What is the implementation of KV?

I was wondering, which database storage is used behind the scenes for the KV store? Is it Cassandra?

Please see this thread which has comments from CF employees:

To answer your question, it’s separate from Quicksilver.

Thanks, that was an interesting read (both the blog and the thread).

I wonder why is CF implementing its own database when there are so many tried and tested lying around. Maybe because those aren’t written in Javascript so it’s difficult to run them as Workers?