PureDB is a portable and tiny set of libraries for creating and reading
constant databases. It manages data files that contains text or binary
key/data pairs of arbitrary sizes. Lookups are very fast (normally only one
disk access to match a hash value), overhead is low (a database is 1028
bytes plus only 16 extra bytes per record), multiple concurrent read access
are supported, and databases can be up to 4 Gb long, and they are portable
across architectures. 

WWW: http://pureftpd.sourceforge.net/puredb/