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Re: Limited Shared Buffer Problem

From: Greg Smith <greg(at)2ndquadrant(dot)com>
To: Cédric Villemain <cedric(dot)villemain(dot)debian(at)gmail(dot)com>
Cc: Richard Neill <rn214(at)cam(dot)ac(dot)uk>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Limited Shared Buffer Problem
Date: 2010-01-29 22:19:41
Message-ID: 4B635EFD.7000403@2ndquadrant.com (view raw or flat)
Thread:
Lists: pgsql-performance
Cédric Villemain wrote:
> AFAIK effective_cache_size is estimation of OS Page Cache + Estimated
> Cache in shared_buffers.
>   

Yes, the total value you set is used as is, and should include both 
pieces of memory.  The planner doesn't add the shared_buffers value to 
the total first for you, as some people might guess it would. 

The only thing effective_cache_size is used for is estimating how 
expensive an index is likely to be to use, to make decisions like when 
to do an index-based scan instead of just scanning the table itself.

-- 
Greg Smith    2ndQuadrant   Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com  www.2ndQuadrant.com


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