Re: Gather performance analysis

On Tue, Sep 28, 2021 at 5:21 PM Tomas Vondra
<tomas.vondra@enterprisedb.com> wrote:
> >> Yeah, if it is losing in some cases then it is definitely good to know
> >> the reason, I was just looking into the performance numbers shared by
> >> Tomas in query-results, I can see the worst case is
> >> with 10000000 rows, 10 columns and 4 threads and queue size 64k.
> >> Basically, if we see the execution time with head is ~804ms whereas
> >> with patch it is ~1277 ms.  But then I just tried to notice the
> >> pattern with different queue size so number are like below,
> >>
> >>                            16k             64k       256k        1024k
> >> Head               1232.779    804.24    1134.723    901.257
> >> Patch              1371.493    1277.705    862.598    783.481
> >>
> >> So what I have noticed is that in most of the cases on head as well as
> >> with the patch, increasing the queue size make it faster, but with
> >> head suddenly for this particular combination of rows, column and
> >> thread the execution time is very low for 64k queue size and then
> >> again the execution time increased with 256k queue size and then
> >> follow the pattern.  So this particular dip in the execution time on
> >> the head looks a bit suspicious to me.
> >>
> >
> > I concur with your observation. Isn't it possible to repeat the same
> > test in the same environment to verify these results?
> >
>
> I can repeat any tests we need on that machine, of course.
>

I think that would be great, can we just test this specific target
where we are seeing a huge dip with the patch, e.g.
with 10000000 rows, 10 columns and 4 threads, and queue size 64k.  In
my performance machine, I tried to run this test multiple times but on
the head, it is taking ~2000 ms whereas with the patch it is ~1500 ms,
so I am not able to reproduce this.  So it would be good if you can
run only this specific test and repeat it a couple of times on your
performance machine.

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com