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From: Greg Smith <greg@2ndquadrant.com>
To: Andy Colson <andy@squeakycode.net>
Cc: Craig Ringer <craig@postnewspapers.com.au>
Cc: pgsql-performance@postgresql.org
Subject: Re: a heavy duty operation on an "unused" table kills my server
Date: Thu, 14 Jan 2010 13:30:46 -0500
Message-ID: <4B4F62D6.7020104@2ndquadrant.com> (raw)
In-Reply-To: <4B4F5F45.105@squeakycode.net>
References: <e24c1d9d1001122059ic5d4721o98ccf85033b1fead@mail.gmail.com>
	<4B4D5698.8040808@emolecules.com>
	<e24c1d9d1001122147l1c0e2111kce25dc2c7f393087@mail.gmail.com>
	<4B4D61DA.7080008@postnewspapers.com.au>
	<e24c1d9d1001122303g1d4eea48h18bd73467d1fa8ec@mail.gmail.com>
	<603c8f071001130823l69804fe3m5c6fbb081c55c265@mail.gmail.com>
	<4B4EAD76.9030305@postnewspapers.com.au>
	<4B4F2F00.7070401@squeakycode.net>
	<4B4F5D70.4020103@2ndquadrant.com>
	<4B4F5F45.105@squeakycode.net>

Andy Colson wrote:
> So if there is very little io, or if there is way way too much, then 
> the scheduler really doesn't matter.  So there is a slim middle ground 
> where the io is within a small percent of the HD capacity where the 
> scheduler might make a difference?

That's basically how I see it.  There seem to be people who run into 
workloads in the middle ground where the scheduler makes a world of 
difference.  I've never seen one myself, and suspect that some of the 
reports of deadline being a big improvement just relate to some buginess 
in the default CFQ implementation that I just haven't encountered.

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




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