UNDO_
MANAGEMENT is not a dynamic parameter; therefore, the instance must be restarted whenever
UNDO_MANAGEMENT is changed from AUTO to MANUAL, or vice versa.
UNDO_TABLESPACE
The UNDO_TABLESPACE parameter specifies which undo tablespace will be used for Automatic
Undo Management. If UNDO_MANAGEMENT is not specified or set to MANUAL, and UNDO_
TABLESPACE is specified, the instance will not start.
NOTE
UNDO_TABLESPACE is used in a Real Application Clusters (RAC)
environment to assign a particular undo tablespace to an instance,
where the total number of undo tablespaces in the database is the
same or more than the number of instances in the cluster.
View Description
DBA_TABLESPACES Tablespace names and characteristics, including the CONTENTS
column, which can be PERMANENT, TEMPORARY, or UNDO;
the undo RETENTION column is NOT APPLY, GUARANTEE, or
NOGUARANTEE.
DBA_UNDO_EXTENTS All undo segments in the database, including their size, their
extents, the tablespace where they reside, and current status
(EXPIRED or UNEXPIRED).
V$UNDOSTAT The amount of undo usage for the database at ten-minute
intervals; contains at most 1008 rows (7 days).
V$ROLLSTAT Rollback segment statistics, including size and status.
V$TRANSACTION Contains one row for each active transaction for the instance.
TABLE 7-1 Undo Tablespace Views
Chapter 7: Managing Transactions with Undo Tablespaces 217
Conversely, if UNDO_MANAGEMENT is set to AUTO and there is no undo tablespace in the
database, the instance will start, but then the SYSTEM rollback segment will be used for all undo
operations, and a message is written to the alert log.
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