Re: Rollback segments

The point, I think, is one you have missed. In Oracle 8i, transactions can share BLOCKS, provided one of them is committed or rolled back (ie, dead).

Transactions have been able to share extents since Oracle 7.1 ... this much is NOT news.

Regards
HJR "Naushi Hussain" <naushi.hussain_at_alliedsignal.com> wrote in message news:3A64898F.2A89A427_at_alliedsignal.com...
> just like to mention here that more than one transactions can stay in one
 extent
> if there is room but a block can contain only one transaction at a time.
>
> "Howard J. Rogers" wrote:
>
> > "Greg Stark" <greg-spare-1_at_mit.edu> wrote in message
> > news:87k882xiea.fsf_at_stark.yi.org...
> > > "Howard J. Rogers" <howardjr_at_www.com> writes:
> > >
> > > > Incidentally, you are asking for trouble having rollback segments
 with
 only
> > > > two extents. The chances of them having to acquire more extents is
 very
> > > > high (assuming you eventually bring them online).
> > > >
> > > > Rollbacks should have around half a dozen extents to minimise the
 need
 to
> > > > extend dynamically
> > >
> > > I don't understand how you can say that without knowing the size of
 the
> > > extents and activity. Is there any major functional difference between
 a
> > > rollback segment with 6 1M extents and a rollback segment with 2 3M
 extents?
> > >
> > >
> > > --
> > > greg
> >
> > Yes, a huge one. New transactions cannot move into an extent of a
 rollback
> > segment which has an active transaction within it. With just two
 extents,
> > the chances of filling up the second extent and thereby needing to move
 back
> > into the first which is likely to still have one active transaction in
 it
> > (however trivial that transaction is) is extremely high. The more
 extents
> > you have, the lower the probability. When it can't move back into the
 first
> > extent because of the presence of an active transaction, the segment
 will
> > instead acquire (dynamically) an additional extent.
> >
> > Since it is the presence of a single transaction that prevents extent
 reuse,
> > it's the number of extents, not the size of them per se that is the
 trouble.
> > 2 3M extents are, other things being equal, much more likely to have a
> > single live transaction in them somewhere than 6 1M extents. Of course,
 it
> > should take longer to fill up the second extent, and thus need (or,
 rather,
> > want) to move back into the first... but we are talking probabilities
 here.
> > You are more *likely* to need to acquire a third extent. Naturaly,
 activity
> > levels determine the actual need, or lack thereof, for doing so.
> >
> > Regards
> > HJR
>
Received on Wed Jan 17 2001 - 04:59:58 CST