cdb is a fast, reliable, lightweight package for creating and reading
constant databases. Its database structure provides several features:

* Fast lookups: A successful lookup in a large database normally takes
just two disk accesses. An unsuccessful lookup takes only one.

* Low overhead: A database uses 2048 bytes, plus 24 bytes per record,
plus the space for keys and data.

* No random limits: cdb can handle any database up to 4 gigabytes. There
are no other restrictions; records don't even have to fit into memory.
Databases are stored in a machine-independent format.

* Fast atomic database replacement: cdbmake can rewrite an entire
database two orders of magnitude faster than other hashing packages.

* Fast database dumps: cdbdump prints the contents of a database in
cdbmake-compatible format.

cdb is designed to be used in mission-critical applications like e-mail.
Database replacement is safe against system crashes. Readers don't have
to pause during a rewrite.

Note for developers:
    Packages that need to read cdb files should incorporate the
    necessary portions of the cdb library rather than relying on
    an external cdb library. (See WWW)

WWW: http://cr.yp.to/cdb.html