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FAQ – Automatic Undo Management (AUM) / System Managed Undo (SMU) (Doc ID 461480.1)

Last updated on MARCH 06, 2025

Applies to:

Oracle Database - Enterprise Edition - Version 9.2 and later
Information in this document applies to any platform.
Oracle RDBMS Server



Purpose

This article is intended for Database Administrators with  knowledge on Automatic Undo Management (AUM).

Also covered major questions related to Automatic Undo Management (AUM) which will be helpful during creation (or) monitoring the undo tablespaces.

Questions and Answers

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In this Document
Purpose
Questions and Answers
 What is Undo?
 Which are the major initialization parameters that controls AUM?

 How to set the undo_retention value ?
 What is the Fast Ramp-up Routine ?
 
How to switch to a new undo tablespace?
 What is UNDO Retention?
 What is Automatic UNDO Retention (10g New Feature)? Explain.
  Why TUNED_UNDORETENTION is calculated so high making undo space grow fast ?
 Explain the DBA_UNDO_EXTENTS View, and usage?
 What are the various statuses for Undo Extents? Explain.
 
Explain V$TRANSACTION, and usage?
 Explain DBA_ROLLBACK_SEGS, and usage?
 Do we have scripts to monitor the undo growth/usage of the database?
 
What are the possible causes for excessive undo growth?
 How to resize the undo datafile?
 Drop Undo Tablespace
 What is In Memory Undo?
References

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