Reality DB

"Reality sunk in and they had to move on from elegant theories to the bitterness of solving real-world problems. Whenever you hear about a new database, remember this: this shit is really, really, really hard. It typically takes many years for a database or storage engine to become production-ready in the real world.

"

http://www.xaprb.com/blog/2013/12/28/immutability-mvcc-and-garbage-collection/