Things like MySQL and PHP have bad reputation nowadays but Facebook shows impressive use cases and improves the technology more and more.
While tools like MySQL and PHP aren't as bad as the community makes them out to be - Facebook is a terrible example how "impressive" these tools can be considering that Facebook almost entirely rewrote both of those tools (https://github.com/webscalesql/webscalesql-5.6, https://github.com/facebook/hhvm)