# Question to Cache::Memcached

**Brad Fitzpatrick
**
brad@danga.com

*Mon, 7 Jun 2004 12:09:18 -0700 (PDT)*

>* How does the module decide which backend to give it too (if no weight value is
*>* specified)?
*
It runs the key through a hashing function, then mods that number with the
number of buckets (number of servers * each's weight) and uses the result
as the bucket number.
So if you have two servers:
10.0.0.1 weight 1 -> 1 bucket (bucket 0)
10.0.0.2 weight 3 -> 3 buckets (bucket 1, 2, 3)
Total: 4 buckets
So now we have key "foobar". HashValue("foobar") = 238423432423434.
Taking the hash value, mod 4 (4 buckets)...
238423432423434 % 4 = 2 (bucket 2)
So it uses 10.0.0.2
>* Is there a restriction on how the keys may look?
*
No spaces or newlines.
>* My keys are similar to this (without quotes):
*>*
*>* "010/dating/profilansicht/profilAnsicht.xmlindex=page1userid=2170797"
*
That looks fine.
So the mystery is: what hash values is it calculating for your keys?
It'd be way too weird if they were all 0.