WebScaleSQL is a collaboration among engineers from several companies that face similar challenges in running MySQL at scale, and seek greater performance from a database technology tailored for their needs.
Those “several companies” are Facebook, Google, LinkedIn, and Twitter. And the collaboration mentioned is a true collaboration:
For example, to introduce a code change, a WebScaleSQL engineer can propose a change. Then a WebScaleSQL engineer from another company will review the code and provide feedback. If both engineers agree the change makes sense and is functional, it will be pushed into the WebScaleSQL branch for everyone to use.
The engineers over at Facebook have posted a list of improvements that have already made it into WebScaleSQL.