Date: Tue, 16 Mar 2010 18:49:03 -0300
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Greg Stark <gsstark@mit.edu>, Pierre C <lists@peufeu.com>,
	Greg Smith <greg@2ndquadrant.com>, Dave Crooke <dcrooke@gmail.com>,
	Paul McGarry <paul@paulmcgarry.com>, pgsql-performance@postgresql.org
Subject: Re: shared_buffers advice
Message-ID: <20100316214903.GH3037@alvh.no-ip.org>
References: <a056b1d41003101728h2bfe964cg43bf5ef1aabae14d@mail.gmail.com>
	<ca24673e1003152217q117b0fd3q7d2d75ff20185c8b@mail.gmail.com>
	<4B9F3302.4020900@2ndquadrant.com> <op.u9nrbeeteorkce@localhost>
	<8285.1268749832@sss.pgh.pa.us>
	<407d949e1003160753o6e5faa48rabaa42f7548029b7@mail.gmail.com>
	<20100316213054.GG3037@alvh.no-ip.org>
	<15102.1268775566@sss.pgh.pa.us>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <15102.1268775566@sss.pgh.pa.us>
User-Agent: Mutt/1.5.20 (2009-06-14)

Tom Lane escribió:
> Alvaro Herrera <alvherre@commandprompt.com> writes:
> > Maybe it would make more sense to try to reorder the fsync calls
> > instead.
> 
> Reorder to what, though?  You still have the problem that we don't know
> much about the physical layout on-disk.

Well, to block numbers as a first step.

However, this reminds me that sometimes we take the block-at-a-time
extension policy too seriously.  We had a customer that had a
performance problem because they were inserting lots of data to TOAST
tables, causing very frequent extensions.  I kept wondering whether an
allocation policy that allocated several new blocks at a time could be
useful (but I didn't try it).  This would also alleviate fragmentation,
thus helping the physical layout be more similar to logical block
numbers.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support