Hypertable

[malthe]

Here's a system that could probably work for us as a storage.

"Hypertable is a high performance, open source, massively scalable database modeled after Bigtable, Google's proprietary, massively scalable database."

  - http://hypertable.com/

Importantly, the system keeps a configurable number of row revisions which means you can fetch non-current data, at least to the extent of providing transactional isolation.

It is not fully-versioned (revisions are timestamps). I actually haven't found any existing system that provides this.