A '''Constant Database''' (or CDB) is a database intended to be read many times but only written to once. [[Dan Bernstein]] created a constant database specification and programs to utilize it on [[Unix]] systems, refer to his [http://cr.yp.to/cdb.html his CDB page].
CDBs are very commonly used in mail systems such as [[Qmail]].
[[Michael Tokarev]] has created an implementation called [http://www.corpit.ru/mjt/tinycdb.html TinyCDB] that can be used with the [[Postfix (software)|Postfix]] MTA.