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Re: separate drives for WAL or pgdata files

From: "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>
To: David Lang <dlang(at)invendra(dot)net>
Cc: Anjan Dave <adave(at)vantage(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: separate drives for WAL or pgdata files
Date: 2005-12-20 19:52:20
Message-ID: 20051220195220.GK28771@pervasive.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Mon, Dec 19, 2005 at 07:20:56PM -0800, David Lang wrote:
> for persistant storage you can replicate from your ram-based system to a 
> disk-based system, and as long as your replication messages hit disk 
> quickly you can allow the disk-based version to lag behind in it's updates 
> during your peak periods (as long as it is able to catch up with the 
> writes overnight), and as the disk-based version won't have to do the 
> seeks for the reads it will be considerably faster then if it was doing 
> all the work (especially if you have good, large  battery-backed disk 
> caches to go with those drives to consolodate the writes)

Huh? Unless you're doing a hell of a lot of writing just run a normal
instance and make sure you have enough bandwidth to the drives with
pg_xlog on it. Make sure those drives are using a battery-backed raid
controller too. You'll also need to tune things to make sure that
checkpoints never have much (if any) work to do when the occur, but you
should be able to set that up with proper bg_writer tuning.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby(at)pervasive(dot)com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

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