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Re: There is a statistic table?

From: Cédric Villemain <cedric(dot)villemain(at)dalibo(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Cc: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>, Scott Carey <scott(at)richrelevance(dot)com>, Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at>, "waldomiro *EXTERN*" <waldomiro(at)shx(dot)com(dot)br>
Subject: Re: There is a statistic table?
Date: 2009-10-22 11:04:57
Message-ID: 200910221305.03262.cedric.villemain@dalibo.com (view raw or flat)
Thread:
Lists: pgsql-performance
Le jeudi 22 octobre 2009 00:06:10, Scott Marlowe a écrit :
> On Wed, Oct 21, 2009 at 11:17 AM, Scott Carey <scott(at)richrelevance(dot)com> 
wrote:
> > On 10/15/09 11:27 PM, "Albe Laurenz" <laurenz(dot)albe(at)wien(dot)gv(dot)at> wrote:
> >> waldomiro wrote:
> >>> I need to know how much the postgres is going to disk to get
> >>> blocks and how much it is going to cache? witch is the
> >>> statistic table and what is the field that indicates blocks
> >>> reads from the disk and the memory cache?
> >>
> >> The view pg_statio_all_tables will show you the number of
> >> disk reads and buffer hits per table.
> >
> > My understanding is that it will not show that.  Since postgres can't
> > distinguish between a read that comes from OS cache and one that goes to
> > disk, you're out of luck on knowing anything exact.
> > The above shows what comes from shared_buffers versus the OS, however.
> >  And if reads are all buffered, they are not coming from disk.  Only
> > those that come from the OS _may_ have come from disk.
> 
> I think he meant pg's shared_buffers not the OS kernel cache.
> 

pgfincore let you know if block are in OS kernel cache  or not. 

-- 
Cédric Villemain
Administrateur de Base de Données
Cel: +33 (0)6 74 15 56 53
http://dalibo.com - http://dalibo.org

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