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Re: fsync and battery-backed caches

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>
Cc: Tino Wildenhain <tino(at)wildenhain(dot)de>, Javier Somoza <jsomoza(at)pandasoftware(dot)es>, pgsql-performance(at)postgresql(dot)org
Subject: Re: fsync and battery-backed caches
Date: 2006-02-28 01:06:13
Message-ID: 200602280106.k1S16DK16068@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Jim C. Nasby wrote:
> On Mon, Feb 27, 2006 at 11:12:57AM +0100, Tino Wildenhain wrote:
> > Javier Somoza schrieb:
> > >
> > >        Hi all
> > >
> > >        Is it secure to disable fsync havin battery-backed disk cache?
> > >               
> > >        Thx
> > >
> > No. fsync moves the data from OS memory cache to disk-adaptor
> > cache which is required to benefit from battery backup.
> 
> More importantly, in guarantees that data is committed to non-volatile
> storage in such a way that PostgreSQL can recover from a crash without
> corruption.
> 
> If you have a battery-backed controller and turn on write caching you
> shouldn't see much effect from fsync anyway.

We do mention battery-backed cache in our docs:

	http://www.postgresql.org/docs/8.1/static/wal.html

If it is unclear, please let us know.

-- 
  Bruce Momjian   http://candle.pha.pa.us
  SRA OSS, Inc.   http://www.sraoss.com

  + If your life is a hard drive, Christ can be your backup. +

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