There is a white paper available at www.syware.com/datasync/dl_wp.htm - it's a bit product specific but not too bad.

You can find a good description and plenty of problem descriptions in Database Systems, A practical Approach.... Connolly, Begg, Strachan (Addison-Wesley) ISBN 0-201-42277-8. It has a large section on concurrency control and distributed database systems.

(I'm not connected to any of the above firms/authors)