Whats the best way to use a SQL DB along side a NoSQL DB? I want 
to keep my users and other data in postgres but have some data that 
would be better suited for a NoSQL DB like redis. 

I see a lot of talk about switching to NoSQL but little talk on 
integrating it with existing systems. I think it would be foolish to 
throw the baby out with the bath water and ditch SQL all together, 
unless it makes things easier to maintain and develop. 

I'm wondering what the best approach is for relating data stored in 
SQL to my data in redis. I was thinking of something along the line of 
this.

* User object stored in SQL
* Book object in redis, key sh1 hash of value, value is a JSON string
* Relations stored in redis, key User.pk:books, value redis set of sha1's

Anyone have experience, tips, better ways?