Re: [PATCH] Negative Transition Aggregate Functions (WIP)

David Rowley <dgrowleyml@gmail.com> writes:
> I guess the answer for the people that complain about slowness could be
> that they create their own aggregate function which implements float4pl as
> the trans function and float4mi as the negative trans function. They can
> call it SUMFASTBUTWRONG() if they like. Perhaps it would be worth a note in
> the documents for this patch?

I think it would be an absolutely perfect documentation example to show
how to set up such an aggregate (and then point out the risks, of course).

> As for numeric, I did start working on this just after I posted the
> original patch and before I saw your comment about it. I did end up making
> do_numeric_desperse() which was to be the reverse of do_numeric_accum(),
> but I got stuck on the equivalent of when do_numeric_accum()
> does mul_var(&X, &X, &X2, X.dscale * 2);

Ummm ... why doesn't it work to just use numeric_add and numeric_sub,
exactly parallel to the float case?
        regards, tom lane