Re: OS cache management

In our environment, OS cache is much bigger than postgres buffers. Postgres
buffers around 8 GB, OS cache more than 100 GB. Maybe we should inspect
pgfincore

On Wed, Sep 6, 2017 at 9:13 PM, Gerardo Herzig <gherzig(at)fmed(dot)uba(dot)ar> wrote:

>
>
> ----- Mensaje original -----
> > De: "Soni M" <diptatapa(at)gmail(dot)com>
> > Para: pgsql-performance(at)postgresql(dot)org
> > Enviados: Miércoles, 6 de Septiembre 2017 5:12:26
> > Asunto: [PERFORM] OS cache management
> >
> > Hello All, I would like to know about how OS cache works for postgres
> table
> > and index file.
> >
> > Let's say I have 10 year data, and commonly used data only the last 1
> year.
> > This data is quite big, so each table and index file is divided into
> > several file in PGDATA/base
> >
> > Let's say 1 index named order_by_date has relfilenode = 1870772348, and
> > it's file consist of 1870772348, 1870772348.1, and 1870772348.2
> >
> > And for oftenly queried 1 year data, do ALL files for the order_by_date
> > pushed to OS cache ? or it's just 1 file that contains index to this 1
> year
> > data.
> >
>
> Postgres has its own cache (defined by the "shared_buffers" variable).
> Usually, the unit of movement in and out from the cache is a 8k page
> (defined at compilation time), so you cant put it directly in terms of
> files.
>
> There is an extension that can inspect the cache contents:
> https://www.postgresql.org/docs/current/static/pgbuffercache.html
>
> HTH
> Gerardo
>

--
Regards,

Soni Maula Harriz