Re: OS cache management

----- 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