Re: Faster CREATE DATABASE by delaying fsync (was 8.4.1 ubuntu karmic slow createdb)

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.

Andres