Re: fsync and battery-backed caches

[Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>]

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. +