Message-ID: <4BB32A0F.3000200@2ndquadrant.com>
Date: Wed, 31 Mar 2010 06:55:11 -0400
From: Greg Smith <greg@2ndquadrant.com>
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To: rodger@diaspora.gen.nz
CC: pgsql-admin@postgresql.org
Subject: Re: Virtualization vs. sharing a server
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	<64633.203.144.40.146.1269983303.squirrel@israel.diaspora.gen.nz>
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Rodger Donaldson wrote:
> On Tue, March 30, 2010 06:09, Greg Smith wrote:
>   
>> You answered your own question here.  Ramiro is looking for suggestions
>> for how to scale up to >500 connections at once, and it's not that
>> likely virtualization can fill any useful role in that context.
>>     
>
> That rather depends on your virtualisation layer.  We haven't run large PG
> databases on our zLinux/zVM machines, but we have Oracle DBs running
> comparable connection numbers without any issues.
>   

Connection scaling in Oracle doesn't have the same characteristics as 
PostgreSQL, so you can't extrapolate from that.  My point was that the 
connection target here would be aggressive and difficult to achieve even 
without virtualization involved.  The virtualization sofware used will 
impact the exact percentage of overhead involved, but you'd be hard 
pressed to get this to work as hoped even if that number were 0--so 
anything >0, even small, is increasing the odds of failure.

-- 
Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com   www.2ndQuadrant.us