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Re: Setting Shared Buffers , Effective Cache, Sort Mem

From: Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com>
To: Manfred Koizar <mkoi-pg(at)aon(dot)at>
Cc: Pallav Kalva <pkalva(at)deg(dot)cc>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Setting Shared Buffers , Effective Cache, Sort Mem
Date: 2004-04-23 22:10:20
Message-ID: Pine.LNX.4.58.0404231506310.5473@one (view raw or flat)
Thread:
Lists: pgsql-performance
On Fri, 23 Apr 2004, Manfred Koizar wrote:
>
> Setting shared_buffers to half your available memory is the worst thing
> you can do.  You would end up caching exactly the same set of blocks in
> the internal buffers and in the OS cache, thus effectively making one of
> the caches useless.

One minor detail...  You wouldn't really cache the _exact_ same blocks
because cache-hits in shared-buffers (on the most frequently accessed
pages) would let the OS cache some other pages in it's cache.

But in my experience Manfred's right that there's no benefit and
some penalty to making shared_buffers so large it takes a significant
piece away from the OS's caching.

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