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shared_buffers vs Linux file cache - Mailing list pgsql-performance

From Huan Ruan
Subject shared_buffers vs Linux file cache
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Msg-id CAD1stZv-iJUTRoMkj8xq_NdaNhrtHvjKO98wzEJAhf+TsgYdcA@mail.gmail.com
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Re: shared_buffers vs Linux file cache
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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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