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abukta
super admin
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Join Date: 29 Mar 2005 21:03
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Monitoring Rollback Segment |
Rollback segmenst are used to keep track of exactly how data looked before it was modified. Why is this important? Rollback segment esures that you won't see mixed modified and unmodified data so you can always see a consistent picture of the data, even if someone is making changes to it.
Defining the right size for the rollback segment is a very important DBA task because it has direct impact on performance.
To look at the optimal value, shrinks and extends, you can use the following script:
column Name format A20
select Name, OptSize, Shrinks, AveShrink, Extends
from V$ROLLSTAT, V$ROLLNAME
where V$ROLLSTAT.USN = V$ROLLNAME.USN
/
* USN - (U)ndo (S)egment (N)umber
If your rollback segment is sized correctly, you will see low or "0" values for the number of extends and shrinks. This makes sure that Oracle does not preform a great deal of unnecessary space management work.
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