Chapter 15: Reliability and Security in Database Servers Neyha Amar CS 157B May 6, 2008

Agenda Reasons why backup and recovery are important to database servers Strategies for recovery from failures Ways in which DB systems define and enforce security control

Potential Reasons of Database Failure 1. The database server computer crashes. 2. The database server program crashes. 3. A database client computer crashes. 4. A client program crashes. 5. The network connection between client and server fails. 6. A transaction executes a rollback operation. 7. A transaction executes an illegal operation. 8. Two or more transactions deadlock. 9. One or more transactions introduce errors into the database. 10. Data on a disk drive is corrupted.

Recovery Strategies Recovery via Reprocessing:  Recover the database state from a backup and reprocess all transactions that have occurred since the backup was created  Drawback: does not guarantee durability by reprocessing, except in the most limited cases (i.e. applications that do not respond to direct user input)

Recovery Strategies (cont ’ d) Recovery via Roll Forward:  Recover database state from a backup and then reapply all changes of committed transactions in same order that they were originally committed using redo logs  Advantage: Full durability using physically remote backups and redo logs

Recovery Strategies (cont ’ d) Recovery via Rollback:  Recover to a previous correct database state by removing the effect of corrupted transactions by using undo logs  Advantage: More efficient than Rollforward when database has not crashed and only few bad transactions

Recovery Strategies (cont ’ d) Recovery from Disk Corruption:  Mostly recovery done by backup and roll forward  If some disk pages corrupted might be possible to recover from disk cache  Else, recreate corrupted pages using transaction logs

Security in Relational Database Systems Database security starts with physical security DBMS uses two main types of security:  Account security for User Authorization  Access security for Protection of Database Objects

Security in Relational Database Systems (cont ’ d) User Authorization  Database stores identifiers and passwords in system tables  Each connection by user or client program must be authenticated as a valid database user  System provides commands to create, alter, and drop users  Examples: sample SQL statements to manipulate user accounts create user Jane identified by starfish; drop user Jane;

Security in Relational Database Systems (cont ’ d) Protection of Database Objects  Database defines a collection of privileges granted to users  Access privileges restrict (and allow) access by specific users to specific operations on specific objects.  Role capability used to grant collection of privileges to many users  Examples: sample SQL statements affecting database privileges grant insert on Customer to Jane; grant select on Customer to public; create role FloorManager identified by ImInCharge; grant role John to FloorManager;

References Principles of Database Systems With Internet and Java Applications by Greg Riccardi, 2001, Addison-Wesley Database System: The Complete Book by Hector Garcia-Molina, 2002, Prentice Hall west.oracle.com/docs/cd/A87860_01/doc/server.817/a76993/back upst.htm