Thread: [Postgres-xc-developers] IO PGXC

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postgres-xc-developers

[Postgres-xc-developers] IO PGXC

From: Arni S. <Arn...@md...> - 2013-03-01 19:21:33

Users,

I have 20 nodes sitting on a disk arrays, with multiple LUNs. when I issue queries - `select count(1) from table` for example, I am experiencing heavy writes and heavy reads. I expected the reads but not the writes and it has really thrown a wrench in the caching. My first assumption would be the log files, do you have any other ideas what could be causing all these writes with a select?

Arni Sumarlidason | Software Engineer, Information Technology
MDA | 820 West Diamond Ave | Gaithersburg, MD | USA
O: 240-833-8200 D: 240-833-8318 M: 256-393-2803
arn...@md...<mailto:arn...@md...>| http://www.mdaus.com<http://www.mdaus.com/>

Re: [Postgres-xc-developers] [Postgres-xc-general] IO PGXC

From: Nikhil S. <ni...@st...> - 2013-03-01 19:33:48

Hi Arni,

Am guessing that hint bits could be causing the I/O. See here:

http://wiki.postgresql.org/wiki/Hint_Bits

Regards,
Nikhils

On Fri, Mar 1, 2013 at 8:43 PM, Arni Sumarlidason
<Arn...@md...> wrote:
> Users,
>
>
>
> I have 20 nodes sitting on a disk arrays, with multiple LUNs. when I issue
> queries – `select count(1) from table` for example, I am experiencing heavy
> writes and heavy reads. I expected the reads but not the writes and it has
> really thrown a wrench in the caching. My first assumption would be the log
> files, do you have any other ideas what could be causing all these writes
> with a select?
>
>
>
> Arni Sumarlidason | Software Engineer, Information Technology
>
> MDA | 820 West Diamond Ave | Gaithersburg, MD | USA
>
> O: 240-833-8200 D: 240-833-8318 M: 256-393-2803
>
> arn...@md...| http://www.mdaus.com
>
>
>
>
> ------------------------------------------------------------------------------
> Everyone hates slow websites. So do we.
> Make your web apps faster with AppDynamics
> Download AppDynamics Lite for free today:
> http://p.sf.net/sfu/appdyn_d2d_feb
> _______________________________________________
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> Pos...@li...
> https://lists.sourceforge.net/lists/listinfo/postgres-xc-general
>



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Re: [Postgres-xc-developers] [Postgres-xc-general] IO PGXC

From: Mason S. <ma...@st...> - 2013-03-01 20:26:33

Sent from my IPhone

On Mar 1, 2013, at 4:13 PM, Arni Sumarlidason <Arn...@md...> wrote:

> Users,
>  
> I have 20 nodes sitting on a disk arrays, with multiple LUNs. when I issue queries – `select count(1) from table` for example, I am experiencing heavy writes and heavy reads. I expected the reads but not the writes and it has really thrown a wrench in the caching. My first assumption would be the log files, do you have any other ideas what could be causing all these writes with a select?

It could be vacuum. Also, did you just load data? Hint bits get updated, dirtying pages and causing them to be written.

>  
> Arni Sumarlidason | Software Engineer, Information Technology
> MDA | 820 West Diamond Ave | Gaithersburg, MD | USA
> O: 240-833-8200 D: 240-833-8318 M: 256-393-2803
> arn...@md...| http://www.mdaus.com 
>  
> ------------------------------------------------------------------------------
> Everyone hates slow websites. So do we.
> Make your web apps faster with AppDynamics
> Download AppDynamics Lite for free today:
> http://p.sf.net/sfu/appdyn_d2d_feb
> _______________________________________________
> Postgres-xc-general mailing list
> Pos...@li...
> https://lists.sourceforge.net/lists/listinfo/postgres-xc-general

Re: [Postgres-xc-developers] [Postgres-xc-general] IO PGXC

From: Arni S. <Arn...@md...> - 2013-03-01 20:19:33

Thank you for your fast responses,

We are running metrics on the system now, we loaded some data recently, and continuing to do so now. If Hint bits are the case, what steps can I take to relieve some of this IO?

From: Mason Sharp [mailto:ma...@st...]
Sent: Friday, March 01, 2013 2:29 PM
To: Arni Sumarlidason
Cc: pos...@li...; Postgres-XC Developers (pos...@li...)
Subject: Re: [Postgres-xc-general] IO PGXC

Sent from my IPhone

On Mar 1, 2013, at 4:13 PM, Arni Sumarlidason <Arn...@md...<mailto:Arn...@md...>> wrote:
Users,

I have 20 nodes sitting on a disk arrays, with multiple LUNs. when I issue queries – `select count(1) from table` for example, I am experiencing heavy writes and heavy reads. I expected the reads but not the writes and it has really thrown a wrench in the caching. My first assumption would be the log files, do you have any other ideas what could be causing all these writes with a select?

It could be vacuum. Also, did you just load data? Hint bits get updated, dirtying pages and causing them to be written.

Arni Sumarlidason | Software Engineer, Information Technology
MDA | 820 West Diamond Ave | Gaithersburg, MD | USA
O: 240-833-8200 D: 240-833-8318 M: 256-393-2803
arn...@md...<mailto:arn...@md...>| http://www.mdaus.com<https://console.mxlogic.com/redir/?4sMUMqenzhOqejrUVBxB4QsCzAS02lgRKDbUrLOrb0VVdOXMUTsSHJaM1l9RyGwgVsSYOYMrhpsjhsshpvdIICMnWhEwdbomHip6fQbxZyV7Uv7jPiWq80Qc6y0b181x8TfM-u0USyrpdIIczxNEVvsdD8rO>

------------------------------------------------------------------------------
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Make your web apps faster with AppDynamics
Download AppDynamics Lite for free today:
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Re: [Postgres-xc-developers] [Postgres-xc-general] IO PGXC

From: Nikhil S. <ni...@st...> - 2013-03-02 05:39:32

>
> We are running metrics on the system now, we loaded some data recently, and
> continuing to do so now. If Hint bits are the case, what steps can I take to
> relieve some of this IO?
>

This is internal IO which will settle down if you are not loading into
the same table again immediately. A lumpsum count(1) call (after a
recent data load) will touch all pages immediately, so try to avoid
that and amortize the IO over multiple specific select calls.

HTH,
Nikhils


>
>
> From: Mason Sharp [mailto:ma...@st...]
> Sent: Friday, March 01, 2013 2:29 PM
> To: Arni Sumarlidason
> Cc: pos...@li...; Postgres-XC Developers
> (pos...@li...)
> Subject: Re: [Postgres-xc-general] IO PGXC
>
>
>
>
> Sent from my IPhone
>
>
> On Mar 1, 2013, at 4:13 PM, Arni Sumarlidason <Arn...@md...>
> wrote:
>
> Users,
>
>
>
> I have 20 nodes sitting on a disk arrays, with multiple LUNs. when I issue
> queries – `select count(1) from table` for example, I am experiencing heavy
> writes and heavy reads. I expected the reads but not the writes and it has
> really thrown a wrench in the caching. My first assumption would be the log
> files, do you have any other ideas what could be causing all these writes
> with a select?
>
>
>
> It could be vacuum. Also, did you just load data? Hint bits get updated,
> dirtying pages and causing them to be written.
>
>
>
>
>
> Arni Sumarlidason | Software Engineer, Information Technology
>
> MDA | 820 West Diamond Ave | Gaithersburg, MD | USA
>
> O: 240-833-8200 D: 240-833-8318 M: 256-393-2803
>
> arn...@md...| http://www.mdaus.com
>
>
>
> ------------------------------------------------------------------------------
> Everyone hates slow websites. So do we.
> Make your web apps faster with AppDynamics
> Download AppDynamics Lite for free today:
> http://p.sf.net/sfu/appdyn_d2d_feb
>
> _______________________________________________
> Postgres-xc-general mailing list
> Pos...@li...
> https://lists.sourceforge.net/lists/listinfo/postgres-xc-general



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