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)
  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) (click on video below)
  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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What About Checkpoints?

Oracle Instance Recovery Tutorial


Module 8 – What About Checkpoints


>> Dave:  What happens when automatic checkpoint occurs? Automatic checkpoint happens every 3 seconds I think?


>> John:  No, no, no, no, no, no, no. The full checkpoint – I should’ve been a lot tighter in my terminology here. Full checkpoints never occur unless you ask for them with alter system checkpoints or clean shutdown. When you do a shutdown immediate or shutdown normal, it will get a full checkpoint. My terminology was loose here. 




Partial checkpoints occur automatically on demand. For instance, you’ll get datafile checkpoints whenever you put a tablespace in the backup mode or whenever RMAN begins to back up a data file. 


There were a number of reasons for partial checkpoints but the other reasons of 3 seconds or space needed in the buffer cache, that’s only going to be writing a very few buffers. Some people refers – this is the incremental checkpoint. It pushes the checkpoint position forward slowly.


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