#66 distribute the read operation on Redis Cache

Cache.php

@@ -53,6 +53,27 @@
  * ]
  * ~~~
  *
+ * If you ever need to make the cache read from Replica.
+ * e.g. AWS ElasticCache Redis, default all read go to master node
+ *
+ * ~~~
+ * [
+ *     'components' => [
+ *         'cache' => [
+ *             'class' => 'yii\redis\Cache',
+ *             'enableReplicas' => true,
+ *             'replicas' => [
+ *                 //replica redis connection, (default class will be yii\redis\Connection if not provided)
+ *                 //you can optionally put in master as hostname as well, as all GET operation will use replicas
+ *                 ['hostname' => 'redis-master.xyz.ng.0001.apse1.cache.amazonaws.com'],
+ *                 ['hostname' => 'redis-slave-002.xyz.0001.apse1.cache.amazonaws.com'],
+ *                 ['hostname' => 'redis-slave-003.xyz.0001.apse1.cache.amazonaws.com'],
+ *             ],
+ *         ],
+ *     ],
+ * ]
+ * ~~~
+ *
  * @author Carsten Brandt <mail@cebe.cc>
  * @since 2.0
  */
@@ -67,6 +88,21 @@ class Cache extends \yii\caching\Cache
      */
     public $redis = 'redis';
 
+    /**
+     * @var bool
+     */
+    public $enableReplicas = false;
+
+    /**
+     * @var array
+     */
+    public $replicas = [];
+
+    /**
+     * @var Connection
+     */
+    private $_replica;
+
 
     /**
      * Initializes the redis Cache component.
@@ -99,15 +135,15 @@ public function exists($key)
      */
     protected function getValue($key)
     {
-        return $this->redis->executeCommand('GET', [$key]);
+        return $this->getReplica()->executeCommand('GET', [$key]);
     }
 
     /**
      * @inheritdoc
      */
     protected function getValues($keys)
     {
-        $response = $this->redis->executeCommand('MGET', $keys);
+        $response = $this->getReplica()->executeCommand('MGET', $keys);
         $result = [];
         $i = 0;
         foreach ($keys as $key) {
@@ -195,4 +231,47 @@ protected function flushValues()
     {
         return $this->redis->executeCommand('FLUSHDB');
     }
+
+    /**
+     * @inheritdoc
+     * @return Connection
+     */
+    protected function getReplica()
+    {
+        if ($this->enableReplicas === false) {
+            return $this->redis;
+        }
+
+        if (isset($this->_replica)) {
+            return $this->_replica;
+        }
+
+        if (empty($this->replicas)) {
+            return $this->_replica = $this->redis;
+        }
+
+        if (count($this->replicas) >= 2) {
+            shuffle($this->replicas);
+        }
+        $config = array_shift($this->replicas);
+        if (is_array($config)) {
+            if (!isset($config['class'])) {
+                $config['class'] = 'yii\redis\Connection';
+            }
+
+            //--- if hostname same, no need re-open connection
+            if (isset($config['hostname']) && $config['hostname'] === $this->redis->hostname) {
+                return $this->_replica = $this->redis;
+            }
+
+            /** @var Connection $redis */
+            $redis = Yii::createObject($config);
+            if ($redis instanceof Connection) {
+                return $this->_replica = $redis;
+            }
+        }
+
+        Yii::trace('Fall back to redis master');
+        return $this->_replica = $this->redis;
+    }
 }

tests/RedisCacheTest.php

@@ -39,6 +39,12 @@ protected function getCacheInstance()
         return $this->_cacheInstance;
     }
 
+    protected function resetCacheInstance()
+    {
+        $this->getCacheInstance()->flush();
+        $this->_cacheInstance = null;
+    }
+
     public function testExpireMilliseconds()
     {
         $cache = $this->getCacheInstance();
@@ -120,4 +126,73 @@ public function testMultiByteGetAndSet()
         $cache->set($key, $data);
         $this->assertSame($cache->get($key), $data);
     }
+
+    public function testReplica()
+    {
+        $this->resetCacheInstance();
+
+        $cache = $this->getCacheInstance();
+        $cache->enableReplicas = true;
+
+        $key = 'replica-1';
+        $value = 'replica';
+
+        //No Replica listed
+        $this->assertFalse($cache->get($key));
+        $cache->set($key, $value);
+        $this->assertSame($cache->get($key), $value);
+
+        $cache->replicas = [
+            ['hostname' => 'localhost'],
+        ];
+        $this->assertSame($cache->get($key), $value);
+
+        //One Replica listed
+        $this->resetCacheInstance();
+        $cache = $this->getCacheInstance();
+        $cache->enableReplicas = true;
+        $cache->replicas = [
+            ['hostname' => 'localhost'],
+        ];
+        $this->assertFalse($cache->get($key));
+        $cache->set($key, $value);
+        $this->assertSame($cache->get($key), $value);
+
+        //Multiple Replicas listed
+        $this->resetCacheInstance();
+        $cache = $this->getCacheInstance();
+        $cache->enableReplicas = true;
+
+        $cache->replicas = [
+            ['hostname' => '127.0.0.1'],
+            ['hostname' => '127.0.0.1'],
+        ];
+        $this->assertFalse($cache->get($key));
+        $cache->set($key, $value);
+        $this->assertSame($cache->get($key), $value);
+
+        //invalid config
+        $this->resetCacheInstance();
+        $cache = $this->getCacheInstance();
+        $cache->enableReplicas = true;
+
+        $cache->replicas = [
+            ['class' => 'yii\db\Connection'],
+        ];
+        $this->assertFalse($cache->get($key));
+        $cache->set($key, $value);
+        $this->assertSame($cache->get($key), $value);
+
+        //invalid config
+        $this->resetCacheInstance();
+        $cache = $this->getCacheInstance();
+        $cache->enableReplicas = true;
+
+        $cache->replicas = ['redis'];
+        $this->assertFalse($cache->get($key));
+        $cache->set($key, $value);
+        $this->assertSame($cache->get($key), $value);
+
+        $this->resetCacheInstance();
+    }
 }