Oracle Database Instance Recovery Tutorial

Is It Possible to Corrupt an Oracle Database?

No, You Cannot – Not If It Is Properly Administered

Why? Because the mechanism of redo and undo is the best yet developed on this planet.

In this tutorial, Oracle Certified Master John Watson will explain redo, undo, commit, instance recovery and demonstrate why your database can never lose one row of committed data.

Learn what actually happens, in memory and on disc, when DML is issued. John will demonstrate that instance recovery is automatic, and unstoppable.

This is critical and essential knowledge for all Oracle Administrators and DBA students.

Presenter: John Watson, Oracle Certified Master

This free tutorial is segmented into fourteen separate lessons:

  1. Introduction to Oracle Certified Master John Watson and SkillBuilders (1:44)
  2. Tutorial Agenda (2:40)
  3. The Database ACID Test (3:09)
  4. Physical and Logical Corruption (1:37) (click on video below)
  5. Demonstration – What Does Oracle do when DML is Executed? (9:47)
  6. Commit and the Log File Sync Wait Event (1:18)
  7. When Why and How Does Oracle Write to Disk (1:58)
  8. What About Checkpoints? (1:16)
  9. Discussion about COMMIT NOWAIT (3:46)
  10. Lecture – What Oracle Database does when DML is Executed (7:22)
  11. The Oracle Instant Crash Recovery Mechanism (6:24)
  12. Principles to Remember (0:52)
  13. Oracle – The Incorruptible Database (1:54)
  14. Next Steps (0:47)

Date: Jun 4, 2013

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Physical and Logical Corruption

Oracle Instance Recovery Tutorial


Module 4 – Physical and Logical Corruption


>> Dave:  What about corruption caused by physical damage?


>> John:  Corruption caused by physical damage, that’s out of the DBA’s and Oracle’s control. That physical damage, we can guarantee zero loss of data provided the database is properly configured in terms of archivelog mode backup, Data Guard even, but the recovery from physical damage is not going to be automatic. So we guarantee it, but it isn’t automatic.




>> Dave:  Guaranteed as long as we’ve done proper administration with backups?


>> John:  And if we haven’t, you fire your DBA. That’s usually the management’s immediate reaction to an Oracle database losing data.




>> Dave:  Very good. One more question. What about logical corruption or bad block formats?


>> John:  Logical corruption again is out of Oracle’s control. But from release 11g we can in fact repair logical corruption automatically but only if you are in the Data Guard’s environment with active Data Guard configured. That’s really a bit out of scope for the database. It’s damaged beyond the database’s control but we can in fact repair that automatically through the active Data Guard mechanism. If a logically corrupted block is detected in the primary database, it will be restored and recovered using a block from the standby database and the other way around as well.


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