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 


 

 

 


 

 

 

 

 

Minimizing Table Locks to Optimize Performance

Oracle RAC Cluster Tips by Burleson Consulting

This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters.  To get immediate access to the code depot of working RAC scripts, buy it directly from the publisher and save more than 30%.

Also see these important notes on the disable table lock command.


For RAC, table locks are coordinated through global inter-instance communication. Due to the fact that properly designed applications do not need to lock entire tables, table locks can be disabled to improve locking efficiency with minimal adverse side effects. Essentially, there are two methods for disabling table locks:

* Disabling table locks for individual tables.

* Setting dml_locks to zero.

The following sections will examine these methods.

Disabling Table Locks for Individual Tables

To prevent users from acquiring individual table locks, the following statement can be used:

ALTER TABLE table_name DISABLE TABLE LOCK

When users attempt to lock tables with disabled locks, they will receive an error. To re-enable table locking after a transaction, the following statement can be used:

ALTER TABLE table_name ENABLE TABLE LOCK

Using this syntax forces all currently executing transactions to commit before enabling the table lock. The statement does not wait for new transactions to start after issuing the ENABLE statement. The disadvantage to this statement is that it must be executed for all tables that may experience improper locking.

To determine whether a table in the schema has its table lock enabled or disabled, the table_lock column in the user_tables data dictionary table should be queried. If SELECT privilege is on dba_tables, the table lock state of other user's tables can be queried as well. The all_tables views can be used to see the locking state of tables for which a user has been granted SELECT privileges.

Setting dml_locks to Zero

Using the dml_locks initialization parameter, table locks can be set for an entire instance. This will disable the DROP TABLE, CREATE INDEX and LOCK TABLE commands. If these commands are not needed, dml_locks should be set to zero to minimize lock conversions and achieve maximum performance. DDL statements cannot be executed against tables with disabled locks.

SQL*Loader checks the flag to ensure that there is not a non-parallel direct load running against the same table. The use of direct load forces Oracle to create new extents for each session.

If dml_locks are set to zero on one instance, it must be set it to zero on all instances. If non-zero values are used with the dml_locks parameter, the values need not be identical on all instances.

Performance for Object Creation in Real Application Clusters

In any Oracle database, DDL statements should be used for maintenance tasks, not during normal system operations. For example, global temporary tables or PL/SQL tables should be used rather than permanent tables for reports. If this guideline is followed, in most systems, the frequency of DDL statements should be low.

If the application has to create objects frequently, performance degradation to the RAC environment will occur. This is due to the fact that object creation requires inter-instance coordination. A large ratio of dlm_conflicts to dlm_requests on the dc_object_ids row cache in v$rowcache, the same SELECT as was used for sequences will work here as well, along with excessive wait times for the row cache lock event in v$system_event, is indicative that multiple instances in the cluster are issuing excessive amounts of concurrent DDL statements.

About the only method to improve object creation performance in these situations is to set event 10297 so that it caches object_id values. This will improve concurrent object creation by eliminating the recursive DDL and some of the intra-instance pinging. To set event 10297, the following line can be added to the initialization parameter file:

event="10297 trace name context forever, level 1"

If the additional level argument is set to one, the caching behavior is automatically adjustable internally. Otherwise, the level can be set to the desired cache size.

 


This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters, Rampant TechPress, by Mike Ault and Madhu Tumma.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.

http://www.rampant-books.com/book_2004_1_10g_grid.htm


 

 
��  
 
 
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