These functions allow you to store records stored in a dbm-style
database. This type of database (supported by the Berkeley DB,
GDBM, and some system libraries,
as well as a built-in flatfile library) stores key/value pairs
(as opposed to the full-blown records supported by relational
databases).
In order to use these functions, you must compile PHP with dbm support
by using the --with-db option. In
addition you must ensure support
for an underlying database or you can use some system libraries.