Re: [HACKERS] [WIP] Zipfian distribution in pgbench

> Algorithm works with theta less than 1. The only problem here is that 
> theta can not be 1, because of next line of code
>
> cell->alpha = 1. / (1 - theta);
>
> That’s why I put such restriction. Now I see 2 possible solutions for that:
> 1) Exclude 1, and allow everything in range (0;+∞).

Yep.

> 2) Or just increase/decrease theta by very small number if it is 1.

Nope, this seems quite arbitrary.

> I've executed scripts that you attached with different theta and number 
> of outcomes(not n, n remains the same = 100) and I found out that for 
> theta = 0.1 and big number of outcomes it gives distribution very 
> similar to zipfian(for number of outcomes = 100 000, bias -6% to 8% in 
> whole range and for NOO = 1000 000, bias is -2% to 2%).

Ok, so you did not get the large bias for i=3. Strange.

> By, number of outcomes(NOO) I mean how many times random_zipfian was 
> called. For example: pgbench -f compte_bench.sql -t 100000 So, I think 
> it works but works worse for small number of outcomes. And also we need 
> to find optimal theta for better results.

Hmmm. I've run one million outcomes each time.

I'll check on the next version.

-- 
Fabien.