Drizzle is a re-thought and re-worked version of the MySQL kernel designed specifically for high-performance, high-concurrency environments. In this exclusive article, MySQL guru Jeremy Zawodny takes an inside look at the goals and state of Drizzle development.
If you visit the Drizzle project homepage, it explains:
Drizzle is building a database optimized for cloud and [network] applications. [Drizzle] is being designed for massive concurrency on modern multi-cpu/core architectures. The code is originally derived from MySQL.
The article continues at http://www.linux-mag.com/id/7379/