Differences between automatic undo management and Manual undo management

Traditionally until Oracle 8i you have been using Manaul undo management which deals with roll back segments. Typically undo information is stored in rollback segments until a rollback or commit statement is issued.But now with Oracle 9i all your troubles are gone with Manual undo management. Oracle has introduced auto undo management.

Terminology differences :

In automatic undo management we call undo segment rather than rollback segment.

Automatic undo Management can be abbrevated as AUM oR sYSTEM MANAGED UNDO (SMU).

Manual undo management is usually abbrevated as MUM OR ROLLBACK UNOD (RBU).

COMPATIBILITY differences :

Automatic undo management is possible and compatible in Oracle versions 9.0.0 and higher.

Automatic Undo Management is enable by default if the database is created using database configuration assistant.

Manual undo management is not obseleted. it is even supported in the latest versions of Oracle. If you are flexible with Manual undo management ,you can even use it in Oracle version 9.x or 8.x.

You can even upgrade from Manaul undo management to Automatic undo Management.

Differences in Management of Segments :

Automatic Undo Management Mode:

Oracle will automatically name, create and manage the Undo Segments.

Oracle can control the sizing and the number of undo segments

You require an Undo tablespace for automatic undo management.

Manual Undo Management Mode:

Same as using Rollback Segments in Oracle8i and below

DBA has to create and manage the roll back segments.