From: Andres Freund <andres@anarazel.de>
To: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Faster CREATE DATABASE by delaying fsync (was 8.4.1
	ubuntu karmic slow createdb)
Date: Tue, 29 Dec 2009 19:30:49 +0100
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Cc: pgsql-performance@postgresql.org,
	Michael Clemmons <glassresistor@gmail.com>,
	Hannu Krosing <hannu@2ndquadrant.com>,
	Scott Marlowe <scott.marlowe@gmail.com>
References: <4427a97a0912101235x3ade510blcc00d5ce9883c6b6@mail.gmail.com>
	<200912282354.51892.andres@anarazel.de>
	<200912282359.43979.andres@anarazel.de>
In-Reply-To: <200912282359.43979.andres@anarazel.de>
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Message-Id: <200912291930.50812.andres@anarazel.de>

On Monday 28 December 2009 23:59:43 Andres Freund wrote:
> On Monday 28 December 2009 23:54:51 Andres Freund wrote:
> > On Saturday 12 December 2009 21:38:41 Andres Freund wrote:
> > > On Saturday 12 December 2009 21:36:27 Michael Clemmons wrote:
> > > > If ppl think its worth it I'll create a ticket
> > >
> > > Thanks, no need. I will post a patch tomorrow or so.
> >
> > Well. It was a long day...
> >
> > Anyway.
> > In this patch I delay the fsync done in copy_file and simply do a second
> >  pass over the directory in copy_dir and fsync everything in that pass.
> > Including the directory - which was not done before and actually might be
> > necessary in some cases.
> > I added a posix_fadvise(..., FADV_DONTNEED) to make it more likely that
> > the copied file reaches storage before the fsync. Without the speed
> > benefits were quite a bit smaller and essentially random (which seems
> > sensible).
> >
> > 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.
> >
> > The benefits are obviously bigger if the template database includes
> >  anything added.
> 
> Obviously the patch would be helpfull.
And it should also be helpfull not to have annoying oversights in there. A 	
FreeDir(xldir); is missing at the end of copydir().

Andres