The Berkeley DB library has many other fascinating features
Not all are available through DB_File
For example, there is a DB_Queue file type
This is like an array
But it is optimized for push and shift operations
You might use this to store a log file
When the log file exceeds a certain size, you shift the old records off the front
There is an option to keep the values for duplicate keys in a user-defined order
It supports transactions
The BerkeleyDB module provides interfaces to this functionality
It's worth skimming through the manual
Check out http://www.sleepycat.com/docs/reftoc.html for a tutorial and overview