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

 
 Home
 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
 Analysis
 Design
 Implementation
 Oracle Support


 SQL Tuning
 Security

 Oracle UNIX
 Oracle Linux
 Monitoring
 Remote s
upport
 Remote plans
 Remote
services
 Application Server

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

 Remote S
upport  
 Development  

 Implementation


 Consulting Staff
 Consulting Prices
 Help Wanted!

 


 Oracle Posters
 Oracle Books

 Oracle Scripts
 Ion
 Excel-DB  

Don Burleson Blog 


 

 

 


 

 

 

 

 

Oracle index rebuilding: rebuild indexes



Oracle Database Tips by Donald Burleson

Important update:  The rules for identification of candidates for index rebuilding are always changing.  Please see my updated notes on index rebuilding.


How rare are "bad" indexes? 

 

You cannot generalize to say that index rebuilding for performance is rare, or even medium rare, it depends on many factors, most importantly the characteristics of the application.

  • In scientific applications (clinical, laboratory) where large datasets are added and removed, the need to rebuild indexes is "common".

  • Conversely, in system that never update or delete rows, index rebuilding rarely improves performance.

  • In systems that do batch DML jobs, index rebuilding "often" improves SQL performance.

There is a lot of research into the benefits of rebuilding Oracle indexes, and quite a bit of theories and rules for periodic rebuilding of Oracle indexes.  Boris Milrud has published a set of rules for when to rebuild Oracle indexes.

There are many myths and legends surrounding the use of Oracle indexes, especially the ongoing passionate debate about rebuilding of indexes for improving performance. Some experts claim that periodic rebuilding of Oracle b-tree indexes greatly improves space usage and access speed, while other experts maintain that Oracle indexes should "rarely" be rebuilt.

Oracle reports that the new Oracle10g Automatic Maintenance Tasks (AMT) will automatically detect indexes that are in need of re-building. Here are the pros and cons of this highly emotional issue:

In an OracleWorld 2003 presentation titled Oracle Database 10 g: The Self-Managing Database by Sushil Kumar of Oracle Corporation, Kumar states that the Automatic Maintenance Tasks (AMT) Oracle10g feature will automatically detect and rebuild sub-optimal indexes.

"AWR provides the Oracle Database 10g a very good 'knowledge' of how it is being used. By analyzing the information stored in AWR, the database can identify the need of performing routine maintenance tasks, such as optimizer statistics refresh, rebuilding indexes, etc.

The Automated Maintenance Tasks infrastructure enables the Oracle Database to automatically perform those operations."

Tapio Lahdenmaki and Michael Leach note in their outstanding book on SQL optimizers "Relational Database Index Design and the Optimizers" that:
"While the placebo theory is hard to deny, we believe that there are many indexes in the world that should be reorganized (rebuilt) periodically to realize the full benefit of fast sequential read.Many indexes grow; some indexes start with a volatile and ever-increasing column."

When can we "prove" a benefit from an index rebuild?  Here, Robin Schumacher proves that an index that is rebuilt in a larger tablespace will contain more index entries by block, and have a flatter structure:

"As you can see, the amount of logical reads has been reduced in half simply by using the new 16K tablespace and accompanying 16K data cache."

In an OracleWorld 2003 presentation titled "Oracle Database 10g: The Self-Managing Database" by Sushil Kumar of Oracle Corporation, Kumar states that the new Automatic Maintenance Tasks (AMT) Oracle10g feature will "automatically detect and re-build sub-optimal indexes."

This shows the Oracle segment advisor recommending a rebuild of an index: 

"The page lists all the segments (table, index, and so on) that constitute the object under review. The default view ("View Segments Recommended to Shrink") lists any segments that have free space you can reclaim."


Oracle index rebuild advisor (Source: Oracle Corporation)

See my related notes on index rebuilding:

 


 

 

��  
 
 
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 -  2017

All rights reserved by Burleson

Oracle ® is the registered trademark of Oracle Corporation.

Remote Emergency Support provided by Conversational