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 








  Oracle Database Tips by Donald Burleson

Using Histograms 

Histograms help optimize queries and other actions against data that is nonuniformly distributed about a mean. The common term for poorly distributed data is skewed data. In particular, in earlier versions of ORACLE7,  the cost-based optimizer would go out to lunch if you handed it skewed data. There is a cost associated with histograms, so they should be used only for badly skewed data. Histograms are static and must be periodically renewed just like table statistics.      

Histograms should not be used when:

  • All predicates on the column use bind variables.

  • The column data is uniformly distributed.

  • The column is not used in WHERE clauses of queries.

  • The column is unique and is used only in equality predicates.      

Histograms are created in "bands" of value ranges. For example, if the data in your test_result tables measurement column is skewed into six general ranges, then you would want to create six bands of history:

See Code Depot   

If you know the exact number of keys, and the value is less than 255, set the size to that value; otherwise, set it to 255. Histogram statistics are stored in the DBA_, USER_, and ALL_ HISTOGRAMS views. Additional row statistics appear in the USER_TAB_COLUMNS, ALL_TAB_COLUMNS, and DBA_TAB_COLUMNS views.

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.