Performance

Performance

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 article, you'll explore some of the ways to make your Symfony application even faster.

Use a Byte Code Cache (e.g. OPcache)

The first thing that you should do to improve your performance is to use a "byte code cache". These caches store the compiled PHP files to avoid having to recompile them for every request.

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 APC.

Tip

If your server still uses the legacy APC PHP extension, install the APCu Polyfill component in your application to enable compatibility with APCu PHP functions and unlock support for advanced Symfony features, such as the APCu Cache adapter.

Using a byte code cache really has no downside, and Symfony has been designed to perform really well in this type of environment.

Monitoring Source File Changes

Most byte code caches 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 it adds overhead.

For this reason, some byte code caches offer an option to disable these checks. For example, to disable these checks in APC, simply add apc.stat=0 to your php.ini configuration.

When disabling these checks, it will be up to the server administrators to ensure that the cache is cleared whenever any source files change. Otherwise, the updates you've made in the application won't be seen.

For the same reasons, the byte code cache must also be cleared when deploying the application (for example by calling apc_clear_cache() PHP function when using APC and opcache_reset() when using OPcache).

Note

In PHP, the CLI and the web processes don't share the same OPcache. This means that you cannot clear the web server OPcache by executing some command in your terminal. You either need to restart the web server or call the apc_clear_cache() or opcache_reset() functions via the web server (i.e. by having these in a script that you execute over the web).

Optimizing all the Files Used by Symfony

By default, PHP's OPcache saves up to 2,000 files in the byte code cache. This number is too low for the typical Symfony application, so you should set a higher limit with the opcache.max_accelerated_files configuration option:

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; php.ini
opcache.max_accelerated_files = 20000

Configure the PHP realpath Cache

PHP uses an internal cache to store the result of mapping file paths to their real and absolute file system paths. This increases the performance for applications like Symfony that open many PHP files, especially on Windows systems.

By default PHP sets a realpath_cache_size of 16K which is too low for Symfony. Consider updating this value at least to 4096K. In addition, cached paths are only stored for 120 seconds by default. Consider updating this value too using the realpath_cache_ttl option:

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; php.ini
realpath_cache_size=4096K
realpath_cache_ttl=600

Use Composer's Class Map Functionality

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 an optimized "class map", which is a big array of the locations of all the classes and it's stored in vendor/composer/autoload_classmap.php.

The class map can be generated from the command line, and might become part of your deploy process:

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$ composer dump-autoload --optimize --no-dev --classmap-authoritative
--optimize
Dumps every PSR-0 and PSR-4 compatible class used in your application.
--no-dev
Excludes the classes that are only needed in the development environment (e.g. tests).
--classmap-authoritative
Prevents Composer from scanning the file system for classes that are not found in the class map.

Caching the Autoloader with APC

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, make the following changes:

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// app.php
// ...

use Symfony\Component\ClassLoader\ApcClassLoader;

$loader = require __DIR__.'/../app/autoload.php';
include_once __DIR__.'/../app/bootstrap.php.cache';

// Use APC for autoloading to improve performance
// Change 'sf2' by the prefix you want in order
// to prevent key conflict with another application
$loader = new ApcClassLoader('sf2', $loader);
$loader->register(true);

// ...

For more details, see Cache a Class Loader.

Note

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.

Use Bootstrap Files

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:

require_once __DIR__.'/../app/bootstrap.php.cache';

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.

Bootstrap Files and Byte Code Caches

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.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.