From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Subject: Re: [HACKERS] Faster CREATE DATABASE by delaying fsync (was 8.4.1
	ubuntu karmic slow createdb)
Date: Tue, 29 Dec 2009 00:31:56 +0100
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Cc: pgsql-performance@postgresql.org, pgsql-hackers@postgresql.org,
	Michael Clemmons <glassresistor@gmail.com>,
	Hannu Krosing <hannu@2ndquadrant.com>,
	Scott Marlowe <scott.marlowe@gmail.com>
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	<200912282354.51892.andres@anarazel.de>
	<3454.1262041588@sss.pgh.pa.us>
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Message-Id: <200912290031.57136.andres@anarazel.de>

On Tuesday 29 December 2009 00:06:28 Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > This speeds up CREATE DATABASE from ~9 seconds to something around 0.8s
> > on my laptop.  Still slower than with fsync off (~0.25) but quite a
> > worthy improvement.
> 
> I can't help wondering whether that's real or some kind of
> platform-specific artifact.  I get numbers more like 3.5s (fsync off)
> vs 4.5s (fsync on) on a machine where I believe the disks aren't lying
> about write-complete.  It makes sense that an fsync at the end would be
> a little bit faster, because it would give the kernel some additional
> freedom in scheduling the required I/O, but it isn't cutting the total
> I/O required at all.  So I find it really hard to believe a 10x speedup.
I only comfortably have access to two smaller machines without BBU from here 
(being in the Hacker Jeopardy at the ccc congress ;-)) and both show this 
behaviour. I guess its somewhat filesystem dependent. 

Andres