To: Ron <rjpeace@earthlink.net>
cc: Steve <cheetah@tanabi.org>, pgsql-performance@postgresql.org
Subject: Re: Question about memory allocations 
In-reply-to: <E1HcQQa-0004MS-5s@elasmtp-masked.atl.sa.earthlink.net> 
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	<14019.1176155022@sss.pgh.pa.us>
	<22512E5C-A60F-43E7-A370-257F7AF956FD@gmail.com>
	<16374.1176171185@sss.pgh.pa.us>
	<D14BB823-DA04-453C-AD70-248B34F1307B@gmail.com>
	<25200.1176213242@sss.pgh.pa.us>
	<FCEF7DE2-913F-4C36-B117-8363EDE39BF3@gmail.com>
	<26925.1176221294@sss.pgh.pa.us>
	<Pine.GSO.4.64.0704101458290.17955@kittyhawk.tanabi.org>
	<1176453355.609.4.camel@hippy.mcmillan.net.nz>
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Comments: In-reply-to Ron <rjpeace@earthlink.net>
	message dated "Fri, 13 Apr 2007 14:23:08 -0400"
Date: Sat, 14 Apr 2007 12:37:54 -0400
Message-ID: <4918.1176568674@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Ron <rjpeace@earthlink.net> writes:
> One of the reasons for the wide variance in suggested values for pg 
> memory use is that pg 7.x and pg 8.x are =very= different beasts.
> If you break the advice into pg 7.x and pg 8.x categories, you find 
> that there is far less variation in the suggestions.
> Bottom line: pg 7.x could not take advantage of larger sums of memory 
> anywhere near as well as pg 8.x can.

Actually I think it was 8.1 that really broke the barrier in terms of
scalability of shared_buffers.  Pre-8.1, the buffer manager just didn't
scale well enough to make it useful to use more than a few hundred meg.
(In fact, we never even bothered to fix the shared-memory-sizing
calculations to be able to deal with >2GB shared memory until 8.1;
if you try it in 8.0 it'll probably just crash.)

			regards, tom lane