Write-Ahead Log Protocol Database security is concerned with protecting a database against accidental or intentional loss, destruction, or misuse. A comprehensive data security plan will address all of these potential threats, partly through the establishment of views, authorization rules, user-defined procedures, and encryption procedures. DBMS software provides security control through facilities such as user views, authorization rules, encryption, and authentication schemes. Set of security mechanisms presented in this chapter includes user with password and complete authorization, encryption of data. Database recovery procedures are required to restore a database quickly after loss or damage. Basic recovery facilities that should be in place include backup facilities, checkpoint facilities, and a recovery manager. Since the organization depends so heavily on its database, the database management system must provide mechanisms for restoring a database quickly and accurately after loss or damage. In this chapter the concept of crash recovery was presented in a lucid manner. ARIES recovery algorithm was illustrated with example in this chapter.