Twitter uses MySQL for all their data. They forked it and made tons of improvements. Here's their blog https://blog.twitter.com/2012/mysql-twitter https://blog.

Twitter uses MySQL for all their data. They forked it and made tons of improvements. Here's their blog https://blog.twitter.com/2012/mysql-twitter https://blog.twitter.com/2012/mysql-twitter and here's the project https://github.com/twitter/mysql https://github.com/twitter/mysql