Hello Fabien,

> I think that this method should be used for a>1, and the other very rough one 
> can be kept for parameter a in [0, 1), a case which does not make much sense 
> to a mathematician as it diverges if unbounded.

Now “a” does not have upper bound, that’s why on using iterative algorithm with 
a >= 10000 program will stuck on infinite loop because of following line of 
double b = pow(2.0, s - 1.0); 
Because after overflow “b” becomes “+Inf”.

So should upper bound for “a" be set? 

Should I mention in docs that there are two algorithms are used depending on 
values of a(s/theta)?

In attaching patch, I have added computeIterativeZipfian method and it’s usage 
in getZipfianRand.
Is it better to move code of computing via cache to new method, so that 
getZipfianRand will contain only 2 computeXXXZipfian method calls?

Attachment: pgbench-zipf-06v.patch
Description: Binary data

Thanks and Regards,
Alik Khilazhev
Postgres Professional:
The Russian Postgres Company

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