Check this interesting and useful post of Ken Delong; about Horizontal database partitioning with Spring and hibernate and the situation which he had used this. I think this article is good to identify the use of horizontal database partitioning. Being a Developer who is very much interested to learn more about the Project Architecture, design patterns and how people Handled the complex situations in the big projects, this article gave me some good knowledge. It also discuss about Hibernate Shrads too.
Thoughts on Software Development Trends, Enterprise Architecture, Design, Big Data, and Cloud Computing.
Orange Slate 
That’s an intelleignt answer to a difficult question xxx