cdb 是一个快速、可靠而且简单的包，用来创建和读取不变的数据库，数据库结构提供多种特性：
快速查找: A successful lookup in a large database normally takes just two disk accesses. An unsuccessful lookup takes only one.
低负载: A database uses 2048 bytes, plus 24 bytes per record, plus the space for keys and data.
无随机限制: 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.
快速原子的数据库替换: 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 设计用于关键任务的应用，例如 email。
