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) (click on video below)
  3. The Database ACID Test (3:09)
  4. Physical and Logical Corruption (1:37)
  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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Tutorial Agenda

Oracle Instance Recovery Tutorial


Module 2 – Tutorial Agenda


>> John:  Thank you, Dave. Good morning or good afternoon – depending on your time zone – to all of you. 


What I want to cover in our short lecture today is, in response to popular demand, we’re going back to basics once again. I want to cover some of the database fundamentals that I find is sometimes skipped over when people first study Oracle. Of course, if you study Oracle with us we don’t skip over anything. 


It’s possible for some of you this material – because this is a bit of a back to basics – is largely revision, but I hope that nonetheless you will get something out of it. I have found from years consulting in the field and a bit of time in the classroom that many DBAs, perfectly competent DBAs, fully competent production DBAs have perhaps never fully investigated what actually happens in memory and on disc when you execute DML. 




So what I intend to do is run through firstly the requirements of a relational database management system as regards to data corruption. Basically, that’s what we call the ACID test and it’s quite simply the relational database is not allowed to corrupt any data under any circumstances. We’ll explain what’s going on and of course demonstrate as well how Oracle has actually implemented this. 


Understanding this mechanism is crucial for any DBA. But in particular I want to present it in a manner that perhaps will help you explain it to others. Why? So that you can motivate the investments in Oracle technology that your organization needs. 


Oracle is expensive. I’m in love with the technology, no question about that, but we can’t deny that it is not cheap and I find that I often need to explain to users why it’s essential, what they’re getting for their money. There is, above all, this one reason. In a properly configured database, it is absolutely impossible to lose or corrupt data provided the database is properly configured and managed. 




What I want to run through today – I’ll prove – what is going on in the background to implement this and prove that the recovery mechanism in the event of any corruption is simply unavoidable.


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