Re: Theoretical Basis for SELECT FOR UPDATE

vc wrote:
> Tony Andrews wrote:
> > vc wrote:
> [...]
> > > This feature is interesting because in fact it implies that the
> > > hypothetical database has to implement multiversioning. How else can
> > > it get the last consistent value of 'a' after 'a' has already been
> > > changed ? This would exclude from consideration all purely locking
> > > databases similar to DB2, SQL Server, Informix, Sybase, etc.
> >
> > Well I suppose the DBMS could gather all the data it will need before
> > it changes any and store it temporarily somewhere?
>
> That's what multiversioning does, more or less ;)

More or less maybe, but you DON'T need the full works of multi-versioning just to store data temporarily; you just need a TEMP data area or enough memory. I imagine DB2 et al already have something like that? Received on Wed Oct 05 2005 - 18:42:34 CEST