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

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),
acase 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
infiniteloop because of following line of code: 
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
computeXXXZipfianmethod calls? 
—
Thanks and Regards,
Alik Khilazhev
Postgres Professional:
http://www.postgrespro.com
The Russian Postgres Company


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