RendezvousHashing.py

from Resizer import Resizer

class RendezvousHashing(Resizer):
    """Implement Highest Random Weight hashing method.

    Part of 'Functional Core' - methods of this class don't change
    any state or objects, all they do is take values and return values.
    """
    def __init__(self, nodes):
        pass

    def get_nodeid(self, key, nodes):
        """Find the node to use for the given key's storage."""
        hashes = []
        for node in nodes:
            hashes.append((hash(node.name+key), node))
        _, node = max(hashes)
        return node.id

    def add_node(self, node, nodes):
        """Nothing is done when a new node is added.

         If a new site Sn+1 is added, new object placements or requests will 
         compute n+1 hash values, and pick the largest of these. If an object 
         already in the system at Sk maps to this new site Sn+1, it will be 
         fetched afresh and cached at Sn+1. All clients will henceforth obtain
         it from this site, and the old cached copy at Sk will ultimately be 
         replaced by the local cache management algorithm."""
        return {}

    def get_storage(self, node):
        """Take all key-value pairs from this node.

        If Sk is taken offline, its objects will be remapped uniformly to the 
        remaining n-1 sites."""
        return node.hashmap