Re: [PERFORM] OS cache management

[Soni M]

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  wrote:

>
>
> - Mensaje original -
> > De: "Soni M" 
> > Para: pgsql-performance@postgresql.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

Re: [PERFORM] OS cache management

[Gerardo Herzig]

- Mensaje original -
> De: "Soni M" 
> Para: pgsql-performance@postgresql.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


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