RE: A rollback segment question on minextents

Actually the rollback segment header in the first extent exists in a single block, the rest of the first extent, as I understand it, is available for undo. Thus making INITIAL and NEXT the same should be of no consequence in this regard.

It is my understanding (and I'm sure I will be corrected if I'm wrong) the reason for a requirement of 2 extents is to allow the tail/wrap architecture that Oracle uses for rollback segments.

RF

Robert G. Freeman - Oracle8i OCP
Oracle DBA Technical Lead
CSX Midtier Database Administration

The Cigarette Smoking Man: Anyone who can appease a man's conscience can take his freedom away from him.

-----Original Message-----
Sent: Friday, March 15, 2002 12:54 PM
To: Multiple recipients of list ORACLE-L

Oracle recommends the size NEXT=INITIAL. So if I had 10M initial, then most of the initial beyond the header info will be wasted? Sure not!

Kumanan

> -----Original Message-----
> From: Rachel Carmichael [SMTP:wisernet100_at_yahoo.com]
> Sent: 11 March 2002 21:48
> To: Multiple recipients of list ORACLE-L
> Subject: RE: A rollback segment question on minextents
>
> the first extent is used by oracle as the segment header to manage the
> transaction information within the rollback segment. The second extent
> contains the actual change vectors
>
>
> --- kumanan.balasundaram_at_qxl.com wrote:
> > Hi,
> >
> > My point was that it could allocate one more extent as per need. Why
> > the
> > need to minextents = 2?
> >
> > Thanks
> > Kumanan
> >
> > > -----Original Message-----
> > > From: Stephane Faroult [SMTP:sfaroult_at_oriole.com]
> > > Sent: 07 March 2002 20:54
> > > To: Multiple recipients of list ORACLE-L
> > > Subject: Re: A rollback segment question on minextents
> > >
> > > kumanan.balasundaram_at_qxl.com wrote:
> > > >
> > > > Hi,
> > > >
> > > > I was wondering why Oracle force minextents for rollback
> > > > segments to be two. Why can't we have minextents zero or
> > > > no minextents clause at all.
> > > >
> > > > We can surely set initial extent to be large enough ourselves
> > > > and next extent sized accordingly.
> > > >
> > > > Can someone enlighten me on the reason/thought behind this?
> > > >
> > > > Many thanks
> > > >
> > > > Kumanan Balasundaram
> > > > Database Administrator, IT
> > > > QXL ricardo plc
> > > > www.qxl.com
> > > > P: +44 (0)208 962 7409
> > >
> > > Oracle doesn't reuse an extent which contains active transactions.
> > What
> > > do you think would happen when you reach the end of your initial
> > extent
> > > ? Exactly.
> > > --
> > > Regards,
> > >
> > > Stephane Faroult
> > > Oriole Ltd
> > > --
> > > Please see the official ORACLE-L FAQ: http://www.orafaq.com
> > > --
> > > Author: Stephane Faroult
> > > INET: sfaroult_at_oriole.com
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> Author: Rachel Carmichael
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-- 
Author: 
  INET: kumanan.balasundaram_at_qxl.com

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Author: Freeman, Robert 
  INET: Robert_Freeman_at_csx.com

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