php - PHP 中的持久内存缓存 - 服务器池不断增长，直到 curr_connections 10

Question

我在 PHP 中遇到 Memcached 持久性问题。 Memcached lib 返回空 getServerList() 直到有 10 个并发连接。找不到合理的解释，但发现有同样问题的人(没有解决方案)。

我的例子:

class Cache {

    protected $memcached;

    public function __construct($cache_name) {
        $instance_name = 'persistent-' . $cache_name;
        $this->memcached = new Memcached($instance_name);
        $server_count = count($this->memcached->getServerList());
        echo '[MC] Server count of ', $instance_name, ': ', $server_count, PHP_EOL;

        if (0 == $server_count) {
            $servers = array(array("localhost","16586"),array("localhost","16587"));
            echo '[MC] Adding servers: ', json_encode($servers), PHP_EOL;
            // options don't change anything in my case
            $this->memcached->setOptions(array(
                Memcached::OPT_DISTRIBUTION => Memcached::DISTRIBUTION_CONSISTENT,
                Memcached::OPT_LIBKETAMA_COMPATIBLE => true
            ));
            $this->memcached->addServers($servers);
        }

        $stats = $this->memcached->getStats();
        foreach($stats as $server => $data){
            echo '[MC] Stats of ', $server, ' curr_connections: ', $data['curr_connections'], ' total_connections: ', $data['total_connections'], PHP_EOL;
        }
    }

    public function get($key) {
        echo '[MC] Server for key: ', $key, ' is ', json_encode($this->memcached->getServerByKey($key)), PHP_EOL;
        $ret = $this->memcached->get($key);
        echo '[MC] Getting ', $key, ' with result: ', $ret, PHP_EOL;
        return $ret;
    }

    public function set($key, $data, $timeout = 0) {
        echo '[MC] Set of ', $key, ' with data: ', $data, PHP_EOL;
        return $this->memcached->set($key, $data, $timeout);
    }
}

$cache = new Cache('instance');

$ret = $cache->get('something');

if(empty($ret)) {
    $cache->set('something', true);
}

我对这段代码的期望是在建立连接后运行单个 addServers。

重新运行(在 memcached/apache 重启后)显示:

// first run
[MC] Server count of persistent-instance: 0
[MC] Adding servers: [["localhost","16586"],["localhost","16587"]]
[MC] Stats of localhost:16586 curr_connections: 5 total_connections: 6
[MC] Stats of localhost:16587 curr_connections: 5 total_connections: 6
[MC] Server for key: something is {"host":"localhost","port":16587,"weight":1}
[MC] Getting something with result: 
[MC] Set of something with data: 1

// second
[MC] Server count of persistent-instance: 0
[MC] Adding servers: [["localhost","16586"],["localhost","16587"]]
[MC] Stats of localhost:16586 curr_connections: 6 total_connections: 7
[MC] Stats of localhost:16587 curr_connections: 6 total_connections: 7
[MC] Server for key: something is {"host":"localhost","port":16587,"weight":1}
[MC] Getting something with result: 1

// up to 6th call curr_connections are growing and still adding servers to pool
[MC] Server count of persistent-instance: 0
[MC] Adding servers: [["localhost","16586"],["localhost","16587"]]
[MC] Stats of localhost:16586 curr_connections: 10 total_connections: 11
[MC] Stats of localhost:16587 curr_connections: 10 total_connections: 11
[MC] Server for key: something is {"host":"localhost","port":16587,"weight":1}
[MC] Getting something with result: 1

// 7th+ call finally with expected result
[MC] Server count of persistent-instance: 2
[MC] Stats of localhost:16586 curr_connections: 10 total_connections: 11
[MC] Stats of localhost:16587 curr_connections: 10 total_connections: 11
[MC] Server for key: something is {"host":"localhost","port":16587,"weight":1}
[MC] Getting something with result: 1

我错过了什么吗？发生了什么事？

我的配置:

• Ubuntu 13.04
• Apache 2.2.22
• Memcached 服务器 1.4.14(4 个实例)
• libmemcached 1.0.8
• PHP 5.4.9-4ubuntu2.3
• PHP 的 Memcached 库 latest .

更新 2014.04.22

问题在我的最新配置上仍然存在:

• Xubuntu 13.10(内核 3.11.0-19)
• Apache 2.4.6
• 内存缓存 1.4.14
• libmemcached 1.0.8
• PHP 5.5.3-1ubuntu2.3
• PHP 2.1.0 的 Memcached 库

Answer 1

我不确定我是否明白您的“问题”是什么。 您的每个 Apache PHP“服务器”(即子 worker )在启动时尚未连接到内存缓存 - 因此每个都需要初始化一个连接 - 他们每个都......一次。

现在每个 worker 都有一个服务器列表。

如果你第二次查询它——你会“看到”服务器列表.. 但是你有一个缓存对象，我假设你只实例化一次。所以你永远不会第二次调用它，所以它永远不会尝试第二次调用 getServers ......所以你永远不会看到“这里是服务器列表”。

我说的对吗？

如果是这样，这是关于“单例”的常见问题/误解之一。关于单例，您总是需要问的最重要的问题是“他们中有多少人”——因为他们只是在他们控制的上下文中是“单例”的……但在这种情况下——其他外部因素可能会更多他们。 在这种情况下，每个 PHP 实例都有一个....但是您的 apache 生成多个 PHP 实例 - 所以每个实例都会有一个 - 而那些共享没有，所以每个都需要它自己的全局变量，它自己与数据库的持久连接，与内存缓存的持久连接等。

很高兴被纠正。