Message-ID: <4AFBAF87.7060405@2ndquadrant.com>
Date: Thu, 12 Nov 2009 01:47:35 -0500
From: Greg Smith <greg@2ndquadrant.com>
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To: Scott Carey <scott@richrelevance.com>
CC: Craig James <craig_james@emolecules.com>,
	"pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Subject: Re: limiting performance impact of wal archiving.
References: <C720ED0E.167A3%scott@richrelevance.com>
In-Reply-To: <C720ED0E.167A3%scott@richrelevance.com>
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Scott Carey wrote:
>> Using ext2 means that you're still exposed to fsck errors on boot after
>> a crash, which doesn't lose anything but you have to go out of your way
>> to verify you're not going to get stuck with your server down in that
>> case.
> fsck on a filesystem with 1 folder and <checkpoint_segments> files is very
> very fast.  Even if using WAL archiving, there won't be many
> files/directories to check.  Fsck is not an issue if the partition is
> exclusively for WAL.  You can even mount it direct, and avoid having the OS
> cache those pages if you are using a caching raid controller
Right; that sort of thing--switching to a more direct mount, making sure 
fsck is setup to run automatically rather than dropping to a menu--is 
what I was alluding to when I said you had to go out of your way to make 
that work.  It's not complicated, really, but by the time you've set 
everything up and done the proper testing to confirm it all worked as 
expected you've just spent a modest chunk of time.  All I was trying to 
suggest is that there is a cost and some complexity, and that I feel 
there's no reason to justify that unless you're not bottlenecked 
specifically at WAL write volume.

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