Re: IO scheduler recommendation

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> 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>
> 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