They don’t teach you this in college, but the fundamental theorem of the software industry is the idea that everything needs to be rewritten all the time. As a corollary, web startup engineers believe that there is no problem but scalability, and architecture is its solution. And thus, the NoSQL movement was born.

The idea is that object relational databases like MySQL and PostgreSQL have lapsed their useful lifetimes, and that document-based or schemaless databases are the wave of the future. Never mind of course that MySQL was the perfect solution to everything a few years ago when Ruby on Rails was flashing in the pan. Never mind that real businesses track all of their data in SQL databases that scale just fine. (For Silicon Valley readers, Walmart is a real business, Twitter is not.)

Invariably, all web projects start off with something like Rails or Django, most likely backed by MySQL. The data relationships are easy to model, and the application works well. If you are lucky enough that people actually use your application, eventually you will start to see some performance issues. At this point, a developer who values technological purity over gettin’ shit done will advocate “rewriting the whole thing in a weekend using Cassandra”. And if he’s smart enough, he might just pull it off. (Of course, said developer has only migrated the app to use a different data store – all of the ancillary support code was conveniently ignored) (更多…)