shared_buffers vs Linux file cache

From: Huan Ruan <huan(dot)ruan(dot)it(at)gmail(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: shared_buffers vs Linux file cache
Date: 2015-01-15 11:30:55
Message-ID: CAD1stZv-iJUTRoMkj8xq_NdaNhrtHvjKO98wzEJAhf+TsgYdcA@mail.gmail.com
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Hi All

I thought 'shared_buffers' sets how much memory that is dedicated to
PostgreSQL to use for caching data, therefore not available to other
applications.

However, as shown in the following screenshots, The server (CentOS 6.6
64bit) has 64GB of RAM, and 'shared_buffer' is set to 32GB, but the
free+buffer+cache is 60GB.

Shouldn't the maximum value for free+buffer+cache be 32GB ( 64 - 32)?
Is 'shared_buffers' pre allocated to Postgres, and Postgres only?

Thanks
Huan

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[image: Inline images 1]

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