Transaction Processing: Concepts and Techniques. Jim Gray and Andreas Reuter. Morgan Kaufman, 1992.
One of the most informative and readable computer texts around. If something about transactions is not covered here, maybe it doesn't exist!
An Introduction to Database Systems, Volumes I and II. C.J. Date. Addison-Wesley, 1994.
A thorough treatment of persistence issues and database technology.
DBI web site by Alligator Descartes: http://www.symbolstone.org/technology/perl/DBI/.