Manage
Undo Data
Before You Begin
This 5-minute tutorial shows you how to manage undo data.
Select the Oracle Database release:
Background
Oracle Database uses undo data to roll back transactions, to provide read consistency, as part of database recovery, and to enable features such as Oracle Flashback Query. Oracle Database automatically ensures that undo data that is in use by an active transaction is never overwritten until that transaction has been committed. The database server maintains and automatically tunes an undo retention period to ensure the success of Oracle Flashback features and for read consistency for long-running queries. Auto-tuning of the undo retention period is enabled when you create your database.
What Do You Need?
- Oracle Database 18c19c
View
Undo Information
To view undo data information, perform the following steps:
- Select Undo Management
in the Storage menu.
Description of the illustration a1 - The Undo Management Details page is displayed. The "Low Undo
Retention Threshold" setting shows the minimum undo retention
as configured in the UNDO_RETENTION initialization parameter.
A "Retention Guaranteed" setting of Yes indicates that the
database server should not overwrite unexpired undo data even
if current DML transactions must fail to accommodate this
setting. A setting of Yes may be necessary to support Oracle
Flashback Query. If you receive "Snapshot Too Old Errors" you
may need to increase the value of UNDO_RETENTION or increase
the size of the undo tablespace.
Description of the illustration a2 - Scroll to the right to the view the Undo Advisor graph. The
graph shows the minimum size requirement for the undo
tablespace given a particular undo retention time. You can
change the undo tablespace to a fixed size if necessary.
Changing to a fixed size may be required to support Oracle
Flashback operations.
Description of the illustration a3 - Click Change Analysis
Parameters to change the values used in the undo
configuration analysis and by the Undo Advisor.
Description of the illustration a4 - Select Last Week in
the Analysis Period menu and click OK.
Description of the illustration a5 - Click OK on the
Confirmation page .
Description of the illustration a6 - The Undo Statistics Summary and Undo Advisor sections
reflect the analysis for the last week.
Description of the illustration a7 - Click ORCL to return to the Database Home page.