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Oracle Tips by Burleson |
OCP Instructors Guide for
Oracle DBA Certification
Chapter 5 - Oracle Database
Objects
Batch and On-line Processing
Applications that consist of batch jobs that
perform heavy DML processing (UPDATE, INSERT, DELETE) and on-line
transactions that perform minimal updates complicate the rollback
segment sizing process. The ultimate solution is to have:
-
The on-line transactions use smaller rollback
segments. Smaller rollback segments have a greater chance to be
cached in memory and are more quickly allocated than their larger
counterparts.
-
The heavy DML processing batch transactions use
the larger rollback segments. Larger rollback segment extents means
less extents required to hold before images and an increase in
performance (due to the overhead of extent allocation).
The SET TRANSACTION USE ROLLBACK SEGMENT xxxx
command can be used to control the placement of these large (or
small) transactions. The SET TRANSACTION statement allows the
developer to "point" their transaction to a particular rollback
segment.
If the bulk of the heavy DML processing is done
during off-hours, the DBA is able to "switch" rollback segments on
and off by running batch scripts that execute the ALTER ROLLBACK
SEGMENT xxxx (OFFLINE/ONLINE) command. Before the nightly batch run
begins, a script can be automatically executed to bring the large
rollback segments on-line and the small rollback segments off-line.
The last step of the nightly batch run performs the reverse. The
smaller rollback segments are brought on-line while their larger
counterparts are turned off.
The above text is
an excerpt from:
OCP Instructors Guide for Oracle DBA Certification
A Study Guide to Advanced Oracle Certified Professional Database
Administration Techniques
ISBN 0-9744355-3-8
by Christopher T. Foot
http://www.rampant-books.com/book_2003_2_OCP_print.htm
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