diff --git a/framework/yii/caching/Cache.php b/framework/yii/caching/Cache.php
index 0460b8c..fc1027c 100644
--- a/framework/yii/caching/Cache.php
+++ b/framework/yii/caching/Cache.php
@@ -7,7 +7,9 @@
 
 namespace yii\caching;
 
+use Yii;
 use yii\base\Component;
+use yii\base\InvalidConfigException;
 use yii\helpers\StringHelper;
 
 /**
@@ -52,10 +54,12 @@ use yii\helpers\StringHelper;
 abstract class Cache extends Component implements \ArrayAccess
 {
 	/**
-	 * @var string a string prefixed to every cache key so that it is unique. Defaults to null, meaning using
-	 * the value of [[Application::id]] as the key prefix. You may set this property to be an empty string
+	 * @var string a string prefixed to every cache key so that it is unique. If not set,
+	 * it will use a prefix generated from [[Application::id]]. You may set this property to be an empty string
 	 * if you don't want to use key prefix. It is recommended that you explicitly set this property to some
 	 * static value if the cached data needs to be shared among multiple applications.
+	 *
+	 * To ensure interoperability, only use alphanumeric characters should be used.
 	 */
 	public $keyPrefix;
 	/**
@@ -78,18 +82,18 @@ abstract class Cache extends Component implements \ArrayAccess
 	{
 		parent::init();
 		if ($this->keyPrefix === null) {
-			$this->keyPrefix = \Yii::$app->id;
+			$this->keyPrefix = substr(md5(Yii::$app->id), 0, 5);
+		} elseif (!ctype_alnum($this->keyPrefix)) {
+			throw new InvalidConfigException(get_class($this) . '::keyPrefix should only contain alphanumeric characters.');
 		}
 	}
 
 	/**
 	 * Builds a normalized cache key from a given key.
 	 *
-	 * The generated key contains letters and digits only, and its length is no more than 32.
-	 * 
 	 * If the given key is a string containing alphanumeric characters only and no more than 32 characters,
-	 * then the key will be returned back without change. Otherwise, a normalized key
-	 * is generated by serializing the given key and applying MD5 hashing.
+	 * then the key will be returned back prefixed with [[keyPrefix]]. Otherwise, a normalized key
+	 * is generated by serializing the given key, applying MD5 hashing, and prefixing with [[keyPrefix]].
 	 * 
 	 * The following example builds a cache key using three parameters:
 	 *
@@ -97,8 +101,8 @@ abstract class Cache extends Component implements \ArrayAccess
 	 * $key = $cache->buildKey(array($className, $method, $id));
 	 * ~~~
 	 *
-	 * @param array|string $key the key to be normalized
-	 * @return string the generated cache key include $this->keyPrefix
+	 * @param mixed $key the key to be normalized
+	 * @return string the generated cache key
 	 */
 	public function buildKey($key)
 	{
diff --git a/framework/yii/db/Command.php b/framework/yii/db/Command.php
index 657ef8d..17accf4 100644
--- a/framework/yii/db/Command.php
+++ b/framework/yii/db/Command.php
@@ -391,12 +391,12 @@ class Command extends \yii\base\Component
 		}
 
 		if (isset($cache) && $cache instanceof Cache) {
-			$cacheKey = $cache->buildKey(array(
+			$cacheKey = array(
 				__CLASS__,
 				$db->dsn,
 				$db->username,
 				$rawSql,
-			));
+			);
 			if (($result = $cache->get($cacheKey)) !== false) {
 				Yii::trace('Query result served from cache', __METHOD__);
 				return $result;
diff --git a/framework/yii/db/Schema.php b/framework/yii/db/Schema.php
index 9538e4c..c961244 100644
--- a/framework/yii/db/Schema.php
+++ b/framework/yii/db/Schema.php
@@ -89,7 +89,7 @@ abstract class Schema extends \yii\base\Object
 			/** @var $cache Cache */
 			$cache = is_string($db->schemaCache) ? Yii::$app->getComponent($db->schemaCache) : $db->schemaCache;
 			if ($cache instanceof Cache) {
-				$key = $this->getCacheKey($cache, $name);
+				$key = $this->getCacheKey($name);
 				if ($refresh || ($table = $cache->get($key)) === false) {
 					$table = $this->loadTableSchema($realName);
 					if ($table !== null) {
@@ -104,18 +104,17 @@ abstract class Schema extends \yii\base\Object
 
 	/**
 	 * Returns the cache key for the specified table name.
-	 * @param Cache $cache the cache component
 	 * @param string $name the table name
-	 * @return string the cache key
+	 * @return mixed the cache key
 	 */
-	public function getCacheKey($cache, $name)
+	public function getCacheKey($name)
 	{
-		return $cache->buildKey(array(
+		return array(
 			__CLASS__,
 			$this->db->dsn,
 			$this->db->username,
 			$name,
-		));
+		);
 	}
 
 	/**
@@ -178,7 +177,7 @@ abstract class Schema extends \yii\base\Object
 		$cache = is_string($this->db->schemaCache) ? Yii::$app->getComponent($this->db->schemaCache) : $this->db->schemaCache;
 		if ($this->db->enableSchemaCache && $cache instanceof Cache) {
 			foreach ($this->_tables as $name => $table) {
-				$cache->delete($this->getCacheKey($cache, $name));
+				$cache->delete($this->getCacheKey($name));
 			}
 		}
 		$this->_tableNames = array();
diff --git a/framework/yii/web/CacheSession.php b/framework/yii/web/CacheSession.php
index c125f01..79acd74 100644
--- a/framework/yii/web/CacheSession.php
+++ b/framework/yii/web/CacheSession.php
@@ -97,10 +97,10 @@ class CacheSession extends Session
 	/**
 	 * Generates a unique key used for storing session data in cache.
 	 * @param string $id session variable name
-	 * @return string a safe cache key associated with the session variable name
+	 * @return mixed a safe cache key associated with the session variable name
 	 */
 	protected function calculateKey($id)
 	{
-		return $this->cache->buildKey(array(__CLASS__, $id));
+		return array(__CLASS__, $id);
 	}
 }
diff --git a/framework/yii/web/UrlManager.php b/framework/yii/web/UrlManager.php
index 5a3c391..47f5c5d 100644
--- a/framework/yii/web/UrlManager.php
+++ b/framework/yii/web/UrlManager.php
@@ -103,7 +103,7 @@ class UrlManager extends Component
 			$this->cache = Yii::$app->getComponent($this->cache);
 		}
 		if ($this->cache instanceof Cache) {
-			$key = $this->cache->buildKey(__CLASS__);
+			$key = __CLASS__;
 			$hash = md5(json_encode($this->rules));
 			if (($data = $this->cache->get($key)) !== false && isset($data[1]) && $data[1] === $hash) {
 				$this->rules = $data[0];
diff --git a/framework/yii/widgets/FragmentCache.php b/framework/yii/widgets/FragmentCache.php
index aa24acd..8445955 100644
--- a/framework/yii/widgets/FragmentCache.php
+++ b/framework/yii/widgets/FragmentCache.php
@@ -159,7 +159,7 @@ class FragmentCache extends Widget
 	/**
 	 * Generates a unique key used for storing the content in cache.
 	 * The key generated depends on both [[id]] and [[variations]].
-	 * @return string a valid cache key
+	 * @return mixed a valid cache key
 	 */
 	protected function calculateKey()
 	{
@@ -169,6 +169,6 @@ class FragmentCache extends Widget
 				$factors[] = $factor;
 			}
 		}
-		return $this->cache->buildKey($factors);
+		return $factors;
 	}
 }
diff --git a/tests/unit/framework/caching/CacheTestCase.php b/tests/unit/framework/caching/CacheTestCase.php
index 5808fa0..81ac5cc 100644
--- a/tests/unit/framework/caching/CacheTestCase.php
+++ b/tests/unit/framework/caching/CacheTestCase.php
@@ -65,7 +65,7 @@ abstract class CacheTestCase extends TestCase
 	{
 		$cache = $this->getCacheInstance();
 		$this->assertNotNull(\Yii::$app->id);
-		$this->assertEquals(\Yii::$app->id, $cache->keyPrefix);
+		$this->assertNotNull($cache->keyPrefix);
 	}
 
 	public function testSet()