predis/lib/Predis/Distribution/KetamaPureRing.php

<?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\Distribution;

/**
 * This class implements an hashring-based distributor that uses the same
 * algorithm of libketama to distribute keys in a cluster using client-side
 * sharding.
 *
 * @author Daniele Alessandri <suppakilla@gmail.com>
 * @author Lorenzo Castelli <lcastelli@gmail.com>
 */
class KetamaPureRing extends HashRing
{
    const DEFAULT_REPLICAS = 160;

    /**
     *
     */
    public function __construct()
    {
        parent::__construct($this::DEFAULT_REPLICAS);
    }

    /**
     * {@inheritdoc}
     */
    protected function addNodeToRing(&$ring, $node, $totalNodes, $replicas, $weightRatio)
    {
        $nodeObject = $node['object'];
        $nodeHash = $this->getNodeHash($nodeObject);
        $replicas = (int) floor($weightRatio * $totalNodes * ($replicas / 4));

        for ($i = 0; $i < $replicas; $i++) {
            $unpackedDigest = unpack('V4', md5("$nodeHash-$i", true));
            foreach ($unpackedDigest as $key) {
                $ring[$key] = $nodeObject;
            }
        }
    }

    /**
     * {@inheritdoc}
     */
    public function hash($value)
    {
        $hash = unpack('V', md5($value, true));
        return $hash[1];
    }

    /**
     * {@inheritdoc}
     */
    protected function wrapAroundStrategy($upper, $lower, $ringKeysCount)
    {
        // Binary search for the first item in _ringkeys with a value greater
        // or equal to the key. If no such item exists, return the first item.
        return $lower < $ringKeysCount ? $lower : 0;
    }
}