[bryanrasmussen]

I'm betting Facebook uses a lot of different types of databases.

[randomdata]

No doubt, but the core product known for being graph-y is based on MySQL.

Indeed, there is a graph data store (TAO) built on top of that base, but as we're talking about databases...

[jiggawatts]

Many graph databases are relational "under the hood". The graph part is often just a specialised index.

[randomdata]

Just as Facebook uses MyRocksDB (a KV store) underneath MySQL. There is a definite turtles all the way down.

But where do you draw the line? Is your Ruby on Rails CRUD app that exchanges JSON documents a document database? Fundamentally, what's the difference between said Rails app and TAO, aside from one being centred around documents and the other graphs?

Surely "base" is meant to be more specific?