Re: [HACKERS] Block level parallel vacuum

On Thu, Oct 31, 2019 at 11:33 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Tue, Oct 29, 2019 at 1:59 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > Actually after increased shared_buffer I got expected results:
> >
> > * Test1 (after increased shared_buffers)
> > normal : 2807 ms (hit 56295, miss 2, dirty 3, total 56300)
> > 2 workers : 2840 ms (hit 56295, miss 2, dirty 3, total 56300)
> > 1 worker : 2841 ms (hit 56295, miss 2, dirty 3, total 56300)
> >
> > I updated the patch that computes the total cost delay shared by
> > Dilip[1] so that it collects the number of buffer hits and so on, and
> > have attached it. It can be applied on top of my latest patch set[1].

While reading your modified patch (PoC-delay-stats.patch), I have
noticed that in my patch I used below formulae to compute the total
delay
total delay = delay in heap scan + (total delay of index scan
/nworkers). But, in your patch, I can see that it is just total sum of
all delay. IMHO, the total sleep time during the index vacuum phase
must be divided by the number of workers, because even if at some
point, all the workers go for sleep (e.g. 10 msec) then the delay in
I/O will be only for 10msec not 30 msec. I think the same is
discussed upthread[1]

[1] https://www.postgresql.org/message-id/CAA4eK1%2BPeiFLdTuwrE6CvbNdx80E-O%3DZxCuWB2maREKFD-RaCA%40mail.gmail.com

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