I don't know about Rails (It's DB library is ActiveRecord, if I recall names correctly) but SQLAlchemy which is Python's big ORM, has support in it for sharding

I don't know about Rails (It's DB library is ActiveRecord, if I recall names correctly) but SQLAlchemy which is Python's big ORM, has support in it for sharding and similar partitioning, etc. When we built sketchcast.com sharding was on the design list and a concern - there were some fantastic articles at http://highscalability.com/ http://highscalability.com/ that we used as a basis for some of our design.