[Kamailio-Users] Dispatcher hash algorithms.

[Daniel-Constantin Mierla]

Hello,

On 10/06/08 13:27, Henning Westerholt wrote:
> On Tuesday 30 September 2008, Daniel-Constantin Mierla wrote:
>   
>>> [..]
>>> Sure, it's great if my registrants always go to the same location
>>> server, but if 90% of my users end up going to one location server
>>> because of the distribution that the variance of their From URIs
>>> provides, what does this really give me except a predictable route?
>>> It's not as if I can use the hash to "find" a user's location server
>>> -- unless the location server was determined using the same hash also.
>>> What's the point?
>>>       
>> The hash function was tested to get pretty fair distribution for AoR,
>> most of the hashed values respect this format. If 90% of your users end
>> up to same server, then you may need to code a bit :-) and add an
>> alternative hash function to the module. For me the existing one seems
>> good so far.
>>
>> I do not need to know where a user call is going. Practically, they
>> could share the same db backend for auth, but the location and other
>> user profiles details may be in memory for speed purposes. In what I am
>> doing, all the servers in a group have same config, if i add a new one,
>> I get a new dispersion of the users across servers.
>>
>> Getting the distribution is quite simple, take the has function and make
>> a simple app that takes as parameter a string and outputs the hash
>> value. Knowing your subscriber base ids, you can estimate the results of
>> dispatching.
>>     
>
> Hi Alex,
>
> don't that much about the dispatcher internals, but i think it also uses the 
> CRC32 hash. In my tests with the carrierroute module that uses this too, 
> requests over a random callid/ from user are distributed equally with about 
> +/- 5% accuracy, which i think is ok. If you need to adjust the target host 
> distribution, take a look at the hash_id functionality (carrierroute config 
> file mode), here you can specify the exact destination. We use also the this 
> approach of pre-calculating the hash value that Daniel described.
>
>   
dispatcher is using an internal function, from hash_func.h. God to know 
you have tested with crc32, I might make it available as alternative 
hashing function for dispatcher.

Cheers,
Daniel


-- 
Daniel-Constantin Mierla
http://www.asipto.com