Types of Undo Data
There are three types of undo segments. The first two are similar to the two types of tablespaces—SYSTEM and non-SYSTEM—and the third is called deferred.
SYSTEM
SYSTEM undo segments are used for objects in the SYSTEM tablespace. The SYSTEM undo segment is created in the SYSTEM tablespace whenever a database is created and works the same regardless of whether the maintenance mode is manual or automatic.
Non-SYSTEM
Non-SYSTEM undo segments are used for all objects in any tablespace other than the SYSTEM tablespace. These segments can either be created with automatic undo management or manual undo management. The two different ways that segments can be managed are detailed as follows:
Manual undo management In manual undo management ...
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