Re: How to find if a SELECT is reading from buffer or disk ?

I am on Fedora 12 (x86_64). Will eventually be on RHE.

> Date: Tue, 25 May 2010 12:59:16 -0500
> From: Kevin(dot)Grittner(at)wicourts(dot)gov
> To: b_ki(at)hotmail(dot)com; pgsql-admin(at)postgresql(dot)org
> Subject: Re: [ADMIN] How to find if a SELECT is reading from buffer or disk ?
>
> Balkrishna Sharma <b_ki(at)hotmail(dot)com> wrote:
>
> > I am increasing the shared_buffer size in postgresql.conf and want
> > to measure its effect on READ. In essence I want to know if the
> > SELECT queries I am firing repeatedly is reading from the buffer
> > or going directly to the disk.
>
> There's a third option -- PostgreSQL reads and writes will normally
> go through the OS cache.
>
> > Right now I am just looking at execution time of the SELECTs and
> > trying to conclude. But there should be a direct way to see where
> > the SELECT reads from.
> > How can I accomplish this ?
>
> You didn't mention your OS. There's usually a way to monitor disk
> I/O built in to the OS. I usually start with:
>
> vmstat 1
>
> -Kevin
>
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