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Home -> Community -> Usenet -> c.d.o.server -> Re: changing rollback segment initial extent
"Mark D Powell" <markp7832_at_my-deja.com> wrote in message
news:8ootgg$76d$1_at_nnrp1.deja.com...
> 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.
I know it's their recommendation, and it's still in all the training materials, too. And they even include the graph that shows you the probability of having to acquire an extra extent, and magically the graph levels out at around 20 extents. It just happens not to be true, for the reasons I explained earlier.
There is usually a bun-fight on the courses when I explain it, too!
I mean, obviously it won't kill anyone to have 20 extents. It's just entirely unnecessary.
Regards
HJR
>
> >
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