Use proper redundancy options to make a failover seamless

Author: Oliver Stark

composer.json

@@ -1,7 +1,7 @@
 {
   "name": "fortrabbit/yii-memcached",
   "description": "Memcached Session & Cache for Craft3 / Yii2 on fortrabbit",
-  "version": "1.0.0",
+  "version": "1.1.0",
   "type": "yii2-extension",
 
   "keywords": ["yii2", "craftcms", "caching", "cache", "memcached", "memcache", "session"],

src/Bootstrap.php

@@ -15,6 +15,8 @@
 class Bootstrap implements BootstrapInterface
 {
 
+    const TIMEOUT_IN_MILLISECONDS = 50;
+
     /**
      * Bootstrapper
      *
@@ -31,6 +33,7 @@ public function bootstrap($app)
                     'class'        => MemCache::class,
                     'persistentId' => getenv('MEMCACHE_PERSISTENT') ? 'cache' : null,
                     'servers'      => $this->getMemcachedServers(),
+                    'options'      => $this->getOptions(),
                     'useMemcached' => true
                 ]);
             } catch (InvalidConfigException $e) {
@@ -51,13 +54,46 @@ protected function getMemcachedServers(): array
             $servers[] = [
                 'host'          => getenv('MEMCACHE_HOST' . $num),
                 'port'          => getenv('MEMCACHE_PORT' . $num),
-                'retryInterval' => 2,
-                'status'        => true,
-                'timeout'       => 2,
                 'weight'        => 1,
             ];
         }
 
         return $servers;
     }
+
+    /**
+     * @return array
+     */
+    protected function getOptions(): array
+    {
+        if (!extension_loaded('memcached')) {
+            return [];
+        }
+
+        return [
+
+            // Assure that dead servers are properly removed and ...
+            \Memcached::OPT_REMOVE_FAILED_SERVERS => true,
+
+            // ... retried after a short while (here: 2 seconds)
+            \Memcached::OPT_RETRY_TIMEOUT         => 2,
+
+            // KETAMA must be enabled so that replication can be used
+            \Memcached::OPT_LIBKETAMA_COMPATIBLE  => true,
+
+            // Replicate the data, i.e. write it to both memcached servers
+            \Memcached::OPT_NUMBER_OF_REPLICAS    => 1,
+
+            // Those values assure that a dead (due to increased latency or
+            // really unresponsive) memcached server increased dropped fast
+            // and the other is used.
+            \Memcached::OPT_POLL_TIMEOUT          => self::TIMEOUT_IN_MILLISECONDS,           // milliseconds
+            \Memcached::OPT_SEND_TIMEOUT          => self::TIMEOUT_IN_MILLISECONDS * 1000,    // microseconds
+            \Memcached::OPT_RECV_TIMEOUT          => self::TIMEOUT_IN_MILLISECONDS * 1000,    // microseconds
+            \Memcached::OPT_CONNECT_TIMEOUT       => self::TIMEOUT_IN_MILLISECONDS,           // milliseconds
+
+            // Further performance tuning
+            \Memcached::OPT_NO_BLOCK              => true,
+        ];
+    }
 }

src/init.php

@@ -12,11 +12,13 @@
     // session config
     ini_set('session.save_handler', 'memcached');
     ini_set('session.save_path', implode(',', $handlers));
+    ini_set('memcached.sess_locking', 0);
 
     if (getenv('MEMCACHE_COUNT') == 2) {
         ini_set('memcached.sess_number_of_replicas', 1);
         ini_set('memcached.sess_consistent_hash', 1);
         ini_set('memcached.sess_binary', 1);
+        ini_set('memcached.sess_remove_failed_servers', 1);
     }
 }