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) (click on video below)
  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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Transcript

Commit and the Log File Sync Wait Event

Oracle Instance Recovery Tutorial

 

Module 6 – Commit and the Log File Sync Wait Event

 

>> Dave:  Isn’t the commit the log file sync wait event and what can we do about that? Apparently one of our students just had a problem with that.

 

>> John:  Yes. The commit is exactly the log file sync wait event. When we issue the commit – it’s actually on the slide right here. You’re a bit ahead of where you are, about three minutes, 30 seconds.

 

When does log writer write? On the commit and other things, when you issue a commit your session hangs until the log writer has written all changed vectors in the buffer to disc. That is reported as the log file sync wait event as well as the ultimate bottlenecks in the Oracle system. If your database is hanging on that event, what can you do? Very, very little except perhaps there may be a couple of parameters you can fiddle around with. But in general, if that really is what’s bottlenecking your system, your only real option is to go to RAC because in the RAC environment multiple log writers multiple log buffers multiple threads of redo.

 

 

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