From owner-freebsd-database@FreeBSD.ORG  Fri Jul 25 01:55:58 2003
Return-Path: <owner-freebsd-database@FreeBSD.ORG>
Delivered-To: freebsd-database@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP
	id 8F30537B401; Fri, 25 Jul 2003 01:55:58 -0700 (PDT)
Received: from misery.sdf.com (misery.sdf.com [207.200.153.226])
	by mx1.FreeBSD.org (Postfix) with ESMTP
	id 400F043F3F; Fri, 25 Jul 2003 01:55:56 -0700 (PDT)
	(envelope-from tom@sdf.com)
Received: from tom (helo=localhost)
	by misery.sdf.com with local-esmtp (Exim 2.12 #1)
	id 19fwc6-0004gx-00; Fri, 25 Jul 2003 00:03:38 -0700
Date: Fri, 25 Jul 2003 00:03:32 -0700 (PDT)
From: Tom Samplonius <tom@sdf.com>
To: Christopher Weimann <csw@k12hq.com>
In-Reply-To: <20030724173910.GA9364@smtp.k12us.com>
Message-ID: <Pine.BSF.4.05.10307242358580.16986-100000@misery.sdf.com>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
cc: Sean Chittenden <seanc@FreeBSD.org>
cc: freebsd-database@freebsd.org
cc: freebsd-performance@freebsd.org
cc: Terry Lambert <tlambert2@mindspring.com>
cc: Paul Pathiakis <paul@pathiakis.com>
Subject: Re: Tuning for PostGreSQL Database
X-BeenThere: freebsd-database@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Database use and development under FreeBSD
	<freebsd-database.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-database>,
	<mailto:freebsd-database-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-database>
List-Post: <mailto:freebsd-database@freebsd.org>
List-Help: <mailto:freebsd-database-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-database>,
	<mailto:freebsd-database-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 25 Jul 2003 08:55:59 -0000


On Thu, 24 Jul 2003, Christopher Weimann wrote:

...
> So if PostGreSQL uses fsync when writing ( which I think is only true
> on the write-ahead logs at this point ) that data will NOT wind up in 
> the cache.  Anything that PostGreSQL reads should wind up in the cache?
> 
> #uname -r
> 4.7-RELEASE-p3
> 
> # top -b | head -5
> last pid: 58622;  load averages:  1.96,  1.67,  1.47  up 2+12:59:15    13:31:39
> 130 processes: 6 running, 124 sleeping
> 
> Mem: 348M Active, 2628M Inact, 438M Wired, 155M Cache, 380M Buf, 76M Free
> Swap: 4096M Total, 28K Used, 4096M Free
> 
> The 2628M Inact is likley to be acting as cache?
> 
> Basically I should stop worrying about this :)


  Maybe you should continue to worry.  PostgreSQL isn't MySQL (or a
typical server application).  It reads all database pages into its shared
memory area.  It is wasteful for the DBMS and the OS to both cache this
data.  You'll want the PostgreSQL shared memory size to be around 75% the
size of RAM (on a dedicated DBMS server).  In fact, many commercial DBMS
systems will use raw writes to bypass the OS cache!

Tom