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Symfony is fast, right out of the box. Of course, if you really need speed, there are many ways that you can make Symfony even faster. In this chapter, you'll explore many of the most common and powerful ways to make your Symfony application even faster.
One of the best (and easiest) things that you should do to improve your performance is to use a "byte code cache". The idea of a byte code cache is to remove the need to constantly recompile the PHP source code. There are a number of byte code caches available, some of which are open source. As of PHP 5.5, PHP comes with OPcache built-in. For older versions, the most widely used byte code cache is probably APC
Using a byte code cache really has no downside, and Symfony has been architected to perform really well in this type of environment.
Byte code caches usually monitor the source files for changes. This ensures that if the source of a file changes, the byte code is recompiled automatically. This is really convenient, but obviously adds overhead.
For this reason, some byte code caches offer an option to disable these checks. Obviously, when disabling these checks, it will be up to the server admin to ensure that the cache is cleared whenever any source files change. Otherwise, the updates you've made won't be seen.
For example, to disable these checks in APC, simply add
By default, the Symfony Standard Edition uses Composer's autoloader in the autoload.php file. This autoloader is easy to use, as it will automatically find any new classes that you've placed in the registered directories.
Unfortunately, this comes at a cost, as the loader iterates over all configured
namespaces to find a particular file, making
file_exists calls until it
finally finds the file it's looking for.
The simplest solution is to tell Composer to build a "class map" (i.e. a big array of the locations of all the classes). This can be done from the command line, and might become part of your deploy process:
$ composer dump-autoload --optimize
Internally, this builds the big class map array in
Another solution is to cache the location of each class after it's located the first time. Symfony comes with a class - ApcClassLoader - that does exactly this. To use it, just adapt your front controller file. If you're using the Standard Distribution, this code should already be available as comments in this file:
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// app.php // ... $loader = require __DIR__.'/../app/autoload.php'; include_once __DIR__.'/../var/bootstrap.php.cache'; // Enable APC for autoloading to improve performance. // You should change the ApcClassLoader first argument to a unique prefix // in order to prevent cache key conflicts with other applications // also using APC. /* $apcLoader = new Symfony\Component\ClassLoader\ApcClassLoader(sha1(__FILE__), $loader); $loader->unregister(); $apcLoader->register(true); */ // ...
For more details, see Cache a Class Loader.
When using the APC autoloader, if you add new classes, they will be found automatically and everything will work the same as before (i.e. no reason to "clear" the cache). However, if you change the location of a particular namespace or prefix, you'll need to flush your APC cache. Otherwise, the autoloader will still be looking at the old location for all classes inside that namespace.
To ensure optimal flexibility and code reuse, Symfony applications leverage a variety of classes and 3rd party components. But loading all of these classes from separate files on each request can result in some overhead. To reduce this overhead, the Symfony Standard Edition provides a script to generate a so-called bootstrap file, consisting of multiple classes definitions in a single file. By including this file (which contains a copy of many of the core classes), Symfony no longer needs to include any of the source files containing those classes. This will reduce disc IO quite a bit.
If you're using the Symfony Standard Edition, then you're probably already
using the bootstrap file. To be sure, open your front controller (usually
app.php) and check to make sure that the following line exists:
Note that there are two disadvantages when using a bootstrap file:
- the file needs to be regenerated whenever any of the original sources change (i.e. when you update the Symfony source or vendor libraries);
- when debugging, one will need to place break points inside the bootstrap file.
If you're using the Symfony Standard Edition, the bootstrap file is automatically
rebuilt after updating the vendor libraries via the
composer install command.
Even when using a byte code cache, performance will improve when using a bootstrap
file since there will be fewer files to monitor for changes. Of course if this
feature is disabled in the byte code cache (e.g.
apc.stat=0 in APC), there
is no longer a reason to use a bootstrap file.