Re: Improvement of checkpoint IO scheduler for stable transaction responses

On Wed, Jul 17, 2013 at 1:54 PM, Greg Smith <greg@2ndquadrant.com> wrote:
> On 7/16/13 11:36 PM, Ants Aasma wrote:
>>
>> As you know running a full suite of write benchmarks takes a very long
>> time, with results often being inconclusive (noise is greater than
>> effect we are trying to measure).
>
>
> I didn't say that.  What I said is that over a full suite of write
> benchmarks, the effect of changes like this has always averaged out to zero.
> You should try it sometime.  Then we can have a useful discussion of
> non-trivial results instead of you continuing to tell me I don't understand
> things.

The fact that other changes have been tradeoffs doesn't change the
point that there is no tradeoff here. I see no way in which writing
blocks to the OS in a logical order is worse than writing them out in
arbitrary order. This is why I considered blindly running write
benchmarks a waste of time at this point - if the worst case is zero
and there are cases where it helps then it can't average out to zero.
It would be better to identify the worst case and design a test for
that.

However I started the full gamut of scale factors and client count
tests just do quiet any fears of unexpected regressions. 4 scales, 6
client loads, 3 tests, 20min per test, 2 versions, the results will be
done in 48h.

Regards,
Ants Aasma
--
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt
Web: http://www.postgresql-support.de