Uh... ever thought of picking up a book? I don't think that anyone could just whip up a post describing databases to the detail that you requested. I mean, distributed databases and concurrency control is a complicated issue that has teams of software engineers working on it full-time, at places like IBM for their DB2 product, Oracle, Sybase, etc.
You should either enroll in a database systems administration class or three at your nearby community college or university extension program, or go to a technical bookstore and look through their databases aisle.
I just searched on amazon for "database theory" and "database concurrency" and got hundreds of hits. For example:
You probably don't even have to BUY these books, you can probably check them out from a local library, especially one on a college/university campus.