Date: Tue, 04 Apr 2006 14:10:25 +1200
From: Mark Kirkwood <markir@paradise.net.nz>
Subject: Re: freebsd/softupdates for data dir
In-reply-to: <4431C4B4.4090300@123.com.sv>
To: Miguel <mmiranda@123.com.sv>
Cc: pgsql-performance@postgresql.org
Message-id: <4431D591.30500@paradise.net.nz>
MIME-version: 1.0
Content-type: text/plain; format=flowed; charset=ISO-8859-1
Content-transfer-encoding: 7bit
User-Agent: Mozilla Thunderbird 1.0.6 (X11/20051106)
References: <4431C4B4.4090300@123.com.sv>

Miguel wrote:
> Hi, reading the archives i cant find a clear answer about softupdates in 
> freebsd, is it recommended to enable it for the data directory?
> 

There is a pretty good article about softupdates and journelling here:

http://www.usenix.org/publications/library/proceedings/usenix2000/general/full_papers/seltzer/seltzer_html/index.html

and in the freebsd docs here:

http://www.freebsd.org/doc/handbook/configtuning-disk.html

Postgres does not do a lot of file meta-data operations (unless you do a 
*lot* of CREATE/DROP INDEX/TABLE/DATABASE), so the performance gains 
associated with softupdates will probably be minimal.

I've always left them on, and never had any issues...(even after 
unscheduled power loss - which happened here yesterday). As I understand 
it, the softupdate code reorders *metadata* operations, and does not 
alter data operations - so the effect of fysnc(2) on a preexisting file 
is not changed by softupdates being on or off.

Cheers

Mark