Re: Theoretical Basis for SELECT FOR UPDATE

vc wrote:
> Tony Andrews wrote:
> > 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.
>
> A simplistic "save just before" clearly is not enough, in the first
> place because during the time taken to read and store the 'before'
> value, the value may get too old due to the fact that another
> concurrent transaction may have just produced a newer version. A
> solution is to make the transaction that creates a new row version
> responsible for maintaining the version store.

A simplistic "lock rows" and "save just before" then.

> >I imagine DB2 et al already have something like that?
>
> It does not.

Really? How do they performs sorts then? (I realise you mean, "does not have multi-versioning", but that was NOT what I suggested they had, was it?

Anyway, this is all rather moot because the TTM's model for multiple assignment is not intended to be implemented in DB2 or any other SQL DBMS... Received on Thu Oct 06 2005 - 13:50:24 CEST