Re: Testing Sandforce SSD

On Mon, Jul 26, 2010 at 03:23:20PM -0600, Greg Spiegelberg wrote:
> On Mon, Jul 26, 2010 at 1:45 PM, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
> > Yeb Havinga wrote:
> >> I did some ext3,ext4,xfs,jfs and also ext2 tests on the just-in-memory
> >> read/write test. (scale 300) No real winners or losers, though ext2 isn't
> >> really faster and the manual need for fix (y) during boot makes it
> >> impractical in its standard configuration.
> >>
> >
> > That's what happens every time I try it too. The theoretical benefits of
> > ext2 for hosting PostgreSQL just don't translate into significant
> > performance increases on database oriented tests, certainly not ones that
> > would justify the downside of having fsck issues come back again. Glad to
> > see that holds true on this hardware too.
> I know I'm talking development now but is there a case for a pg_xlog block
> device to remove the file system overhead and guaranteeing your data is
> written sequentially every time?
For one I doubt that its a relevant enough efficiency loss in
comparison with a significantly significantly complex implementation
(for one you cant grow/shrink, for another you have to do more
complex, hw-dependent things like rounding to hardware boundaries,
page size etc to stay efficient) for another my experience is that at
a relatively low point XlogInsert gets to be the bottleneck - so I
don't see much point in improving at that low level (yet at least).

Where I would like to do some hw dependent measuring (because I see
significant improvements there) would be prefetching for seqscan,
indexscans et al. using blktrace... But I currently dont have the
time. And its another topic ;-)

Andres