Date: Wed, 29 Aug 2007 16:21:53 -0400
From: Bill Moran <wmoran@collaborativefusion.com>
To: Mark Mielke <mark@mark.mielke.cc>
Cc: mbguy2000-1@yahoo.com, pgsql-performance@postgresql.org
Subject: Re: Transaction Log
Message-Id: <20070829162153.cc48bced.wmoran@collaborativefusion.com>
In-Reply-To: <46D5CEDD.5010303@mark.mielke.cc>
References: <782718.73151.qm@web31603.mail.mud.yahoo.com>
	<46D5CEDD.5010303@mark.mielke.cc>
Organization: Collaborative Fusion
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In response to Mark Mielke <mark@mark.mielke.cc>:

> mbguy2000-1@yahoo.com wrote:
> > For best performance, the transaction log should be on a separate disk.
> >
> > Does the writing of the log benefit from a battery backed controller 
> > as well?  If not, what do people think about writing the transaction 
> > log to a flash card or the like?

Flash cards write _very_ slowly.

> How popular are the battery backed RAM drives that exist today? I don't 
> recall seeing them spoken about in this mailing list. The local geek 
> shop has these devices on sale. Are they still too expensive?

I've seen them around and as best I can tell, they're pretty
inexpensive.  The main drawback is the storage, you'd be looking at
the price of the card, plus the price of however much RAM you wanted
on it.

http://www.amazon.com/Gigabyte-GC-RAMDISK-i-RAM-Hard-Drive/dp/B000EPM9NC/ref=pd_bbs_sr_1/102-3968336-1618519?ie=UTF8&s=electronics&qid=1188418613&sr=8-1
http://techreport.com/articles.x/9312/1
Up to 4G, but you have to add the price of the RAM on to the price of
the card.

In the case of WAL logs, you could probably get away with a lot less
space than many other usages, so they might be very practical.

-- 
Bill Moran
Collaborative Fusion Inc.
http://people.collaborativefusion.com/~wmoran/

wmoran@collaborativefusion.com
Phone: 412-422-3463x4023