Call now: 252-767-6166  
Oracle Training Oracle Support Development Oracle Apps

 E-mail Us
 Oracle Articles
New Oracle Articles

 Oracle Training
 Oracle Tips

 Oracle Forum
 Class Catalog

 Remote DBA
 Oracle Tuning
 Emergency 911
 RAC Support
 Apps Support
 Oracle Support

 SQL Tuning

 Oracle UNIX
 Oracle Linux
 Remote s
 Remote plans
 Application Server

 Oracle Forms
 Oracle Portal
 App Upgrades
 SQL Server
 Oracle Concepts
 Software Support

 Remote S


 Consulting Staff
 Consulting Prices
 Help Wanted!


 Oracle Posters
 Oracle Books

 Oracle Scripts

Don Burleson Blog 








Internals of Oracle redo log management

Oracle Tips by Burleson Consulting


Also, see these important notes on redo log buffer sizing.

I recently had a DBA with an interesting question about why there appears to be redo log images generated after an SQL ?select? statement.  Normally, we are taught that redo is only for DML changes (insert, update, delete), but the explanations for this may be surprising. 

  • Queuing up messages and emailing them

  • Internal system-level redo

The most important of the system-level redo is the "delayed block cleanout" mechanism that will generate redo on a select statement, and it is visible through the statistics


  • "cleanouts only - consistent read gets"

  • "cleanouts and rollbacks - consistent read gets"


Redo with a select statement happens when dirty blocks get written to the database, and are then "cleaned up" when next read of that data block. This could happen when a large DML statement does not commit before the DB Writer needs to write modified blocks to disk.  The next time the blocks are read by a select statement they get modified, hence REDO is generated by the select statement.


Special thanks to Oracle guru David Aldridge for this Oracle tip!



Oracle Training at Sea
oracle dba poster

Follow us on Twitter 
Oracle performance tuning software 
Oracle Linux poster


Burleson is the American Team

Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

Verify experience! Anyone considering using the services of an Oracle support expert should independently investigate their credentials and experience, and not rely on advertisements and self-proclaimed expertise. All legitimate Oracle experts publish their Oracle qualifications.

Errata?  Oracle technology is changing and we strive to update our BC Oracle support information.  If you find an error or have a suggestion for improving our content, we would appreciate your feedback.  Just  e-mail:  

and include the URL for the page.


Burleson Consulting

The Oracle of Database Support

Oracle Performance Tuning

Remote DBA Services


Copyright © 1996 -  2020

All rights reserved by Burleson

Oracle ® is the registered trademark of Oracle Corporation.