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From: Peter Schuller <peter.schuller@infidyne.com>
To: David Rees <drees76@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Occasional Slow Commit
Date: Thu, 6 Nov 2008 11:21:47 +0100
Message-ID: <20081106102147.GB70379@hyperion.scode.org> (raw)
In-Reply-To: <72dbd3150811051925n50ead40cn30354990ebb8bfb6@mail.gmail.com>
References: <72dbd3150810271723w57859013v9c4e3718ae86fba@mail.gmail.com>
	<Pine.GSO.4.64.0810290906150.19233@westnet.com>
	<72dbd3150810291530q7a95da64j2c39354de9ad91d1@mail.gmail.com>
	<72dbd3150810311714s51639bc3kfdbe03a7b51bc55c@mail.gmail.com>
	<72dbd3150811051925n50ead40cn30354990ebb8bfb6@mail.gmail.com>

> I also found that my write cache was set to WriteThrough instead of
> WriteBack, defeating the purpose of having a BBU and that my secondary
> server apparently doesn't have a BBU on it. :-(

Note also that several RAID controllers will periodically drop the
write-back mode during battery capacity tests. If you care about
consistently/deterministically having full performance (with
white-backed battery protected caching), you probably want to confirm
your controller behavior here.

(I've seen this on at least LSI based controllers in Dell 2950:s, and
also on some 3wares.)

-- 
/ Peter Schuller

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