Performance

Install APCu Polyfill if your Server Uses APC

If your production server still uses the legacy APC PHP extension instead of OPcache, 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.

Enable APC Caching for the Autoloader

The class autoloading mechanism is one of the slowest parts in PHP applications that make use of lots of classes, such as Symfony. A simple way to improve its performance is to use the ApcClassLoader, which caches the location of each class after it's located the first time.

To use it, adapt your front controller file like this:

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// app.php
// ...

$loader = require_once __DIR__.'/../app/bootstrap.php.cache';

// Change 'sf' by something unique to this app to prevent
// conflicts with other applications running in the same server
$loader = new ApcClassLoader('sf', $loader);
$loader->register(true);

// ...

For more details, see Cache a Class Loader.

Use Bootstrap Files

The Symfony Standard Edition includes a script to generate a so-called bootstrap file, which is a large file containing the code of the most commonly used classes. This saves a lot of IO operations because Symfony no longer needs to look for and read those files.

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:

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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.

Use the OPcache Byte Code Cache

OPcache stores the compiled PHP files to avoid having to recompile them for every request. There are some byte code caches available, but as of PHP 5.5, PHP comes with OPcache built-in. For older versions, the most widely used byte code cache is APC.

Configure OPcache for Maximum Performance

The default OPcache configuration is not suited for Symfony applications, so it's recommended to change these settings as follows:

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; php.ini
; maximum memory that OPcache can use to store compiled PHP files
opcache.memory_consumption=256

; maximum number of files that can be stored in the cache
opcache.max_accelerated_files=20000

Don't Check PHP Files Timestamps

In production servers, PHP files should never change, unless a new application version is deployed. However, by default OPcache checks if cached files have changed their contents since they were cached. This check introduces some overhead that can be avoided as follows:

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; php.ini
opcache.validate_timestamps=0

After each deploy, you must empty and regenerate the cache of OPcache. Otherwise you won't see the updates made in the application. Given than in PHP, the CLI and the web processes don't share the same OPcache, you cannot clear the web server OPcache by executing some command in your terminal. These are some of the possible solutions:

1. Restart the web server;
2. 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);
3. Use the cachetool utility to control APC and OPcache from the CLI.

Configure the PHP realpath Cache

When a relative path is transformed into its real and absolute path, PHP caches the result to improve performance. Applications that open many PHP files, such as Symfony projects, should use at least these values:

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; php.ini
; maximum memory allocated to store the results
realpath_cache_size=4096K

; save the results for 10 minutes (600 seconds)
realpath_cache_ttl=600

Optimize Composer Autoloader

The class loader used while developing the application is optimized to find new and changed classes. In production servers, PHP files should never change, unless a new application version is deployed. That's why you can optimize Composer's autoloader to scan the entire application once and build a "class map", which is a big array of the locations of all the classes and it's stored in vendor/composer/autoload_classmap.php.

Execute this command to generate the class map (and make it part of your deployment process too):

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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.