Re: Questionable coding in orderedsetaggs.c

On Sunday, January 26, 2014, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Jeremy Harris <jgh(at)wizmail(dot)org <javascript:;>> writes:
> > In ordered_set_startup() sorts are initialised in non-randomAccess mode
> > (tuplesort_begin_heap() and ~datum(), last argument).
>
> > The use of tuplesort_skip_tuples() feels very like a random access to
> > me. I think it doesn't fail because the only use (and implementation)
> > is to skip forwards; if backwards were tried (as the interface permits)
> > external sorts would fail because multiple tapes are present for
> > FINALMERGE.
>
> Well, we certainly don't want to incur the overhead of randomAccess mode
> when we're not actually going to use it, so I'd resist changing the code
> in ordered_set_startup().
>
> It's true that if tuplesort_skip_tuples() supported backwards skip, it
> would need to insist that randomAccess mode be enabled *when a backwards
> skip is used*. But such a feature is purely hypothetical ATM.
>
>
>

+1

In ordered set functions, we normally don't skip backwards and skip tuples
while sorting in,for e.g. Hypothetical set functions in only a forward
manner.

--
Regards,

Atri
*l'apprenant*