this article that for very similar reasons Databases get fragmented and should have the white space in the compressed out just like on a file system. They same types of performance benifits can also be found when doing this.
We have been hearing a lot about NoSQL databases over the last couple of years. If you are curious about what the good and bad things about them who better to ask than the nice folks over at Database Journal. They wrote a great article that should help you get started on your path to determinng whether NoSQL databases are right for your next project. There were several other links on the page pointing to deeper discussions on the topic of NoSQL databases. It's a very balanced and well thought out article worth the time to read.