Re: What's in a Rollback Segment?

Hi Howard,

No worries :)

Do you know where this behaviour might be formally documented. I have notes in my notes but most unlike me I don't have a reference to them listed.

Thanks

Richard
"Howard J. Rogers" <howardjr2000_at_yahoo.com.au> wrote in message news:ahb8qu$qhq$1_at_lust.ihug.co.nz...
>
> "Richard Foote" <richard.foote_at_bigpond.com> wrote in message
> news:fy8_8.39133$Hj3.118612_at_newsfeeds.bigpond.com...
> > Hi Howard,
> >
> > Just the row being updated and "overhead" to identify the undo data.
> >
> > I read somewhere (although I've never bothered to check this) that a
> > rollback block *can* be shared by other transactions. They can't be
shared
> > concurrently but can be used after the first transaction has complete
(and
> I
> > don't mean clobbering the first transactions undo, I mean using the
unused
> > bit and having both transactions (or more) redo available).
> >
> > Myth or legend, I'm not sure.
>
>
> That's true from 8.1.6 onwards, I think. Jonathan put me onto that about
12
> months ago (the posts will be on Google somewhere).
>
> Didn't want to get complicated at this stage, but just answer the question
> as posed about 'whole block-whole row or just-column'.
>
> Regards
> HJR
>
> >
> > Regards
> >
> > Richard
> > "Howard J. Rogers" <howardjr2000_at_yahoo.com.au> wrote in message
> > news:ahb40d$e8f$1_at_lust.ihug.co.nz...
> > > It's just the column of the row being updated. Your few-byte
transaction
> > is
> > > thus going to occupy an entire 8192 bytes of a rollback segment (ie, a
> > > transaction always occupies an entire rollback block, however small it
> is
> > in
> > > itself).
> > >
> > > Regards
> > > HJR
> > >
> > >
> > > "Jeremy Russell" <jeremy.russell-NOTMYREALADDRESS_at_usa.net> wrote in
> > message
> > > news:3d39010b.50393862_at_usenet.plus.net...
> > > > OK, maybe it's too early in the morning, and maybe I'm just dumb,
but
> > > > what - in detail - is written to a rollback segment in Oracle 8i? I
> > > > understand that a rollback segment records undo info for a
transaction
> > > > (used Oracle long enough for that level of comprehension at least!),
> > > > but it was my understanding that the entire block would be written
out
> > > > for potential read consistency, recovery, rollback purposes.
> > > >
> > > > However, I have a feeling that may not be true.
> > > >
> > > > If I issue
> > > >
> > > > UPDATE emp SET ename='RUSSELL' where empno=7369;
> > > >
> > > > does the entire block where this employee resides get written, is it
> > > > the entire row or is it just the changed column?
> > > >
> > > > If there's a link somewhere (technet or otherwise) that explains
this,
> > > > please let me have that, rather than taking up newsgroup bandwidth.
> > > >
> > > > TIA
> > > >
> > > > Jeremy Russell
> > >
> > >
> >
> >
>
>
Received on Sat Jul 20 2002 - 08:17:27 CDT