UNDO MANAGEMENT

Migrating to Automatic Undo Management

Although Oracle strongly recommends to use UNDO Management instead of Manual rollback segments, at my previousorgaization, we were shifted from auto undo management to manual rollback segments.I had discussed the reason behind this shift in my old article titled as 'Auto Undo Management performance degradation'.

The problem was with Oracle 9i (9205) version. Now I heard that the database already upgraded to 10gR2.

I am really inspired by the following features of 10gR2 about Auto Undo Management. Therefore,I will recommend my ex-boss to revert back to UNDO MANAGEMENT option.

I can convieance him with the following valid reasons:

Reason One: - Fast Ramp-Up in 10gR2.

In Oracle10gR2 , when the database startsup, undo segments which status were online during the shutdown will be online again. This will avoid the overhead of bringing undo segments online on a heavy OLTP database.

Reason Two: - Migration easy step.

To get an idea how long the UNDO talespace should be, can be easily done by using DBMS_UNDO_ADV.RBU_MIGRATION package provided in 10gr2.

DECLARE
utbsiz_in_MB NUMBER;
BEGIN utbsiz_in_MB := DBMS_UNDO_ADV.RBU_MIGRATION;
end;/


http://www.oracle.com/technology/oramag/oracle/05-jul/o45tuning.htmlhttp://download-uk.oracle.com/docs/cd/B19306_01/server.102/b14231/undo.htm

Reason Three:
Undo guarantee and Automatic Tuning of Undo Retention.


Happy Reading,
poorna