Re: 8.4.1 ubuntu karmic slow createdb - Mailing list pgsql-performance

On Sat, 2009-12-12 at 01:19 +0100, Andres Freund wrote:
> Hi,
>
> On Saturday 12 December 2009 00:59:13 Scott Marlowe wrote:
> > On Fri, Dec 11, 2009 at 3:52 PM, Michael Clemmons
> > >  Createdb takes
> > > 12secs on my system(9.10 pg8.4 and ext4)  which is impossibly slow for
> > > running 200unittests.
> > >  Fsync got it to .2secs or so which is blazing but
> > > also the speed I expected being used to 8.3 and xfs.  This dev box is my
> > > laptop and the data is litterally unimportant and doesn't exist longer
> > > than 20sec but Im all about good practices.  Will definately try
> > > synchronous commit tonight once Im done working for the day.  I've got
> > > some massive copying todo later though so this will probably help in the
> > > future as well.
> > Yeah, I'd probably resort to fsync off in that circumstance too
> > especially if syn commit off didn't help that much.
>
> How should syn commit help with creating databases?

It does not help here. Tested ;)

> The problem with 8.4 and creating databases is that the number of files
> increased hugely because of the introduction of relation forks.

Plus the fact that fsync on ext4 is really slow. some info here:
http://ldn.linuxfoundation.org/article/filesystems-data-preservation-fsync-and-benchmarks-pt-3

> It probably wouldnt be that hard to copy all files first, then reopen and fsync
> them. Actually that should be a patch doable in an hour or two.

Probably something worth doing, as it will speed this up on all
filesystems, and doubly so on ext4 and xfs.

--
Hannu Krosing   http://www.2ndQuadrant.com
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