1. Dealing with Database Corruption DBA 911

2. Who am I? 2 David M Maxwell twitter.com/dmmaxwell or twitter.com/upsearchsqltwitter.com/dmmaxwelltwitter.com/upsearchsql dmmaxwell@gmail.com or david.maxwell@upsearch.comdmmaxwell@gmail.comdavid.maxwell@upsearch.com dmmaxwell.wordpress.com or upsearch.comdmmaxwell.wordpress.comupsearch.com –Scripts / Slides available here. Visit https://upsearch.com/connect-with-us/ and find your ideal way to stay in touch.https://upsearch.com/connect-with-us/

3. Agenda Definitions of Consistency and Corruption Planning and Practicing Errors to Watch For Sample Corruption Scenarios 3

4. What are Consistency and Corruption? Consistency is an ACID property of transactions. –ACID = Atomic, Consistent, Isolated, Durable –Consistent = Transactions must follow rules. Corruption is the loss of Consistency. Almost always an IO subsystem problem. Occasionally a software error. May be delayed, but not prevented. 4

5. Planning for Corruption Determine the appropriate SLA – then exceed it. Monitor for corruption with Agent jobs and alerts. Document and test your plan. –Consider multiple paths to restoring service. Test your backups. Practice regularly. 5

6. Corruption Situations in Practice Don’t panic. Communicate appropriately. Run CHECKDB – and let it finish. Examine all the output carefully. Take your plan one step at a time. Document everything. 6

7. Errors to Watch For 823 – Read Failure 824 – Page Checksum Failure –Requires CHECKSUM page verification. 825 – Read Retry –Logged as a Severity 10 error. Won’t be caught by most systems. 833 – In-Memory Checksum Failure –Far worse than Error 824. 2750 – Data Purity Error –Value stored is outside the range of the datatype. –SQL Server cannot repair this. 7

8. Demonstrations DBCC Commands Data Purity Error Nonclustered Index Corruption Single Page Repair via Restore Repair with Data Loss 8

9. Resources SQL Server Books Online: CHECKDB –http://technet.microsoft.com/en-us/library/ms176064.aspxhttp://technet.microsoft.com/en-us/library/ms176064.aspx Paul Randal’s Blog –http://www.sqlskills.com/blogs/paul/category/checkdb- from-every-angle/http://www.sqlskills.com/blogs/paul/category/checkdb- from-every-angle/ Ola Hallengren Maintenance Procs –http://ola.hallengren.com/http://ola.hallengren.com/ Minionware: Minion CHECKDB –Currently in Open Beta Emergency Mode Repair Playtime –http://dmmaxwell.wordpress.com/2012/11/06/emergency- mode-repair-playtime/http://dmmaxwell.wordpress.com/2012/11/06/emergency- mode-repair-playtime/ 9

10. Thanks! David M Maxwell twitter.com/dmmaxwell or twitter.com/upsearchsqltwitter.com/dmmaxwelltwitter.com/upsearchsql dmmaxwell@gmail.com or david.maxwell@upsearch.comdmmaxwell@gmail.comdavid.maxwell@upsearch.com dmmaxwell.wordpress.com or upsearch.comdmmaxwell.wordpress.comupsearch.com –Scripts / Slides available here. Visit https://upsearch.com/connect-with-us/ and find your ideal way to stay in touch.https://upsearch.com/connect-with-us/ 10