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 








Disabling hash joins

Oracle Database Tips by Donald Burleson

Disabling hash joins

Tropashko notes that the hash joins may not be the fastest table join method and he removes them  by unsetting the hash_join_enabled parameter and reviews the resulting nested loops table join method:

alter session set "_hash_join_enabled" = false;

You can also turn off hash joins at the session level with "alter session set HASH_JOIN_ENABLED = FALSE"

You can influence the type of join your query will do using the USE_NL (Nested Loop), USE_MERGE (Sort-Merge), and USE_HASH (Hash join) hints.

Many times these are accompanied by the use of the LEADING or ORDERED hint in order to let Oracle know the optimal join order.

The particular query that we are studying in this section has 5 query blocks: 2 pairs of selects from the tables A and B, and one set operation. After this query is transformed, it would consist of only 3 query blocks which we might witness from the QBLOCK_NAME column of the PLAN_TABLE.

Execution plan for comparing the contents of two tables  with hash joins disabled

For more on advanced disabling of hash joins, see Vadim Tropashko's  book "SQL Design Patterns: The Expert Guide to SQL Programming"

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.



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.