What database is Facebook using?

Excuse me, could you please elaborate on the database that Facebook is currently utilizing? As a platform that handles vast amounts of data on a daily basis, I'm curious to know what kind of database architecture they've chosen to support their operations. Is it a relational database, a NoSQL database, or perhaps a hybrid of both? I'm also interested in knowing if they've made any recent changes to their database system, and if so, what motivated those changes.