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. 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. All rights reserved by Burleson. This script will monitor UNDO usage changes: select substr a. Click here for instructions on how to enable JavaScript in your browser. Oracle DBA. Tablespace management. Monitor who is using UNDO: select s. Cancel reply Save my name, email, and website in this browser for the next time I comment.
You can specify an undo pool for each consumer group. An undo pool controls the amount of total undo that can be generated by a consumer group. When the total undo generated by a consumer group exceeds its undo limit, the current UPDATE transaction generating the redo is terminated. No other members of the consumer group can perform further updates until undo space is freed from the pool.
This section lists views that are useful for viewing information about undo space in the automatic undo management mode and provides some examples. In addition to views listed here, you can obtain information from the views available for viewing tablespace and datafile information. Please refer to " Viewing Datafile Information" for information on getting information about those views.
Oracle Database also provides proactive help in managing tablespace disk space use by alerting you when tablespaces run low on available space.
Please refer to "Managing Space in Tablespaces " for information on how to set alert thresholds for the undo tablespace. To prevent excessive alerts, the long query alert is issued at most once every 24 hours. When the alert is generated, you can check the Undo Advisor Page of Enterprise Manager to get more information about the undo tablespace. The following dynamic performance views are useful for obtaining space information about the undo tablespace:. Statistics are available for undo space consumption, transaction concurrency, the tuning of undo retention, and the length and SQL ID of long-running queries in the instance.
Each row in the view contains statistics collected in the instance for a ten-minute interval. Each column represents the data collected for the particular statistic in that time interval. The first row of the view contains statistics for the partial current time period. The view contains a total of rows, spanning a 7 day cycle. Your Oracle Database includes several features that are based upon undo information and that allow administrators and users to access database information from a previous point in time.
These features are part of the overall flashback strategy incorporated into the database and include:. The retention period for undo information is an important factor for the successful execution of Flashback features. It determines how far back in time a database version can be established. Specifically, you must choose an undo retention interval that is long enough to enable users to construct a snapshot of the database for the oldest version of the database that they are interested in.
Using Oracle Flashback Query feature, users or applications can execute queries as of a previous time in the database. Application developers can use Flashback Query to design an application that allows users to correct their mistakes with minimal DBA intervention.
You, as the DBA, need only configure the undo tablespace with an appropriate size and undo retention period. No further action on your part should be required. The Flashback Version Query feature enables users to query the history of a given row. Otherwise, not all rows can be retrieved. One use for this view could be if a user finds, by using the Flashback Transaction Query feature, that a row value has been changed inappropriately.
It provides a fast, online solution for recovering a table that has been accidentally modified or deleted by a user or application.
If you are still using rollback segments to manage undo space, Oracle strongly recommends that you migrate your database to automatic undo management. Oracle Database provides a function that provides information on how to size your new undo tablespace based on the configuration and usage of the rollback segments in your system. DBA privileges are required to execute this function:. Set the warning and critical alert thresholds for the undo tablespace alert properly.
It contains the following topics: What Is Undo? What Is Undo? See Also: "Migration to Automatic Undo Management" for information on how to migrate to automatic undo management. Introduction to Automatic Undo Management This section introduces the concepts of Automatic Undo Management and discusses the following topics: Overview of Automatic Undo Management Undo Retention Retention Guarantee Overview of Automatic Undo Management In past releases, when you used the rollback segment method of managing undo space, you were said to be operating in the manual undo management mode.
Notes: You cannot use both methods in the same database instance, although for migration purposes it is possible, for example, to create undo tablespaces in a database that is using rollback segments, or to drop rollback segments in a database that is using undo tablespaces. This parameter should be used only when the database has multiple undo tablespaces and you want to direct the database instance to use a particular undo tablespace.
The default is seconds. The setting of this parameter should take into account any flashback requirements of the system. See Also: Oracle Database Reference for complete descriptions of initialization parameters used in automatic undo management mode. Undo Retention Committed undo information normally is lost when its undo space is overwritten by a newer transaction.
Automatic Tuning of Undo Retention Oracle Database 10 g automatically tunes undo retention by collecting database use statistics and estimating undo capacity needs for the successful completion of the queries. Retention Guarantee Oracle Database 10 g lets you guarantee undo retention.
Sizing the Undo Tablespace You can size the undo tablespace appropriately either by using automatic extension of the undo tablespace or by manually estimating the space you will need for undo. Using Auto-Extensible Tablespaces Oracle Database supports automatic extension of the undo tablespace to facilitate capacity planning of the undo tablespace in the production environment.
Sizing Fixed-Size Undo Tablespaces If you have decided on a fixed-size undo tablespace, the Undo Advisor can help you estimate needed capacity, and you can then calculate the amount of retention your system will need. However, since most aspects of undo tablespaces are system managed, you need only be concerned with the following actions: Adding a datafile Renaming a datafile Bringing a datafile online or taking it offline Beginning or ending an open backup on a datafile Enabling and disabling undo retention guarantee These are also the only attributes you are permitted to alter.
Switching Undo Tablespaces You can switch from using one undo tablespace to another. If any of the following conditions exist for the tablespace being switched to, an error is reported and no switching occurs: The tablespace does not exist The tablespace is not an undo tablespace The tablespace is already being used by another instance in a RAC environment only The database is online while the switch operation is performed, and user transactions can be executed while this command is being executed.
0コメント