Re: What's in a Rollback Segment?

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.

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 - 02:52:41 CDT