Re: Parallel Seq Scan vs kernel read ahead

Em qua., 20 de mai. de 2020 às 21:03, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
escreveu:

> On Thu, May 21, 2020 at 11:51 AM Ranier Vilela <ranier(dot)vf(at)gmail(dot)com>
> wrote:
> > Em qua., 20 de mai. de 2020 às 20:48, Thomas Munro <
> thomas(dot)munro(at)gmail(dot)com> escreveu:
> >> On Thu, May 21, 2020 at 11:15 AM Ranier Vilela <ranier(dot)vf(at)gmail(dot)com>
> wrote:
> >> > postgres=# set max_parallel_workers_per_gather = 0;
> >> > Time: 227238,445 ms (03:47,238)
> >> > postgres=# set max_parallel_workers_per_gather = 1;
> >> > Time: 138027,351 ms (02:18,027)
> >>
> >> Ok, so it looks like NT/NTFS isn't suffering from this problem.
> >> Thanks for testing!
> >
> > Maybe it wasn’t clear, the tests were done with your patch applied.
>
> Oh! And how do the times look without it?
>
Vanila Postgres (latest)

create table t as select generate_series(1, 800000000)::int i;
set max_parallel_workers_per_gather = 0;
Time: 210524,317 ms (03:30,524)
set max_parallel_workers_per_gather = 1;
Time: 146982,737 ms (02:26,983)

regards,
Ranier Vilela