Re: IO scheduler recommendation

"AB_ba#" <bharti.anup@xxxxxxxxx> · Tue, 22 Jan 2019 14:10:33 +0530

It all depends on your experience, There are number of deployments that are working great with NFS.

Also,IO scheduler settings applies to block devices not to NFS.

On Tue, Jan 22, 2019 at 12:42 PM Ron <ronljohnsonjr@xxxxxxxxx> wrote:

    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.anup@xxxxxxxxx>
          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.albe@xxxxxxxxxxx>
              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

    -- 

      Angular momentum makes the world go 'round.

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Thanks and Regards
ANUP BHARTI