Re: gaussian distribution pgbench

I have checked your v13 patch, and tested the new exponential distribution
generating algorithm. It works fine and less or no overhead than previous version.

Great work! And I agree with your proposal.

And I'm also interested in your "decile percents" output like under followings,

> [nttcom@localhost postgresql]$ contrib/pgbench/pgbench --exponential=20
> ~
> decile percents: 86.5% 11.7% 1.6% 0.2% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
> ~
> [nttcom@localhost postgresql]$ contrib/pgbench/pgbench --exponential=10
> ~
> decile percents: 63.2% 23.3% 8.6% 3.1% 1.2% 0.4% 0.2% 0.1% 0.0% 0.0%
> ~
> [nttcom@localhost postgresql]$ contrib/pgbench/pgbench --exponential=5
> ~
> decile percents: 39.6% 24.0% 14.6% 8.8% 5.4% 3.3% 2.0% 1.2% 0.7% 0.4%
> ~

I think that it is easy to understand exponential distribution when I check the exponential parameter. I also agree with it. So I create decile percents output
 in gaussian distribution.

Here are the examples.

> [nttcom@localhost postgresql]$ contrib/pgbench/pgbench --gaussian=20
> ~
> decile percents: 0.0% 0.0% 0.0% 0.0% 50.0% 50.0% 0.0% 0.0% 0.0% 0.0%
> ~
> [nttcom@localhost postgresql]$ contrib/pgbench/pgbench --gaussian=10
> ~
> decile percents: 0.0% 0.0% 0.0% 2.3% 47.7% 47.7% 2.3% 0.0% 0.0% 0.0%
> ~
> [nttcom@localhost postgresql]$ contrib/pgbench/pgbench --gaussian=5
> ~
> decile percents: 0.0% 0.1% 2.1% 13.6% 34.1% 34.1% 13.6% 2.1% 0.1% 0.0%

I think that it is easier than before. Sum of decile percents is just 100%.

However, I don't prefer "highest/lowest percentage" because it will be confused
 with decile percentage for users, and anyone cannot understand this digits. 

Here is example when sets exponential=5,
> [nttcom@localhost postgresql]$ contrib/pgbench/pgbench --exponential=5
> ~
> decile percents: 39.6% 24.0% 14.6% 8.8% 5.4% 3.3% 2.0% 1.2% 0.7% 0.4%
> highest/lowest percent of the range: 4.9% 0.0%
> ~

I cannot understand "4.9%, 0.0%" when I see the first time.

Then, I checked the source code, I understood it:( It's not good design...

#Why this parameter use 100?
So I'd like to remove it if you like. It will be more simple.

Attached patch is fixed version, please confirm it.

#Of course, World Cup is being held now. I'm not hurry at all.

Best regards,

--

Mitsumasa KONDO