Re: IO scheduler recommendation

Isn't the use of NFS pretty high on the "things not to do with Postgres" list?

On 1/22/19 12:13 AM, Tim Cross wrote:
> I suspect the main reason there are no official recommendations is because
> setting the IO scheduler is a  low level optimisation, getting very close
> to a 'mciro-optimisation' compared to other areas of optimisation.  Some
> even consider playing at this level to be somewhat of a black art -
> primarily because it is very complicated and dependent on many, many
> variables (hardware, use profile, data profile etc). For these reasons, I
> doubt there is a clear 'winner' for PG (especially as PG doesn't do direct
> IO to disk like Oracle does).  I suspect the fact your using NFS will
> overshadow any differences with the IO scheduling algorithm as well. 
> Regardless, the only reliable way to select the best algorithm would be
> extensive benchmarking using realistic data and usage profiles.
>
> On Tue, 22 Jan 2019 at 16:38, AB_ba# <bharti(dot)anup(at)gmail(dot)com
> <mailto:bharti(dot)anup(at)gmail(dot)com>> wrote:
>
> Thanks Laurenz
> Surprise to know that there are no official recommendation from
> PostgreSQL.
>
> On Mon, Jan 21, 2019 at 9:14 PM Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at
> <mailto:laurenz(dot)albe(at)cybertec(dot)at>> wrote:
>
> AB_ba# wrote:
> > I searched the complete PostgreSQL Documentation but didn't get
> anything with respect to IO scheduler recommendation.
> > What is being recommended by PostgreSQL ?
>
> There is no clear recommendation.
>
> I personally have seen workloads where changing from "cfq" to
> "deadline"
> or "noop" improved performance by a factor of 4, but on many
> systems "cfq"
> seems to be doing at least as good as the others.
>
> I believe that it depends a lot on your hardware configuration and
> your workload, and you are best advised to run a realistic load test.
>
> > Which is the best IO scheduler considering the Data is hosted on
> NFS?
>
> No idea - probably depends on what is behind the NFS.
>
> Make sure to use hard, fg mounts.
> If you can, use "jumbo frames" so that an 8KB block can fit into
> a single IP frame.
>
> Yours,
> Laurenz Albe
> --
> Cybertec | https://www.cybertec-postgresql.com
>
>
>
> --
> Thanks and Regards
> ANUP BHARTI
>
>
>
> --
> regards,
>
> Tim
>
> --
> Tim Cross
>

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