Re: A qsort template

On Sun, Jul 4, 2021 at 9:58 AM Thomas Munro <thomas.munro@gmail.com> wrote:
>
> On Fri, Jul 2, 2021 at 2:32 PM John Naylor <john.naylor@enterprisedb.com> wrote:
> > I suspect if we experiment on two extremes of type "heaviness" (accessing and comparing trivial or not), such as
uint32and tuplesort, we'll have a pretty good idea what the parameters should be, if anything different. I'll do some
testingalong those lines. 
>
> Cool.
>
> Since you are experimenting with tuplesort and likely thinking similar
> thoughts, here's a patch I've been using to explore that area.  I've
> seen it get, for example, ~1.18x speedup for simple index builds in
> favourable winds (YMMV, early hacking results only).  Currently, it
> kicks in when the leading column is of type int4, int8, timestamp,
> timestamptz, date or text + friends (when abbreviatable, currently
> that means "C" and ICU collations only), while increasing the
> executable by only 8.5kB (Clang, amd64, -O2, no debug).
>
> These types are handled with just three specialisations.  Their custom
> "fast" comparators all boiled down to comparisons of datum bits,
> varying only in signedness and width, so I tried throwing them away
> and using 3 new common routines.  Then I extended
> tuplesort_sort_memtuples()'s pre-existing specialisation dispatch to
> recognise qualifying users of those and select 3 corresponding sort
> specialisations.
>
> It might turn out to be worth burning some more executable size on
> extra variants (for example, see XXX notes in the code comments for
> opportunities; one could also go nuts trying smaller things like
> special cases for not-null, nulls first, reverse sort, ... to kill all
> those branches), or not.

The patch does not apply on Head anymore, could you rebase and post a
patch. I'm changing the status to "Waiting for Author".

Regards,
Vignesh