[Kamailio-Users] What happens with filled htables?

[Alex Balashov]

Daniel-Constantin Mierla wrote:

> just to be sure everyone got it right regarding the size attribute in 
> htable parameter ... the number of slots for hash table is 2^size (2 
> power size). So, size=4 means that the hash table has 16 slots.
> 
> Reason for that is the speed in getting the slot number - modulo 
> function is very fast in such cases, the slot number being actually a 
> bitwise operation: hash_value & (2^size - 1)
> --- 2^size is cached at startup.

Thanks, that was a much-needed clarification omitted from my explanation.

I have always been told that table sizes that are prime numbers result 
in better distribution of factors due to the way modulo works, although 
I am not a mathematician and don't have a ready understanding of why. 
Is this true?  Is there some reason you did not take this approach?  Is 
hash_value & 2(^size - 1) equally fast?

-- 
Alex Balashov - Principal
Evariste Systems
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