Subject: Re: PG on NFS may be just a bad idea
From: Simon Riggs <simon@2ndquadrant.com>
To: Josh Berkus <josh@agliodbs.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers@postgreSQL.org,
	pgsql-novice@postgreSQL.org, Mija Lee <mija@scharp.org>
In-Reply-To: <47012AC5.9040808@agliodbs.com>
References: <25517.1191038302@sss.pgh.pa.us> <47012AC5.9040808@agliodbs.com>
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Date: Mon, 01 Oct 2007 19:36:54 +0100
Message-Id: <1191263814.4260.57.camel@ebony.site>
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On Mon, 2007-10-01 at 10:13 -0700, Josh Berkus wrote:

> > Maybe we need to actively discourage people from running Postgres
> > against NFS-mounted data directories.  Shane Kerr's paper cited above
> > mentions some other rather scary properties, including O_EXCL file
> > creation not really working properly.
> 
> Wouldn't you be describing a Linux-specific issue, though?  And possibly 
> kernel-specific?

Possibly, though if you have any specific refutations of the Kerr paper
then it would be a good idea to air them. It isn't enough to just hint
some exist.

> It's hard to reconcile this with the real-world performance of 
> PostgreSQL on NFS, which is happening all over the place.  Most notably, 
> Joe Conway's 20,000 txn/sec.
> 
> I *do* think it's an accurate statement that if you're going to use 
> Postgres, or any other OLTP database, on NFS you'd better have access to 
> a NAS expert.  But to say that it's a bad idea even if you have expert 
> help is probably going to far.

I can see many papers on database performance on NFS, but I don't see
any discussion of potential reliability concerns. If anybody sits near
an NAS expert, it would be great to have that discussion.

I have found some comments that other databases require "specific
configuration settings to ensure efficient and correct usage" of NFS "to
access NAS storage devices". 

-- 
  Simon Riggs
  2ndQuadrant  http://www.2ndQuadrant.com