1. Database Recovery Lucas Finger

2. Overview Purpose of Recovery What Causes Database Failure? Being Prepared Techniques for Recovery

3. Purpose of Database Recovery To bring the database into the last consistent state, which existed prior to the failure. To preserve transaction properties: Atomicity Atomicity Consistency Consistency Isolation Isolation Durability Durability

4. What Causes Database Failure? DB server computer or program crashes DB client computer or program crashes Network failure between client and server Data on a disk drive is corrupted A transaction executes an illegal operation Two or more transactions deadlock Transactions introduce errors into the DB

5. Being Prepared Planning ahead is the most important aspect of data recovery. What to think about: How much can you afford to lose? How much can you afford to lose? How and where backups are stored How and where backups are stored Having a written plan Having a written plan Make sure it works! Make sure it works!

6. Recovery Strategies Redundancy is the key to recovery Tools: Backups, checkpoints, and transaction logs Backups, checkpoints, and transaction logs CountTransactionLastNextActionData ItemBeforeAfter 1T102Begin 2T114WXX=100X=200 3T209Begin 4T125WYY=50Y=100 5T147RMM=200 6T308RNN=400 7T15nullEnd

7. Recovery Strategies Types of Transaction Logs Redo Log Redo Log List of all changes in the order they were committed ‘recovery and roll forward’ Mostly used for catastrophic failures Undo Log Undo Log List of all changes in reverse order ‘roll back’ Often more efficient than recovery and roll forward

8. Conclusion Data recovery is important in managing a database system. Having a good plan will help make a quick and successful recovery from a failure. Backups and checkpoints together with transaction logs help ensure your data is safe.

9. References Kumar, Vijay, and Meichun Hsu. Recovery Mechanisms in Database Systems. New Jersey: Prentice Hall, 1998. 6-50. Riccardi, Greg. Principles of Database Systems with Internet and Java Applications. Boston: Wesley Publishing, 2001. 386-391. Wynkoop, Stephen. “Data Recovery Best Practices.” Lumingent. 16 Dec 2004. Wynkoop, Stephen. “Data Recovery Best Practices.” Lumingent. 16 Dec 2004.

10. QUESTIONS?