Re: WITHIN GROUP patch

>>>>> "Tom" == Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

Tom> I've committed this after significant editorialization --- most
Tom> notably, I pushed control of the sort step into the aggregate
Tom> support functions.

Initial tests suggest that your version is ~40% slower than ours on
some workloads.

On my system, this query takes ~950ms using our dev branch of the code,
and ~1050ms on git master (using \timing in psql for timings, and taking
the best of many consecutive runs):

select count(*)
from (select percentile_disc(0.5) within group (order by i)
from generate_series(1,3) i, generate_series(1,100000) j group by j) s;

About ~700ms of that is overhead, as tested by running this query with
enable_hashagg=false:

select count(*)
from (select j
from generate_series(1,3) i, generate_series(1,100000) j group by j) s;

So your version is taking 350ms for the percentile calculations
compared to 250ms for ours.

--
Andrew (irc:RhodiumToad)