Re: hint in determining effective_io_concurrency

On Thu, Apr 22, 2021 at 2:55 PM Luca Ferrari <fluca1978(at)gmail(dot)com> wrote:
>
> On Thu, Apr 22, 2021 at 9:52 PM Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> >
> > On Thu, Apr 22, 2021 at 09:45:15PM +0200, Luca Ferrari wrote:
> > > Hi all,
> > > I'm unable to find (apparently) a way to find out a possible value to
> > > start with for effective_io_concurrency.
> > > I suspect that benchmarking, e.g., using bonnie++ or sysbench and
> > > testing with different values of concurrency could help to determine
> > > the max number of concurrent request, (tps, lower latency, ecc.).
> > > Is thjs correct or is there another suggested way?
> >
> > I recommend 256 for SSDs or other RAM-like fsync systems, and maybe
> > maybe 16 for magnetic.
>
>
> Thanks Bruce, this is a very good starting point.
> But is there a rationale about those numbers? I mean, if I change the
> storage system, how should I set a correct number?

See thread, https://postgrespro.com/list/thread-id/2069516

The setting only impacts certain scan operations, it's not a gamechanger.

merlin