According to Ryan King, a software engineer at Twitter, the MySQL database used in Twitter is going to be replaced by the open source Cassandra data management system. Cassandra is a new types of data handling systems that are powering large Web applications, particularly social networking sites which deal with hundreds of thousands or millions of users. It can run on large server clusters and is capable of taking in very large amounts of data at a time, performing sorts and calling up relevant data quickly.

This move by Twitter to stop using MySQL is just one of several recent MySQL replacements at social networking sites. Other websites like Facebook and Digg, which were also powered by MySQL, have already made the switch.

Twitter has gone from 2 millions tweets a day to more than 50 million in 2009. King is quoted in an interview as saying that Twitter wanted a system that could keep up with such kind of growth. King also said in the interview that Twitter sought a system with no single point of failure, which could execute highly scalable writes, and had a healthy open source community behind it.

Cassandra was originally created by Facebook to manage its data. It is now an Apache Software Foundation project and has recently been given a full project status and has an active developer group.

Since big Web systems need to assimilate large masses of data and make it available, frequently in read only fashion, systems like Cassandra concentrate on more immediate goals than the pristine data handling rules of relational systems.

More machines can be added to a cluster running Cassandra without disrupting its operation. Cassandra can expand without application programmer intervention across the server cluster. As more hardware are brought on line   Cassandra can activate itself on a new node, calling out to the cluster load balancer for work to do.

[via Information Week]