Does anyone know what is the actual underlying database on Graphcool? It cannot be a secret anymore as you can run it yourself. But I cannot find any info about it in the docs.

It's AWS Aurora, or MySQL locally

For future reference: https://graph-cool.netlify.com/docs/faq/graphcool-technology-ul6ue9gait/

I was looking for that - it doesn't seem to have been copied into the new docs though

Yeah - docs seem to be all over the place at the moment