Retwis ported to modern Redis data types.

The example (and related documentation at redis.io) was not updated for
5 years. Redis had no sorted sets and hashes when the original code was
written (!). An update was really needed.

We also use a modern PHP client now: Predis. A copy is shipped within
this repository to make life easier to newcomers trying Redis for the
first time via this example.

Predis/Cluster/Distribution/DistributionStrategyInterface.php

@@ -0,0 +1,53 @@
+<?php
+
+/*
+ * This file is part of the Predis package.
+ *
+ * (c) Daniele Alessandri <suppakilla@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Predis\Cluster\Distribution;
+
+use Predis\Cluster\Hash\HashGeneratorInterface;
+
+/**
+ * A distributor implements the logic to automatically distribute
+ * keys among several nodes for client-side sharding.
+ *
+ * @author Daniele Alessandri <suppakilla@gmail.com>
+ */
+interface DistributionStrategyInterface
+{
+    /**
+     * Adds a node to the distributor with an optional weight.
+     *
+     * @param mixed $node   Node object.
+     * @param int   $weight Weight for the node.
+     */
+    public function add($node, $weight = null);
+
+    /**
+     * Removes a node from the distributor.
+     *
+     * @param mixed $node Node object.
+     */
+    public function remove($node);
+
+    /**
+     * Gets a node from the distributor using the computed hash of a key.
+     *
+     * @param  mixed $key
+     * @return mixed
+     */
+    public function get($key);
+
+    /**
+     * Returns the underlying hash generator instance.
+     *
+     * @return HashGeneratorInterface
+     */
+    public function getHashGenerator();
+}