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From: Carlos Moreno <moreno_pg@mochima.com>
To: pgsql-performance@postgresql.org
Subject: Re: Question about memory allocations
Date: Fri, 13 Apr 2007 14:53:53 -0400
Message-ID: <461FD1C1.8040502@mochima.com> (raw)
In-Reply-To: <Pine.GSO.4.64.0704131229230.17955@kittyhawk.tanabi.org>
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	<14019.1176155022@sss.pgh.pa.us>
	<22512E5C-A60F-43E7-A370-257F7AF956FD@gmail.com>
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	<26925.1176221294@sss.pgh.pa.us>
	<Pine.GSO.4.64.0704101458290.17955@kittyhawk.tanabi.org>
	<1176453355.609.4.camel@hippy.mcmillan.net.nz>
	<Pine.GSO.4.64.0704131229230.17955@kittyhawk.tanabi.org>

Steve wrote:
>>
>> Common wisdom in the past has been that values above a couple of hundred
>> MB will degrade performance.  

The annotated config file talks about setting shared_buffers to a third 
of the
available memory --- well, it says "it should be no more than 1/3 of the 
total
amount of memory"  (quoting off the top of my head).  Don't recall seeing
any warning about not exceeding a few hundred megabytes.

My eternal curiosity when it comes to this memory and shared_buffers thing:

How does PG take advantage of the available memory?  I mean, if I have a
machine with, say, 4 or 8GB of memory, how will those GBs would end
up being used?   They just do??   (I mean, I would find that a vaild 
answer;
but I ask, because this configuration parameters stuff makes me think that
perhaps PG does not simply use whatever memory is in there, but it has
to go through the parameters in the config file to allocate whatever it has
to use).

So, is it just like that?   We put more memory and PG will automatically
make use of it?

Carlos
--




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