From: Jesper Krogh <jesper@krogh.cc>
To: Greg Smith <greg@2ndquadrant.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: jd@commandprompt.com, Scott Marlowe <scott.marlowe@gmail.com>
Cc: Steve Crawford <scrawford@pinpointresearch.com>
Cc: pgsql-performance@postgresql.org, Ben Chobot <bench@silentmedia.com>
Subject: Re: BBU Cache vs. spindles
Date: Fri, 22 Oct 2010 18:36:22 +0200
Message-ID: <4CC1BD86.8070006@krogh.cc> (raw)
In-Reply-To: <4CC1AFB3.3000903@2ndquadrant.com>
References: <4CC04EA50200002500036C5E@gw.wicourts.gov>
<201010211935.o9LJZTM21744@momjian.us>
<4CC0513E0200002500036C68@gw.wicourts.gov>
<4CC1094C.1090306@2ndquadrant.com>
<13038.1287720327@sss.pgh.pa.us>
<4CC1AFB3.3000903@2ndquadrant.com>
On 2010-10-22 17:37, Greg Smith wrote:
> I think that most people who have thought they were safe to turn off
> full_page_writes in the past did so because they believed they were
> in category (1) here. I've never advised anyone to do that, because
> it's so difficult to validate the truth of. Just given that, I'd be
> tempted to join in on suggesting this parameter just go away in the
> name of safety, except that I think category (2) here is growing now.
> ZFS is the most obvious example where the atomic write implementation
> seems to always make disabling full_page_writes safe.
Can you point to some ZFS docs that tell that this is the case.. I'd be
surprised
if it doesnt copy away the old block and replaces it with the new one
in-place. The
other behaviour would quite quickly lead to a hugely fragmented
filesystem that
performs next to useless and ZFS doesnt seem to be in that category..
... All given my total lack of insight into ZFS.
--
Jesper
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To: pgsql-performance@postgresql.org
Cc: jesper@krogh.cc, greg@2ndquadrant.com, tgl@sss.pgh.pa.us, Kevin.Grittner@wicourts.gov, bruce@momjian.us, scott.marlowe@gmail.com, scrawford@pinpointresearch.com, bench@silentmedia.com
Subject: Re: BBU Cache vs. spindles
In-Reply-To: <4CC1BD86.8070006@krogh.cc>
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