Re: [HACKERS] Hash support for grouping sets

On 2017-03-23 03:43:57 +0000, Andrew Gierth wrote:
> >>>>> "Andres" == Andres Freund <andres@anarazel.de> writes:
> 
>  Andres> Changes to advance_aggregates() are, in my experience, quite
>  Andres> likely to have performance effects.  This needs some
>  Andres> performance tests.
>  [...]
>  Andres> Looks like it could all be noise, but it seems worthwhile to
>  Andres> look into some.
> 
> Trying to sort out signal from noise when dealing with performance
> impacts of no more than a few percent is _extremely hard_ these days.

Indeed. But that doesn't mean we needn't try.  With some determination
and profiling you can often sepearate signal from noise - I managed to
track down 0.12% regressions in the expression evaluation work...


> I will go ahead and do this, out of sheer curiosity if nothing else,
> but the preliminary results suggest there's probably nothing worth
> holding up the patch for.

Agreed. I'd want to run one more profile, checking whether the profiles
indicate new hotspots, but other than that...

Greetings,

Andres Freund