Re: gaussian distribution pgbench

Hi,

(2014/03/14 4:21), Fabien COELHO wrote:
>
>> We should do the same discussion for the UI of command-line option? The patch
>> adds two options --gaussian and --exponential, but this UI seems to be a bit
>> inconsistent with the UI for \setrandom.
>> Instead, we can use something like --distribution=[uniform | gaussian |
>> exponential].
>
> Hmmm. That is possible, obviously.
>
> Note that it does not need to resort to a custom script, if one can do something
> like "--define=exp_threshold=5.6".
Yeah, threshold paramter should be needed by generating distribution algorithms
in my patch. And it is important that we can control distribution pattern by this
paramter.

> If so, maybe one simpler named variable could
> be used, say "threshold", instead of separate names for each options.
If we separate threshold option, I think it is difficult to understand dependency
of this parameter. Because "threshold" is very general term, and
when we will add other new feature, it is difficult to undestand which parameter
is dependent and be needed.

> However there is a catch: currently the option allows to check that the threshold
> is large enough so as to avoid loops in the generator. So this mean moving the
> check in the generator, and doing it over and over. Possibly this is a good idea,
> because otherwise a custom script could circumvent the check. Well, the current
> status is that the check can be avoided with --define...
>
> Also, a shorter possibly additional name, would be nice, maybe something like:
> --dist=exp|gauss|uniform? Not sure. I like long options not to be too long.
Well, if we run standard benchmark in pgbench, we need not set option because it
is default benmchmark, and it is same as uniform distribution. And if we run
extra benchmarks in pgbench which are like '-S' or '-N', we need to set option.
Because they are non-standard benchmark setting, and it is same as gaussian or
exponential distribution. So present UI keeps consistency and along the pgbench
history.

> I like long options not to be too long.
Yes, I like so too. Present UI is very simple and useful for combination using
such like '-S' and '--gaussian'. So I hope not changing UI.

ex)
pgbench -S --gaussian=5
pgbench -N --exponential=2 --sampling-rate=0.8

Regards,
--
Mitsumasa KONDO
NTT Open Source Software Center