作业

<?php
class ConsistencyHash
{
    public $real_nodes = [
        'node1' => '127.0.0.1:6379',
        'node2' => '127.0.0.1:6380',
        'node3' => '127.0.0.1:6381',
        'node4' => '127.0.0.1:6382',
        'node5' => '127.0.0.1:6383',
        'node6' => '127.0.0.1:6384',
        'node7' => '127.0.0.1:6385',
        'node8' => '127.0.0.1:6386',
        'node9' => '127.0.0.1:6387',
        'node10' => '127.0.0.1:6388',
    ];
    public $nodes_key_num = [
        'node1' => 0,
        'node2' => 0,
        'node3' => 0,
        'node4' => 0,
        'node5' => 0,
        'node6' => 0,
        'node7' => 0,
        'node8' => 0,
        'node9' => 0,
        'node10' => 0
    ];
    public $virtual_nodes = [];
    public $virtual_num = 100;
    public function hash($node)
    {
        return sprintf('%u', crc32($node));
    }
    public function createNodes()
    {
        foreach ($this->real_nodes as $key => $node) {
            for ($i = 1; $i <= $this->virtual_num; $i++) {
                $v_k = 'virtual_' . $key . '_' . $i;
                $pos = $this->hash($v_k);
                $this->virtual_nodes[$pos] = $key;
            }
        }
        ksort($this->virtual_nodes);
        return $this;
    }
    public function getNode($key)
    {
        $pos = $this->hash($key);
        $node = '';
        foreach ($this->virtual_nodes as $key => $val) {
            if ($pos <= $key) {
                $node = $val;
                break;
            }
        }
        return $node;
    }
    public function setCache()
    {
        for ($i = 1; $i <= 1000000; $i++) {
            $key = 'test_' . $i;
            $node = $this->getNode($key);
            $node and $this->nodes_key_num[$node]++;
        }
        return $this;
    }
    public function getStd()
    {
        $len = count($this->nodes_key_num);
        $sum = array_sum($this->nodes_key_num);
        $avg = $sum / $len;
        $arr = array_values($this->nodes_key_num);
        $std = 0;
        for ($i = 0; $i < $len; $i++) {
            $std += ($arr[$i] - $avg) * ($arr[$i] - $avg);
        }
        return sqrt($std / $len);
    }
}
$std = (new ConsistencyHash())->createNodes()->setCache()->getStd();
echo '标准差为:'.$std;