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 Deprecates cursor_sharing=similar

Oracle Database Tips by Donald BurlesonConsulting

April 25, 2015

It's well known that the setting cursor_sharing=similar has caused issues for many years.  

Oracle has always had an issue with implementing cursor peeking, a method whereby Oracle re-evaluates an execution plan to consider the value of a reentrant host variable.

 To use peeking, BOTH of the following condition must be true:

  1.  You have reentrant SQL using host variables.
  2.  The referenced column is heavily skewed, such that value of the host variable would influence the optimizer choice of execution  plan.  

This is a very rare case, such as a host variable with a highly skewed value, such that one host variable would have the "best" explain plan with a full-table scan while a more unpopular host variable value would be "best" with an index scan.  

Starting with 11g, Oracle implemented a  more intelligent solution to this rare case with the adaptive cursor sharing method to handle these rare cases, making cursor_sharing=similar obsolete.  

Oracle has decided to deprecate cursor_sharing=similar, a smart move since the overhead of peeking into a bind variable is more expensive than the unnecessary invocation of a full-table scan for a super-popular bind variable value.

 The My Oracle Support Community (MOSC) as announced the depreciation of the cursor_sharing=similar setting, per MOSC Note 1169017.1 titled Deprecating the cursor_sharing = 'SIMILAR' setting:

"We recommend that customers discontinue setting cursor_sharing = SIMILAR due to the many problematic situations customers have experienced using it.  

The ability to set this will be removed in version 12 of the Oracle Database (the settings of EXACT and FORCE will remain available).  

Instead, we recommend the use of Adaptive Cursor Sharing in 11g."

 
Get the Complete
Oracle SQL Tuning Information 

The landmark book "Advanced Oracle SQL Tuning  The Definitive Reference"  is filled with valuable information on Oracle SQL Tuning. This book includes scripts and tools to hypercharge Oracle 11g performance and you can buy it for 30% off directly from the publisher.

 


 

 

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 -  2016

All rights reserved by Burleson

Oracle ® is the registered trademark of Oracle Corporation.


 

��  
 
 
Oracle Training at Sea
 
 
 
 
oracle dba poster
 

 
Follow us on Twitter 
 
Oracle performance tuning software 
 
Oracle Linux poster