23. 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.
23.1. 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.
23.1.1. 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');
23.1.2. 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');
23.1.3. 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');
23.1.4. 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');
23.1.5. 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');
23.2. 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();
23.2.1. 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', $array);
23.2.2. Checking¶
Checking whether cached data exists is very simple: just use the
contains()
method. It accepts a single argument which is the ID
of the cache entry.
<?php
if ($cacheDriver->contains('cache_id')) {
echo 'cache exists';
} else {
echo 'cache does not exist';
}
23.2.3. 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');
23.2.4. 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.
23.2.4.1. By Cache ID¶
<?php
$cacheDriver->delete('my_array');
23.2.4.2. All¶
If you simply want to delete all cache entries you can do so with
the deleteAll()
method.
<?php
$deleted = $cacheDriver->deleteAll();
23.2.5. 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_');
23.3. 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.
23.3.1. 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());
23.3.2. 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');
23.3.3. 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.
23.4. 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.
23.5. 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.