From: Ron <ronljohnsonjr@gmail.com>
To: pgsql-admin@lists.postgresql.org
Subject: Re: IO scheduler recommendation
Date: Tue, 22 Jan 2019 01:12:20 -0600
Message-ID: <612605b8-c94b-68a3-3e8f-0134ddcfe71d@gmail.com> (raw)
In-Reply-To: <CAC=50j-j3e7NX2mPGLYfsoPTVVq=Nrp4TPesLKDrNxQK+snUDg@mail.gmail.com>
References: <CAHMim6rF6jxUp1ueJP593SwM4so7jsZC0vZaXOX2yD_z4XF9xQ@mail.gmail.com>
<df772cb764b99d4f4a454ee307840022c91bcdb6.camel@cybertec.at>
<CAHMim6qzmodYXJtnOQBU-ge5Q0WHKsPOkFkLMSBLB5YShae0oQ@mail.gmail.com>
<CAC=50j-j3e7NX2mPGLYfsoPTVVq=Nrp4TPesLKDrNxQK+snUDg@mail.gmail.com>
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@gmail.com
> <mailto:bharti.anup@gmail.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.albe@cybertec.at
> <mailto:laurenz.albe@cybertec.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
>
--
Angular momentum makes the world go 'round.
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To: pgsql-admin@postgresql.org
Cc: ronljohnsonjr@gmail.com, pgsql-admin@lists.postgresql.org
Subject: Re: IO scheduler recommendation
In-Reply-To: <612605b8-c94b-68a3-3e8f-0134ddcfe71d@gmail.com>
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