Prefer PhpFileCache for caching docs

Removes APC and XCache because they are deprecated.

Removes APCu because it is not as performant as PhpFileCache and cannot
be cleared using console tools.

docs/en/reference/caching.rst

@@ -45,40 +45,24 @@ This documentation does not cover every single cache driver included
 with Doctrine. For an up-to-date-list, see the
 `cache directory on GitHub <https://github.com/doctrine/cache/tree/master/lib/Doctrine/Common/Cache>`.
 
-APC
-~~~
-
-In order to use the APC cache driver you must have it compiled and
-enabled in your php.ini. You can read about APC
-`in the PHP Documentation <http://us2.php.net/apc>`_. It will give
-you a little background information about what it is and how you
-can use it as well as how to install it.
-
-Below is a simple example of how you could use the APC cache driver
-by itself.
-
-.. code-block:: php
-
-    <?php
-    $cacheDriver = new \Doctrine\Common\Cache\ApcCache();
-    $cacheDriver->save('cache_id', 'my_data');
+PhpFileCache
+~~~~~~~~~~~~
 
-APCu
-~~~~
+The preferred cache driver is ``PhpFileCache``. This driver serializes
+cache items and writes them to a file. This allows for opcode caching
+to be used and provides high performance in most scenarios.
 
-In order to use the APCu cache driver you must have it compiled and
-enabled in your php.ini. You can read about APCu
-`in the PHP Documentation <http://us2.php.net/apcu>`_. It will give
-you a little background information about what it is and how you
-can use it as well as how to install it.
+In order to use the ``PhpFileCache`` driver it must be able to write to
+a directory.
 
-Below is a simple example of how you could use the APCu cache driver
-by itself.
+Below is an example of how to use the ``PhpFileCache`` driver by itself.
 
 .. code-block:: php
 
     <?php
-    $cacheDriver = new \Doctrine\Common\Cache\ApcuCache();
+    $cacheDriver = new \Doctrine\Common\Cache\PhpFileCache(
+        '/path/to/writable/directory'
+    );
     $cacheDriver->save('cache_id', 'my_data');
 
 Memcache
@@ -128,24 +112,6 @@ driver by itself.
     $cacheDriver->setMemcached($memcached);
     $cacheDriver->save('cache_id', 'my_data');
 
-Xcache
-~~~~~~
-
-In order to use the Xcache cache driver you must have it compiled
-and enabled in your php.ini. You can read about Xcache
-`here <http://xcache.lighttpd.net/>`_. It will give you a little
-background information about what it is and how you can use it as
-well as how to install it.
-
-Below is a simple example of how you could use the Xcache cache
-driver by itself.
-
-.. code-block:: php
-
-    <?php
-    $cacheDriver = new \Doctrine\Common\Cache\XcacheCache();
-    $cacheDriver->save('cache_id', 'my_data');
-
 Redis
 ~~~~~
 
@@ -304,8 +270,11 @@ use on your ORM configuration.
 .. code-block:: php
 
     <?php
+    $cacheDriver = new \Doctrine\Common\Cache\PhpFileCacheCache(
+        '/path/to/writable/directory'
+    );
     $config = new \Doctrine\ORM\Configuration();
-    $config->setQueryCacheImpl(new \Doctrine\Common\Cache\ApcuCache());
+    $config->setQueryCacheImpl($cacheDriver);
 
 Result Cache
 ~~~~~~~~~~~~
@@ -318,7 +287,11 @@ cache implementation.
 .. code-block:: php
 
     <?php
-    $config->setResultCacheImpl(new \Doctrine\Common\Cache\ApcuCache());
+    $cacheDriver = new \Doctrine\Common\Cache\PhpFileCacheCache(
+        '/path/to/writable/directory'
+    );
+    $config = new \Doctrine\ORM\Configuration();
+    $config->setResultCacheImpl($cacheDriver);
 
 Now when you're executing DQL queries you can configure them to use
 the result cache.
@@ -335,7 +308,11 @@ result cache driver.
 .. code-block:: php
 
     <?php
-    $query->setResultCacheDriver(new \Doctrine\Common\Cache\ApcuCache());
+    $cacheDriver = new \Doctrine\Common\Cache\PhpFileCacheCache(
+        '/path/to/writable/directory'
+    );
+    $config = new \Doctrine\ORM\Configuration();
+    $query->setResultCacheDriver($cacheDriver);
 
 .. note::
 
@@ -387,7 +364,11 @@ first.
 .. code-block:: php
 
     <?php
-    $config->setMetadataCacheImpl(new \Doctrine\Common\Cache\ApcuCache());
+    $cacheDriver = new \Doctrine\Common\Cache\PhpFileCacheCache(
+        '/path/to/writable/directory'
+    );
+    $config = new \Doctrine\ORM\Configuration();
+    $config->setMetadataCacheImpl($cacheDriver);
 
 Now the metadata information will only be parsed once and stored in
 the cache driver.
@@ -423,6 +404,12 @@ To clear the result cache use the ``orm:clear-cache:result`` task.
 All these tasks accept a ``--flush`` option to flush the entire
 contents of the cache instead of invalidating the entries.
 
+.. note::
+
+    None of these tasks will work with APC, APCu, or XCache drivers
+    because the memory that the cache is stored in is only accessible
+    to the webserver.
+
 Cache Chaining
 --------------