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