#66 distribute the read operation on Redis Cache

CHANGELOG.md

@@ -4,7 +4,7 @@ Yii Framework 2 redis extension Change Log
 2.0.8 under development
 -----------------------
 
-- no changes in this release.
+- Enh #66: Cache component can be configured to read / get from replicas (ryusoft)
 
 
 2.0.7 December 11, 2017

Cache.php

@@ -53,6 +53,28 @@
  * ]
  * ~~~
  *
+ * If you have multiple redis replicas (e.g. AWS ElasticCache Redis) you can configure the cache to
+ * send read operations to the replicas. If no replicas are configured, all operations will be performed on the
+ * master connection configured via the [[redis]] property.
+ *
+ * ~~~
+ * [
+ *     'components' => [
+ *         'cache' => [
+ *             'class' => 'yii\redis\Cache',
+ *             'enableReplicas' => true,
+ *             'replicas' => [
+ *                 // config for replica redis connections, (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
  */
@@ -66,6 +88,36 @@ class Cache extends \yii\caching\Cache
      * with a Redis [[Connection]] object.
      */
     public $redis = 'redis';
+    /**
+     * @var bool whether to enable read / get from redis replicas.
+     * @since 2.0.8
+     * @see $replicas
+     */
+    public $enableReplicas = false;
+    /**
+     * @var array the Redis [[Connection]] configurations for redis replicas.
+     * Each entry is a class configuration, which will be used to instantiate a replica connection.
+     * The default class is [[Connection|yii\redis\Connection]]. You should at least provide a hostname.
+     * 
+     * Configuration example:
+     *
+     * ```php
+     * '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'],
+     * ],
+     * ```
+     *
+     * @since 2.0.8
+     * @see $enableReplicas
+     */
+    public $replicas = [];
+
+    /**
+     * @var Connection currently active connection.
+     */
+    private $_replica;
 
 
     /**
@@ -99,15 +151,15 @@ 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 +247,32 @@ protected function flushValues()
     {
         return $this->redis->executeCommand('FLUSHDB');
     }
+
+    /**
+     * It will return the current Replica Redis [[Connection]], and fall back to default [[redis]] [[Connection]]
+     * defined in this instance. Only used in getValue() and getValues().
+     * @since 2.0.8
+     * @return array|string|Connection
+     * @throws \yii\base\InvalidConfigException
+     */
+    protected function getReplica()
+    {
+        if ($this->enableReplicas === false) {
+            return $this->redis;
+        }
+
+        if ($this->_replica !== null) {
+            return $this->_replica;
+        }
+
+        if (empty($this->replicas)) {
+            return $this->_replica = $this->redis;
+        }
+
+        $replicas = $this->replicas;
+        shuffle($replicas);
+        $config = array_shift($replicas);
+        $this->_replica = Instance::ensure($config, Connection::className());
+        return $this->_replica;
+    }
 }

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();
+    }
 }