Re: HOT patch, missing things

On Thu, Aug 09, 2007 at 01:25:14PM +0100, Gregory Stark wrote:
> "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com> writes:
>
> > HOT update is feasible iff
> >
> > - old and new tuples, both match the partiality condition OR
> > - old and new tuples, both don't match the condition
> ...
> > For functional index, we should apply the function to the old and new
> > tuple and compare the outcome. If the results are same, HOT update
> > is feasible.
>
> This is debatable. We could compare the columns used in the partial condition
> expression or function expression directly. If they're the same then the
> expression or function must return the same value. If the function is quite
> expensive then that might be cheaper.
>
> On the other hand if it's not expensive and the columns change frequently but
> the results don't then we might be doing a lot of work for nothing.

If we're going to get this into 8.3 I think we should be leaning towards
whatever is the simplest way to do it...
--
Decibel!, aka Jim Nasby decibel(at)decibel(dot)org
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)