From: Andres Freund <andres@anarazel.de>
To: pgsql-performance@postgresql.org
Cc: Scott Marlowe <scott.marlowe@gmail.com>
Cc: Richard Shaw <richard@aggress.net>
Cc: Andy Colson <andy@squeakycode.net>
Subject: Re: Rather large LA
Date: Tue, 6 Sep 2011 16:51:17 +0200
Message-ID: <201109061651.18111.andres@anarazel.de> (raw)
In-Reply-To: <CAOR=d=2WjEiFhbAL4f7EZi38ZeDSexdnhD_EEcgsPd8A8fwc7w@mail.gmail.com>
References: <F757E48F-2B4F-496D-951B-B04ED98F8FD6@aggress.net>
<1894838.pasMZSmQAq@alap2>
<CAOR=d=2WjEiFhbAL4f7EZi38ZeDSexdnhD_EEcgsPd8A8fwc7w@mail.gmail.com>
On Monday 05 Sep 2011 22:23:32 Scott Marlowe wrote:
> On Mon, Sep 5, 2011 at 11:24 AM, Andres Freund <andres@anarazel.de> wrote:
> > On Monday, September 05, 2011 14:57:43 Richard Shaw wrote:
> >> Autovacuum has been disabled and set to run manually via cron during a
> >> quiet period and fsync has recently been turned off to gauge any real
> >> world performance increase, there is battery backup on the raid card
> >> providing some level of resilience.
> >
> > That doesn't help you against a failure due to fsync() off as the BBU can
> > only protect data that actually has been written to disk. Without
> > fsync=on no guarantee about that exists.
>
> Further, if you've got a bbu cache on the RAID card the gains from
> fsync=off wll be low / nonexistent.
Thats not necessarily true. If you have a mixed load of many small writes and
some parallel huge writes (especially in combination with big indexes)
fsync=off still can give you quite big performance increases. Even in the
presenence of synchronous_commit=off.
Andres
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To: pgsql-performance@postgresql.org
Cc: andres@anarazel.de, scott.marlowe@gmail.com, richard@aggress.net, andy@squeakycode.net
Subject: Re: Rather large LA
In-Reply-To: <201109061651.18111.andres@anarazel.de>
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