Memcached 之取模与哈希算法命中率实验

当5台memcache服务器中有一台宕机时的命中率实验。

一、php实现代码

　　1. config.php

        $server = array(
		"A" => array("host" => "127.0.0.1", "port" => 11211),
		"B" => array("host" => "127.0.0.1", "port" => 11212),
		"C" => array("host" => "127.0.0.1", "port" => 11213),
		"D" => array("host" => "127.0.0.1", "port" => 11214),
		"E" => array("host" => "127.0.0.1", "port" => 11215),
	);

	$_dis = "Moder";//Consistent

　　2. hash.php

interface hasher {public function _hash($str);}
	interface distribution {public function lookup($key);}

	/**
	* 	取模算法类
	*/
	class Moder implements hasher,distribution
	{
		
		protected $_nodes = array();
		protected $_cnt = 0;

		public function _hash($str) {
			return sprintf('%u',crc32($str)); // 把字符串转成 32 位符号整数
		}

		public function addNode($node){
			if (in_array($node, $this->_nodes)) {
				return true;
			}
			$this->_nodes[] = $node;
			$this->_cnt += 1;
			return true;
		}

		public function delNode($node) {
			if (!in_array($node, $this->_nodes)) {
				return true;
			}
			$key = array_search($node, $this->_nodes);
			unset($this->_nodes[$key]);
			$this->_cnt -= 1;
			return true;
		}

		public function lookup($key) {
			$key = $this->_hash($key) % $this->_cnt;
			return $this->_nodes[$key];
		}

		public  function printNodes()
		{
			print_r($this->_nodes);
		}
	}

	/*
	$mode = new Moder();
	$mode->addNode('a');
	$mode->addNode('b');
	$mode->addNode('c');

	$key = "sssa";

	$mode->printNodes();

	echo $mode->_hash($key)."<br/>";

	echo $mode->lookup($key);
	*/


	/**
	*	一致性hash算法类
	*/
	class Consistent implements hasher,distribution{
		protected $_nodes = array(); //服务器节点
		protected $_postion = array();//虚拟节点
		protected $_mul = 64; //每个节点对应 64 个虚节点
		public function _hash($str) {
			return sprintf('%u',crc32($str)); // 把字符串转成 32 位符号整数
		}
		// 核心功能
		public function lookup($key) {
			$point = $this->_hash($key);
			$node = current($this->_postion); //先取圆环上最小的一个节点,当成结果
			foreach($this->_postion as $k=>$v) {
				if($point <= $k) 
				{
					$node = $v;
					break;
				}
			}
			reset($this->_postion);
			return $node;
		}
		//添加节点
		public function addNode($node) {
			if(isset($this->nodes[$node])) {
				return;
			}
			for($i=0; $i<$this->_mul; $i++) {
				$pos = $this->_hash($node . '-' . $i);
				$this->_postion[$pos] = $node;
				$this->_nodes[$node][] = $pos;
			}
			$this->_sortPos();
		}
		// 循环所有的虚节点,谁的值==指定的真实节点 ,就把他删掉
		public function delNode($node) {
			if(!isset($this->_nodes[$node])) {
				return;
			}
			foreach($this->_nodes[$node] as $k) {
				unset($this->_postion[$k]);
			}
			unset($this->_nodes[$node]);
		}
		//将虚拟节点排序
		protected function _sortPos() {
			ksort($this->_postion,SORT_REGULAR);
		}
	}

	/*
	// 测试
	$con = new Consistent();
	$con->addNode('a');
	$con->addNode('b');
	$con->addNode('c');
	$key = 'www.zixue.it';
	echo '此 key 落在'.$con->lookup($key).'号节点';
	*/

　　3.initData.php（初始化数据）

        include './config.php';
	include './hash.php';
	set_time_limit(0);
	$mem = new Memcache();
	$diser = new $_dis(); 
	foreach ($server as $key => $value) {
		$diser->addNode($key);
	}
	for ($i=0; $i < 1000; $i++) { 
		//获取服务器
		$serv = $server[$diser->lookup("key" . $i)];
		$mem->connect($serv['host'], $serv['port'], 2);
		$mem->add("key".$i, "value".$i, 0, 0);
	}

	echo "full";

　　4.load.php （获取数据的概率）

        include './config.php';
	include './hash.php';
	set_time_limit(0);
	$mem = new Memcache();
	$diser = new $_dis(); 
	foreach ($server as $key => $value) {
		$diser->addNode($key);
	}
	for ($i=0; $i < 1000; $i++) { 
		//获取服务器
		$serv = $server[$diser->lookup("key" . $i)];
		$mem->connect($serv['host'], $serv['port'], 2);
		$mem->add("key".$i, "value".$i, 0, 0);
	}

	echo "full";

　　5.exec.php （执行）

        //模拟减少一台服务器
	include './config.php';
	include './hash.php';

	$mem = new Memcache();
	$diser = new $_dis(); 
	foreach ($server as $key => $value) {
		$diser->addNode($key);
	}

	//删除一台服务器
	$diser->delNode("D");


	for ($i=0; $i < 10000; $i++) { 
		//获取服务器
		$serv = $server[$diser->lookup("key" . $i)];
		if ($serv) {
			$mem->connect($serv['host'], $serv['port'], 2);
			if(!$mem->get("key" . $i)){
				$mem->add("key".$i, "value".$i, 0, 0);
			}
		}
		
		usleep(3000);
	}

二、取模算法命中率

　　如图：

　　　　1.初始状态：