Subject: Re: Linux mis-reporting memory
From: Simon Riggs <simon@2ndquadrant.com>
To: Csaba Nagy <nagy@ecircle-ag.com>
Cc: Gregory Stark <stark@enterprisedb.com>, Decibel! <decibel@decibel.org>,
	pgsql-performance@postgresql.org
In-Reply-To: <1190369325.4661.178.camel@PCD12478>
References: <20070920230400.GM95343@decibel.org>
	<16213.1190329934@sss.pgh.pa.us> <87r6ksa1jb.fsf@oxford.xeocode.com>
	<1190363401.4661.116.camel@PCD12478>
	<87r6ksuzf8.fsf@oxford.xeocode.com>
	<1190369325.4661.178.camel@PCD12478>
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Date: Fri, 21 Sep 2007 12:01:18 +0100
Message-Id: <1190372478.4202.17.camel@ebony.site>
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On Fri, 2007-09-21 at 12:08 +0200, Csaba Nagy wrote:
> On Fri, 2007-09-21 at 10:43 +0100, Gregory Stark wrote:
> > The other possibility is that Postgres just hasn't even touched a large part
> > of its shared buffers. 
> > 
> 
> But then how do you explain the example I gave, with a 5.5GB table
> seq-scanned 3 times, shared buffers set to 12 GB, and top still showing
> almost 100% memory as cached and no SWAP "used" ? In this case you can't
> say postgres didn't touch it's shared buffers - or a sequential scan
> won't use the shared buffers ?

Well, 6.5GB of shared_buffers could be swapped out and need not be
swapped back in to perform those 3 queries.

-- 
  Simon Riggs
  2ndQuadrant  http://www.2ndQuadrant.com