cdb is a fast, reliable, simple 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.
