I am the author of Redisql and I wrote a blog post today explaining the concepts behind Redisql (a RDBMS on top of the NOSQL datastore redis)
http://jaksprats.wordpress.com/2010/09/28/introducing-redisq...
The original idea was to have a single roof to house both relational data and redis data and both types of data would exhibit similar lookup/insert latencies under similar concurrency levels.
And then I added simple commands to convert redis data into relation tables and vice versa, and I made many memory optimisations, etc... the result hopes to be the complete datastore solution for applications that require the fastest data lookups/inserts possible