Tie::DB_FileLock extends DB_File, providing a locking layer using
flock().

Unlike Tie::DB_Lock, Tie::DB_FileLock does not duplicate files to
allow concurrent access for readers and writers.  Tie::DB_FileLock
is therefore suitable for large dbms with relatively short locking
periods.

WWW: http://search.cpan.org/dist/Tie-DB_FileLock/