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From: Bruce Momjian <bruce@momjian.us>
Message-Id: <201005101512.o4AFCZS27089@momjian.us>
Subject: Re: no universally correct setting for fsync
In-Reply-To: <4BE81CA1.4080201@partiallystapled.com>
To: Michael Tharp <gxti@partiallystapled.com>
Date: Mon, 10 May 2010 11:12:35 -0400 (EDT)
CC: Craig Ringer <craig@postnewspapers.com.au>, pgsql-hackers@postgresql.org
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Michael Tharp wrote:
> On 05/08/2010 04:07 AM, Craig Ringer wrote:
> > It's probably worth mentioning that people who want to turn off fsync to
> > gain a performance boost should instead look at a RAID controller with a
> > BBU so they can safely enable write-back caching, getting most of the
> > benefits of fsync=off safely.
> 
> Which options specifically should be set if a BBU is in use? Obviously 
> fsync should be on always, but can full_page_writes be disabled? Are 
> there other tweaks that can be done?
> 
> It would be great to see some practical hints in the documentation while 
> the fsync part is getting changed.

Uh, our docs have:

	Turning this parameter off speeds normal operation, but might
	lead to a corrupt database after an operating system crash or
	power failure. The risks are similar to turning off
	<varname>fsync</>, though smaller.  It might be safe to turn
	off this parameter if you have hardware (such as a battery-backed
	disk controller) or file-system software that reduces the risk
	of partial page writes to an acceptably low level (e.g., ZFS).

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com