24. Caching

Doctrine provides cache drivers in the Common package for some of the most popular caching implementations such as APC, Memcache and Xcache. We also provide an ArrayCache driver which stores the data in a PHP array. Obviously, when using ArrayCache, the cache does not persist between requests, but this is useful for testing in a development environment.

24.1. Cache Drivers

The cache drivers follow a simple interface that is defined in Doctrine\Common\Cache\Cache. All the cache drivers extend a base class Doctrine\Common\Cache\AbstractCache which implements this interface.

The interface defines the following public methods for you to implement:

  • fetch($id) - Fetches an entry from the cache
  • contains($id) - Test if an entry exists in the cache
  • save($id, $data, $lifeTime = false) - Puts data into the cache
  • delete($id) - Deletes a cache entry

Each driver extends the AbstractCache class which defines a few abstract protected methods that each of the drivers must implement:

  • _doFetch($id)
  • _doContains($id)
  • _doSave($id, $data, $lifeTime = false)
  • _doDelete($id)

The public methods fetch(), contains() etc. use the above protected methods which are implemented by the drivers. The code is organized this way so that the protected methods in the drivers do the raw interaction with the cache implementation and the AbstractCache can build custom functionality on top of these methods.

24.1.1. 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. 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.

<?php
$cacheDriver = new \Doctrine\Common\Cache\ApcCache();
$cacheDriver->save('cache_id', 'my_data');

24.1.2. Memcache

In order to use the Memcache cache driver you must have it compiled and enabled in your php.ini. You can read about Memcache on the PHP website. 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 Memcache cache driver by itself.

<?php
$memcache = new Memcache();
$memcache->connect('memcache_host', 11211);

$cacheDriver = new \Doctrine\Common\Cache\MemcacheCache();
$cacheDriver->setMemcache($memcache);
$cacheDriver->save('cache_id', 'my_data');

24.1.3. Memcached

Memcached is a more recent and complete alternative extension to Memcache.

In order to use the Memcached cache driver you must have it compiled and enabled in your php.ini. You can read about Memcached on the PHP website. 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 Memcached cache driver by itself.

<?php
$memcached = new Memcached();
$memcached->addServer('memcache_host', 11211);

$cacheDriver = new \Doctrine\Common\Cache\MemcachedCache();
$cacheDriver->setMemcached($memcached);
$cacheDriver->save('cache_id', 'my_data');

24.1.4. 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. 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.

<?php
$cacheDriver = new \Doctrine\Common\Cache\XcacheCache();
$cacheDriver->save('cache_id', 'my_data');

24.1.5. Redis

In order to use the Redis cache driver you must have it compiled and enabled in your php.ini. You can read about what Redis is from here. Also check A PHP extension for Redis for how you can use and install the Redis PHP extension.

Below is a simple example of how you could use the Redis cache driver by itself.

<?php
$redis = new Redis();
$redis->connect('redis_host', 6379);

$cacheDriver = new \Doctrine\Common\Cache\RedisCache();
$cacheDriver->setRedis($redis);
$cacheDriver->save('cache_id', 'my_data');

24.2. Using Cache Drivers

In this section we’ll describe how you can fully utilize the API of the cache drivers to save data to a cache, check if some cached data exists, fetch the cached data and delete the cached data. We’ll use the ArrayCache implementation as our example here.

<?php
$cacheDriver = new \Doctrine\Common\Cache\ArrayCache();

24.2.1. Saving

Saving some data to the cache driver is as simple as using the save() method.

<?php
$cacheDriver->save('cache_id', 'my_data');

The save() method accepts three arguments which are described below:

  • $id - The cache id
  • $data - The cache entry/data.
  • $lifeTime - The lifetime. If != false, sets a specific lifetime for this cache entry (null => infinite lifeTime).

You can save any type of data whether it be a string, array, object, etc.

<?php
$array = array(
    'key1' => 'value1',
    'key2' => 'value2'
);
$cacheDriver->save('my_array', $array);

24.2.2. Checking

Checking whether cached data exists is very simple: just use the contains() method. It accepts a single argument which is the ID of the cache entry.

<?php
if ($cacheDriver->contains('cache_id')) {
    echo 'cache exists';
} else {
    echo 'cache does not exist';
}

24.2.3. Fetching

Now if you want to retrieve some cache entry you can use the fetch() method. It also accepts a single argument just like contains() which is again the ID of the cache entry.

<?php
$array = $cacheDriver->fetch('my_array');

24.2.4. Deleting

As you might guess, deleting is just as easy as saving, checking and fetching. You can delete by an individual ID, or you can delete all entries.

24.2.4.1. By Cache ID

<?php
$cacheDriver->delete('my_array');

24.2.4.2. All

If you simply want to delete all cache entries you can do so with the deleteAll() method.

<?php
$deleted = $cacheDriver->deleteAll();

24.2.5. Namespaces

If you heavily use caching in your application and use it in multiple parts of your application, or use it in different applications on the same server you may have issues with cache naming collisions. This can be worked around by using namespaces. You can set the namespace a cache driver should use by using the setNamespace() method.

<?php
$cacheDriver->setNamespace('my_namespace_');

24.3. Integrating with the ORM

The Doctrine ORM package is tightly integrated with the cache drivers to allow you to improve the performance of various aspects of Doctrine by simply making some additional configurations and method calls.

24.3.1. Query Cache

It is highly recommended that in a production environment you cache the transformation of a DQL query to its SQL counterpart. It doesn’t make sense to do this parsing multiple times as it doesn’t change unless you alter the DQL query.

This can be done by configuring the query cache implementation to use on your ORM configuration.

<?php
$config = new \Doctrine\ORM\Configuration();
$config->setQueryCacheImpl(new \Doctrine\Common\Cache\ApcCache());

24.3.2. Result Cache

The result cache can be used to cache the results of your queries so that we don’t have to query the database or hydrate the data again after the first time. You just need to configure the result cache implementation.

<?php
$config->setResultCacheImpl(new \Doctrine\Common\Cache\ApcCache());

Now when you’re executing DQL queries you can configure them to use the result cache.

<?php
$query = $em->createQuery('select u from \Entities\User u');
$query->useResultCache(true);

You can also configure an individual query to use a different result cache driver.

<?php
$query->setResultCacheDriver(new \Doctrine\Common\Cache\ApcCache());

Note

Setting the result cache driver on the query will automatically enable the result cache for the query. If you want to disable it pass false to useResultCache().

<?php
$query->useResultCache(false);

If you want to set the time the cache has to live you can use the setResultCacheLifetime() method.

<?php
$query->setResultCacheLifetime(3600);

The ID used to store the result set cache is a hash which is automatically generated for you if you don’t set a custom ID yourself with the setResultCacheId() method.

<?php
$query->setResultCacheId('my_custom_id');

You can also set the lifetime and cache ID by passing the values as the second and third argument to useResultCache().

<?php
$query->useResultCache(true, 3600, 'my_custom_id');

24.3.3. Metadata Cache

Your class metadata can be parsed from a few different sources like YAML, XML, Annotations, etc. Instead of parsing this information on each request we should cache it using one of the cache drivers.

Just like the query and result cache we need to configure it first.

<?php
$config->setMetadataCacheImpl(new \Doctrine\Common\Cache\ApcCache());

Now the metadata information will only be parsed once and stored in the cache driver.

24.4. Clearing the Cache

We’ve already shown you how you can use the API of the cache drivers to manually delete cache entries. For your convenience we offer a command line task to help you with clearing the query, result and metadata cache.

From the Doctrine command line you can run the following command.

$ ./doctrine clear-cache

Running this task with no arguments will clear all the cache for all the configured drivers. If you want to be more specific about what you clear you can use the following options.

To clear the query cache use the --query option.

$ ./doctrine clear-cache --query

To clear the metadata cache use the --metadata option.

$ ./doctrine clear-cache --metadata

To clear the result cache use the --result option.

$ ./doctrine clear-cache --result

When you use the --result option you can use some other options to be more specific about which queries’ result sets you want to clear.

Just like the API of the cache drivers you can clear based on an ID, regular expression, prefix or suffix.

$ ./doctrine clear-cache --result --id=cache_id

Or if you want to clear based on a regular expressions:

$ ./doctrine clear-cache --result --regex=users_.*

Or with a prefix:

$ ./doctrine clear-cache --result --prefix=users_

And finally with a suffix:

$ ./doctrine clear-cache --result --suffix=_my_account

Note

Using the --id, --regex, etc. options with the --query and --metadata are not allowed as it is not necessary to be specific about what you clear. You only ever need to completely clear the cache to remove stale entries.

24.5. Cache Slams

Something to be careful of when using the cache drivers is “cache slams”. Imagine you have a heavily trafficked website with some code that checks for the existence of a cache record and if it does not exist it generates the information and saves it to the cache. Now, if 100 requests were issued all at the same time and each one sees the cache does not exist and they all try to insert the same cache entry it could lock up APC, Xcache, etc. and cause problems. Ways exist to work around this, like pre-populating your cache and not letting your users’ requests populate the cache.

You can read more about cache slams in this blog post.

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