Re: changing rollback segment initial extent

In article <39afd7d5$1_at_news.iprimus.com.au>,   "Howard J. Rogers" <howardjr_at_iprimus.com> wrote:
>
> "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
>

Actually setting the minextents to 20 is Oracle current recommendation and is available in a white paper available from support. I do not have the number but I have seen Oracle support post links to it in Metalink within the last six months. You might be able to find it at www.orapub.com also.

--
Mark D. Powell  -- The only advice that counts is the advice that
 you follow so follow your own advice --


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