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single: Performance; Byte code cache; OPcache; APC

Performance

Symfony is fast, right out of the box. However, you can make it faster if you optimize your servers and your applications as explained in the following performance checklists.

Symfony Application Checklist

  1. Install APCu Polyfill if your server uses APC <performance-install-apcu-polyfill>
  2. Enable APC Caching for the Autoloader <performance-autoloader-apc-cache>
  3. Use Bootstrap Files <performance-use-bootstrap-files>

Production Server Checklist

  1. Use the OPcache byte code cache <performance-use-opcache>
  2. Configure OPcache for maximum performance <performance-configure-opcache>
  3. Don't check PHP files timestamps <performance-dont-check-timestamps>
  4. Configure the PHP realpath Cache <performance-configure-realpath-cache>
  5. Optimize Composer Autoloader <performance-optimize-composer-autoloader>

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 Symfony\\Component\\ClassLoader\\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:

// 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 /components/class_loader/cache_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

Caution

Thanks to the optimizations introduced in PHP 7, bootstrap files are no longer necessary when running your Symfony applications with PHP 7 or a newer PHP version.

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:

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.

Note

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.

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:

; 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:

; 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 that 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:

; 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

Note

PHP disables the realpath cache when the open_basedir config option is enabled.

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):

$ 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.

Learn more

  • /http_cache/varnish
  • /http_cache/form_csrf_caching