What is a good function to map an id to memcache in a pool of servers?

Something like:

host = getHost(id)
>>> 172.16.25.52

Ideally, the algorithm should minimize the number of cache misses whe开发者_JS百科n the pool of servers is expanded / contracted.

Are there any known algorithms out there that do this? Or libraries, potentially (I'm using Python).

Thank you.

The memcached library does this by default. So you can just read the code from the repository: http://bazaar.launchpad.net/~python-memcached-team/python-memcached/trunk/annotate/head%3A/memcache.py#L274

As for minimizing the cache misses with an expanding/contracting pool... a difficult thing to do. Either you're not dividing the servers correctly at first or it will be less optimal when expanding/contracting. If you would have a maximum of N servers than it might be easier though, since you can make a couple of assumptions.