Jonathan Ellis from the Cassandra project published a fantastic overview of the current NoSQL ecosystem in late 2009. He analyzed 10 popular NoSQL databases along three axes: horizontal scalability, data model and internal persistence design. It’s a great read, and still pretty much valid as of today. I stumbled upon it via Emil Eifrem from Neo4j, who adds some interesting thoughts on scaling to size vs. scaling to complexity. Obviously, scaling is easier for simple stores, but even the complex Graph DBs such as Neo4j scale well beyond what we’re used to see from the RDBMS household names Oracle, Sybase and SQL Server.