Re: changing rollback segment initial extent

From: Howard J. Rogers <howardjr_at_iprimus.com>
Date: Sat, 2 Sep 2000 03:23:45 +1100
Message-ID: <39afd7d5$1@news.iprimus.com.au>

"Miller Ray (Softlab)" <Ray.Miller_at_Softlab.co.uk> wrote in message news:9EC5A3A16E4BD41180730008C78432AC043155_at_birexb01.softlab.co.uk...

Problem: I need to increase the initial extent of serveral existing rollback segments. Since I cannot alter the initial extent of an existing rollback segment, I plan to do the following:

1) offline the rollback segment
2) drop the rollback segment
3) create a new rollback segment having the same name as the old

rollback segment and with new values for initial and next extents 4) online this new rollback segment
That should work. You should look to be doing the work at a quiet time. You might also want to coalesce free space after deleteing each rollback segment to minimize fragmentation.
Aim to create 20 extents in each segment initially

Please don't aim to create 20 extents. That number is a popular one that goes around the traps, based on old data from Oracle 6 databases. In Oracle 6, transactions couldn't share *extents*, and it was accordingly necessary to have lots of extents to accomodate lots of simultaneous transactions.

That hasn't been true since Oracle 7.1 (from memory), and the number of extents doesn't need to be any more than the half dozen or so which is apropriate for any form of segment.

Regards
HJR

Match the number of segments to the number of users (between 4 and 10 users to 1 segment), and make sure that the init.ora file reflects the number of segments if you want them online by default. Talk to oracle about using the optimal setting (works on some OSs and not on others apparently).
Ray Received on Fri Sep 01 2000 - 11:23:45 CDT