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 


 

 

 


 

 

 

 

 

undo_management parameter Tips

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%.


The initialization parameters shown in Table 8.6 are relevant for undo management.

PARAMETER

DESCRIPTION

undo_management

If AUTO, use automatic undo management mode. If MANUAL, use manual undo management mode.

undo_tablespace

A dynamic parameter specifying the name of an undo tablespace to use.

undo_retention

A dynamic parameter specifying the length of time to retain undo. Default is 900 seconds.

undo_suppress_errors

Set to TRUE to suppress error messages generated by manual undo SQL statements when operating in automatic undo management mode. If set to FALSE, error messages are issued. This is a dynamic parameter.

Table 8.6: Undo Initialization Parameters

To view the existing parameters, use the command:

SQL>  show parameter undo

NAME                             TYPE        VALUE
-------------------------------- ----------- ----------
undo_management                  string      AUTO
undo_retention                   integer     900
undo_suppress_errors             boolean     FALSE
undo_tablespace                  string      UNDOTBS1  
                  

UNDO Tablespace Features

Some of the general features of undo tablespaces include:

* They are locally managed with system extent allocation.

* The UNDO tablespace cannot be used for any purpose other than UNDO segments and no operations can be performed on system-generated undo segments. When trying to create a table using the following statement:

create table salesman(
   name varchar2(4),
   salesid number(6) )
tablespace
   undo_rbs1 ;

The following message will be generated: ORA-30022: Cannot create segments in undo tablespace

* Only one UNDO tablespace can be used at the instance level.

* UNDO segments are created automatically and are owned by PUBLIC. They are named as _syssmun$ and are not manually manageable. The number of segments depends on the sessions parameter.

* When Automatic undo management (AUM) is chosen, it will not be possible to manage an undo or rollback.

For example, if this statement is issued:

create public rollback segment rsg1 tablespace rbs1 ;

The following error will be generated: ORA-30019: Illegal rollback segment operation in automatic mode

* Only the undo segments of the active UNDO tablespace and the SYSTEM rollback segments are kept online.

* All the instances in RAC must run in the same undo mode (i.e. AUTO or MANUAL).

Table 8.7 shows the views that provide undo information.

VIEW

DESCRIPTION

v$undostat

Contains statistics for monitoring and tuning undo space. Use this view to help estimate the amount of undo space required for the current workload.

v$rollstat

For automatic undo management mode, information reflects behavior of the undo segments in the undo tablespace.

v$transaction

Contains undo segment information.

dba_undo_extents

Shows the commit time for each extent in the undo.

Table 8.7: Dynamic performance views related to undo

System Rollback Segment

The system rollback segment is shared, and is used by all instances for transactions involving system objects. Even when using the automatic undo management method, Oracle can still use the system rollback segment. There is only one system rollback segment for the entire database. It resides in the SYSTEM tablespace.

Using Rollback Segments ? Manual Method

Even though the recommended method is to use automatic undo management (AUM), the traditional method of manually creating rollback segments is allowed. In such a case, set the initialization parameter undo_management=MANUAL. When operating in manual mode, each instance needs at least one rollback segment to start successfully.

A rollback segment may be acquired by only one instance. Once an instance acquires a particular rollback segment, it is used exclusively by that instance. No other instance can write to it, although they can read from it for the purpose of read-consistent images.

 


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