我在PHP中的Memcached持久性有问题。Memcached lib 返回空getServerList()，直到有 10 个并发连接。找不到合理的解释，但找到了有同样问题的人（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单addServers运行。
全新运行（在 memcached/apache 重新启动后）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？发生了什么事情？
我的配置：
- 乌班图13.04
- 阿帕奇 2.2.22
- 内存缓存服务器 1.4.14（4 个实例）
- libmemcached 1.0.8
- PHP 5.4.9-4ubuntu2.3
- Memcached lib for PHP latest。
更新 2014.04.22
问题仍然存在于我的最新配置中：
- Xubuntu 13.10 （内核 3.11.0-19）
- 阿帕奇 2.4.6
- 内存 1.4.14
- libmemcached 1.0.8
- PHP 5.5.3-1ubuntu2.3
- Memcached lib for PHP 2.1.0
我不确定我是否看到您的"问题"是什么。你的每个Apache PHP"服务器"（即子工）在启动时还没有连接到memcache - 所以每个都需要初始化一个连接 - 他们每个人都需要...一次。
现在，每个工作线程都有一个服务器列表。
如果您要第二次查询它 - 您将"看到"服务器列表。但是您有一个缓存对象，我假设您只实例化一次。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......因此，您永远不会看到"这是服务器列表"。
我有正确吗？
如果是这样，这是关于"单例"的常见问题/误解之一。关于单身人士，你总是需要问的最重要的问题是"有多少人"——因为他们只是在他们控制的上下文中是"单身"的......但就像在这种情况下一样 - 其他外部因素可能会使它们更多。在这种情况下，每个 PHP 实例都有一个。但是您的 Apache 会创建多个 PHP 实例 - 所以每个实例都有一个 - 并且这些实例不共享任何内容，因此每个实例都需要自己的全局变量、与数据库的持久连接、与 memcache 的持久连接等。
很高兴得到纠正。
如果您使用的是php-fpm（或与Apache类似的配置），则每个php子级将创建自己的与memcache的持久连接。因此，如果 php-fpm 配置为创建 10 个子级，则您的日志输出完全有意义：-）