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I have a code which add extra memcache instance at run time, but this makes my keys lost. I know there are several libraries available like consistent_hash, hash_ring but I am unable to use them in my code. I know there is ketama available but couldn't find python code sample for it.

class MemcacheClient(memcache.Client):
    """ A memcache subclass. It currently allows you to add a new host at run
    time. 

    Sadly, this truely messes with the our keys. I.E. Adding a host at runtime
    effectively wipes our cache all together...Wonder why?
    """

    def _get_server(self, key):
        """ Current implementation of Memcache client
        """
        return super(MemcacheClient, self)._get_server(key)

    def add_server(self, server):
        """ Adds a host at runtime to client
        """
        # Create a new host entry
        server = memcache._Host(
            server, self.debug, dead_retry=self.dead_retry,
            socket_timeout=self.socket_timeout,
            flush_on_reconnect=self.flush_on_reconnect
        )
        # Add this to our server choices 
        self.servers.append(server)
        # Update our buckets
        self.buckets.append(server)


def random_key(size):
    """ Generates a random key
    """
    return ''.join(random.choice(string.letters) for _ in range(size))


if __name__ == '__main__':
    # We have 7 running memcached servers
    servers = ['127.0.0.1:1121%d' % i for i in range(1,8)]
    # We have 100 keys to split across our servers
    keys = [random_key(10) for i in range(100)]
    # Init our subclass
    client = MemcacheClient(servers=servers)
    # Distribute the keys on our servers
    for key in keys:
        client.set(key, 1)

    # Check how many keys come back 
    valid_keys = client.get_multi(keys)
    print '%s percent of keys matched' % ((len(valid_keys)/float(len(keys))) * 100)

    # We add another server...and pow!
    client.add_server('127.0.0.1:11218')
    print 'Added new server' 

    valid_keys = client.get_multi(keys)
    print '%s percent of keys stil matched' % ((len(valid_keys)/float(len(keys))) * 100)
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Last Post by Prithiv_1
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This worked for me. Any other suggestions?

def add_server(self, server=None):
        """ Adds a host at runtime to client
        """
        # Create a new host entry
        if server is None:

            server = memcache._Host(
                server, self.debug, dead_retry=self.dead_retry,
                socket_timeout=self.socket_timeout,
            #flush_on_reconnect=self.flush_on_reconnect
            )
        # Add this to our server choices
            self.servers.append(server)
        # Update our buckets
            self.buckets.append(server)
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