Re: MVCC, undo log, and HOT

On Mon, 2007-10-22 at 11:00 -0400, Bruce Momjian wrote:
> Joshua D. Drake wrote:
> > Josh Berkus wrote:
> > > Bruce Momjian wrote:
> > >> Those who have been with the community from long ago might remember
> > >> discussion about implementing a undo log.  The big advantage of this is
> > >> that it allows UPDATE to _replace_ rows and limits the amount of cleanup
> > >> required for UPDATEs.
> > >>
> > >> I am hoping that with HOT we will no longer have any need to even
> > >> consider undo.
> > >>
> > > 
> > > We were considering it?
> > 
> > I don't ever remember us considering it seriously.
> > 
> > > 
> > > I certainly wasn't.  I've enough experience with Oracle and InnoDB to 
> > > see that an undo log is its own set of performane issues.   No thanks.
> > > 
> > 
> > It certainly does.
> 
> We never actually considred undo

I did, but eventually ruled it out during the HOT design process. But
then I considered a ton of other things and ruled them out also.

Can't see a reason to bring it up again, so perhaps we should add it to
the definitely don't want list. Don't *need* would be better.

--  Simon Riggs 2ndQuadrant  http://www.2ndQuadrant.com