Memcached缓存作用
Memcached是一种高性能的分布式内存对象缓存系统，常用于加速动态Web应用程序。它的作用是将应用程序常用的数据缓存在内存中，避免重复的计算和数据库读写，从而提高网站的响应速度和性能。具体来说，Memcached缓存的作用包括：
- 减少数据库负载：将频繁读写的数据存储在内存中，减少对数据库的访问，降低数据库负载，提高性能和稳定性。
- 提高网站响应速度：由于Memcached是基于内存的缓存，存取数据的速度非常快，因此可以显著提高响应速度，减少用户等待时间。
- 提高应用程序性能：通过使用Memcached缓存，应用程序可以减少计算量和I/O操作，降低服务器负载，提高稳定性。
- 分布式缓存：Memcached可以部署在多台服务器上，构建分布式缓存系统，提高容量和可靠性，避免单点故障。
Memcached缓存可以大大提高Web应用程序的性能和稳定性，对于高并发访问的Web应用程序尤为重要。
教程
- 进入软件管理，选择你正在使用的PHP版本，安装memcached扩展，也可以顺便安装opcache。
-
在 Session 配置中，将存储模式选择为 memcached。
WordPress设置
- 新建一个 object-cache.php 文件放到网站目录 /wp-content 下。
- 把代码复制到object-cache.php 文件里：
<?php if( // (isset($_POST['action']) && $_POST['action'] == 'query-attachments') || (isset($_GET['debug']) && $_GET['debug'] == 'sql') ){ return; } if(!defined('WP_CACHE_KEY_SALT')) define('WP_CACHE_KEY_SALT', ''); if(class_exists('Memcached')){ function wp_cache_add($key, $data, $group='', $expire=0){ global $wp_object_cache; return $wp_object_cache->add($key, $data, $group, (int) $expire); } function wp_cache_cas($cas_token, $key, $data, $group='', $expire=0){ global $wp_object_cache; return $wp_object_cache->cas($cas_token, $key, $data, $group, (int) $expire); } function wp_cache_close(){ global $wp_object_cache; return $wp_object_cache->close(); } function wp_cache_decr($key, $offset=1, $group=''){ global $wp_object_cache; return $wp_object_cache->decr($key, $offset, $group); } function wp_cache_delete($key, $group=''){ global $wp_object_cache; return $wp_object_cache->delete($key, $group); } function wp_cache_flush(){ global $wp_object_cache; return $wp_object_cache->flush(); } function wp_cache_get($key, $group='', $force=false, &$found=null){ global $wp_object_cache; return $wp_object_cache->get($key, $group, $force, $found); } function wp_cache_get_multiple($keys, $group='', $force=false){ global $wp_object_cache; return $wp_object_cache->get_multiple($keys, $group, $force); } function wp_cache_get_with_cas($key, $group='', &$cas_token=null){ global $wp_object_cache; return $wp_object_cache->get_with_cas($key, $group, $cas_token); } function wp_cache_incr($key, $offset=1, $group=''){ global $wp_object_cache; return $wp_object_cache->incr($key, $offset, $group); } if(!isset($_GET['debug']) || $_GET['debug'] != 'sql'){ function wp_cache_init(){ $GLOBALS['wp_object_cache'] = new WP_Object_Cache(); } } function wp_cache_replace($key, $data, $group='', $expire=0){ global $wp_object_cache; return $wp_object_cache->replace($key, $data, $group, (int) $expire); } // function wp_cache_set($key, $data, $group='', $expire=0){ // global $wp_object_cache; // if(defined('WP_INSTALLING') == false){ // return $wp_object_cache->set($key, $data, $group, $expire); // } else{ // return $wp_object_cache->delete($key, $group); // } // } function wp_cache_set($key, $data, $group='', $expire=0){ global $wp_object_cache; return $wp_object_cache->set($key, $data, $group, (int) $expire); } function wp_cache_switch_to_blog($blog_id){ global $wp_object_cache; return $wp_object_cache->switch_to_blog($blog_id); } function wp_cache_add_global_groups($groups){ global $wp_object_cache; $wp_object_cache->add_global_groups($groups); } function wp_cache_add_non_persistent_groups($groups){ global $wp_object_cache; $wp_object_cache->add_non_persistent_groups($groups); } function wp_cache_get_stats(){ global $wp_object_cache; return $wp_object_cache->get_stats(); } class WP_Object_Cache{ private $cache = []; private $mc = null; public $cache_hits = 0; public $cache_misses = 0; private $blog_prefix; private $global_prefix; protected $global_groups = []; protected $non_persistent_groups = []; public function add($id, $data, $group='default', $expire=0){ if(wp_suspend_cache_addition()){ return false; } $key=$this->build_key($id, $group); if($this->is_non_persistent_group($group)){ if($this->internal_cache_exists($key)){ return false; }else{ $this->add_to_internal_cache($key, $data); return true; } }else{ $result = $this->mc->add($key, $data, $expire); if($this->mc->getResultCode() === Memcached::RES_SUCCESS){ $this->add_to_internal_cache($key, $data); } else{ $this->delete_from_internal_cache($key); } return $result; } } public function replace($id, $data, $group='default', $expire=0){ $key = $this->build_key($id, $group); if($this->is_non_persistent_group($group)){ if(!$this->internal_cache_exists($key)){ return false; }else{ $this->add_to_internal_cache($key, $data); return true; } }else{ $result=$this->mc->replace($key, $data, $expire); if($this->mc->getResultCode() === Memcached::RES_SUCCESS){ $this->add_to_internal_cache($key, $data); } else{ $this->delete_from_internal_cache($key); } return $result; } } public function set($id, $data, $group='default', $expire=0){ $key=$this->build_key($id, $group); if($this->is_non_persistent_group($group)){ $this->add_to_internal_cache($key, $data); return true; }else{ $result = $this->mc->set($key, $data, $expire); if($this->mc->getResultCode() === Memcached::RES_SUCCESS){ $this->add_to_internal_cache($key, $data); } else{ $this->delete_from_internal_cache($key); } return $result; } } public function incr($id, $offset=1, $group='default'){ $key = $this->build_key($id, $group); $result = $this->mc->increment($key, $offset); if($this->mc->getResultCode() === Memcached::RES_SUCCESS){ $this->add_to_internal_cache($key, $result); } else{ $this->delete_from_internal_cache($key); } return $result; } public function decr($id, $offset=1, $group='default'){ $key = $this->build_key($id, $group); $result = $this->mc->decrement($key, $offset); if($this->mc->getResultCode() === Memcached::RES_SUCCESS){ $this->add_to_internal_cache($key, $result); } else{ $this->delete_from_internal_cache($key); } return $result; } public function delete($id, $group='default'){ $key=$this->build_key($id, $group); $this->delete_from_internal_cache($key); if($this->is_non_persistent_group($group)){ return true; } return $this->mc->delete($key); } public function flush(){ $this->cache = []; return $this->mc->flush(); } public function get($id, $group='default', $force=false, &$found=null){ $key = $this->build_key($id, $group); if($this->internal_cache_exists($key) && !$force){ $found = true; return $this->get_from_internal_cache($key); }elseif($this->is_non_persistent_group($group)){ $found = false; return false; } $value = $this->mc->get($key); if($this->mc->getResultCode() == Memcached::RES_NOTFOUND){ $found = false; return false; } else{ $found = true; $this->add_to_internal_cache($key, $value); return $value; } } public function get_multiple($ids, $group='default', $force=false){ $caches = []; $keys = []; foreach($ids as $id){ $keys[$id] = $this->build_key($id, $group); } if($this->is_non_persistent_group($group)){ foreach($keys as $id=>$key){ $caches[$id] = $this->get_from_internal_cache($key); } return $caches; } if(!$force){ foreach($keys as $id=>$key){ if($this->internal_cache_exists($key)){ $caches[$id] = $this->get_from_internal_cache($key); }else{ $force = true; break; } } if(!$force){ return $caches; } } $results = $this->mc->getMulti(array_values($keys)); foreach($keys as $id=>$key){ if($results && isset($results[$key])){ $caches[$id] = $results[$key]; $this->add_to_internal_cache($key, $caches[$id]); }else{ $caches[$id] = false; $this->delete_from_internal_cache($key); } } return $caches; } public function get_with_cas($id, $group='default', &$cas_token=null){ $key = $this->build_key($id, $group); if(defined('Memcached::GET_EXTENDED')){ $result = $this->mc->get($key, null, Memcached::GET_EXTENDED); if($this->mc->getResultCode() == Memcached::RES_NOTFOUND){ return false; }else{ $cas_token = $result['cas']; return $result['value']; } }else{ $result = $this->mc->get($key, null, $cas_token); if($this->mc->getResultCode() == Memcached::RES_NOTFOUND){ return false; }else{ return $result; } } } public function cas($cas_token, $id, $data, $group='default', $expire=0){ $key=$this->build_key($id, $group); if(is_object($data)){ $data=clone $data; } $this->delete_from_internal_cache($key); return $this->mc->cas($cas_token, $key, $data, $expire); } public function add_global_groups($groups){ $groups = (array) $groups; $groups = array_fill_keys($groups, true); $this->global_groups = array_merge($this->global_groups, $groups); } public function add_non_persistent_groups($groups){ $groups=(array) $groups; $groups = array_fill_keys($groups, true); $this->non_persistent_groups = array_merge($this->non_persistent_groups, $groups); } public function switch_to_blog($blog_id){ if(is_multisite()){ $blog_id = intval($blog_id); $this->blog_prefix = $blog_id . ':'; }else{ global $table_prefix; $this->blog_prefix = $table_prefix . ':'; } } private function internal_cache_exists($key){ return $this->cache && isset($this->cache[$key]) && $this->cache[$key] !== false; } private function get_from_internal_cache($key){ if(!$this->internal_cache_exists($key)){ return false; } if(is_object($this->cache[$key])){ return clone $this->cache[$key]; } return $this->cache[$key]; } private function add_to_internal_cache($key, $value){ if(is_object($value)){ $value = clone $value; } $this->cache[$key]=$value; } private function delete_from_internal_cache($key){ unset($this->cache[$key]); } private function is_non_persistent_group($group){ $group = $group ?: 'default'; return isset($this->non_persistent_groups[$group]); } private function build_key($id, $group='default'){ $group = $group ?: 'default'; $prefix = isset($this->global_groups[$group]) ? $this->global_prefix : $this->blog_prefix; return preg_replace('/\s+/', '', WP_CACHE_KEY_SALT . $prefix . $group . ':' . $id); } public function get_stats(){ return $this->mc->getStats(); } public function get_mc(){ return $this->mc; } public function failure_callback($host, $port){ } public function close(){ $this->mc->quit(); } public function __construct(){ $this->mc=new Memcached(); $this->mc ->setOption(Memcached::OPT_LIBKETAMA_COMPATIBLE, true); if(!$this->mc->getServerList()){ $this->mc->addServer('127.0.0.1', 11211, 100); } // global $memcached_servers; // if(isset($memcached_servers)){ // $buckets=$memcached_servers; // } else{ // $buckets=array('127.0.0.1'); // } // reset($buckets); // if(is_int(key($buckets))){ // $buckets=array('default' => $buckets); // } // foreach($buckets as $bucket => $servers){ // $this->mc[ $bucket ]=new Memcached($bucket); // $this->mc[ $bucket ] ->setOption(Memcached::OPT_LIBKETAMA_COMPATIBLE, true); // if(count($this->mc[ $bucket ]->getServerList())){ // continue; // } // $instances=array(); // foreach($servers as $server){ // @list($node, $port)=explode(':', $server.":"); // if(empty($port)){ // $port=ini_get('memcache.default_port'); // } // $port=intval($port); // if(! $port){ // $port=11211; // } // $instances[]=array($node, $port, 1); // } // $this->mc[ $bucket ]->addServers($instances); // } if(is_multisite()){ $this->blog_prefix = get_current_blog_id() . ':'; $this->global_prefix = ''; }else{ global $table_prefix; $this->blog_prefix = $table_prefix . ':'; if(defined('CUSTOM_USER_TABLE') && defined('CUSTOM_USER_META_TABLE')){ $this->global_prefix = ''; }else{ $this->global_prefix = $table_prefix . ':'; } } // $this->cache_hits =& $this->stats['get']; // $this->cache_misses =& $this->stats['add']; } } } - 编辑网站根目录的 wp-config.php 文件，在
define('WP_DEBUG', false);的下方添加以下代码：
define('WP_CACHE', true);
完成后，WordPress 的 Memcached 缓存功能就启用了。
Memcached缓存功能确认
在浏览器中按下 F12，打开开发者工具，在 Network 选项卡中点击页面请求，在 Response Headers 中查找 X-Cache: HIT 或 X-Cache: MISS，即可判断是否启用了缓存。
PHP查询数据库确认
在 /wp-content/themes/主题/footer.php 中添加以下代码（放在
内）：
<?php echo sprintf(__('查询 %s 次，','b2'),get_num_queries()); ?>
<?php echo sprintf(__('耗时 %s 秒','b2'),timer_stop(0,4)); ?>
刷新前端页面，在底部将看到“查询 11 次，耗时 0.4945 秒”之类的信息，说明缓存生效。
如果缓存未生效，可能会看到“查询 326 次，耗时 1.4945 秒”等信息。你可以把 wp-config.php 中的 true 改为 false 或删除 object-cache.php 文件，对比差异。
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