Versions of BerkeleyDB >= 3.0 have table and record level locks builtin. I have just started looking into them my self but you may want to check out Apache::Session::BerkeleyDB and specifically Apache::Session::Lock::BerkeleyDB and of course BerkeleyDB.

The perl documentation for BerkeleyDB is lacking so you will probably have to have a look at the C API at http://www.sleepycat.com.

perrin has a great article on perl.com that mentions some of the issues of using BerkeleyDB locking here

-Lee

"To be civilized is to deny one's nature."