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Updated the main performance article to make it more actionable #9161

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Updated the main performance article to make it more actionable
javiereguiluz Jan 29, 2018
6d43df8
Added back a note about bootstrap files and PHP 7
javiereguiluz Jan 29, 2018
fe4f032
Better explain how to empty cache after each deploy
javiereguiluz Jan 29, 2018
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Added a missing reference
javiereguiluz Jan 29, 2018
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296 changes: 150 additions & 146 deletions performance.rst
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.. index::
single: Tests
single: Performance; Byte code cache; OPcache; APC

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.
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.

.. index::
single: Performance; Byte code cache
Symfony Application Checklist
-----------------------------

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

Production Server Checklist
---------------------------

Use a Byte Code Cache (e.g. OPcache)
------------------------------------
#. :ref:`Use the OPcache byte code cache <performance-use-opcache>`
#. :ref:`Configure OPcache for maximum performance <performance-configure-opcache>`
#. :ref:`Don't check PHP files timestamps <performance-dont-check-timestamps>`
#. :ref:`Configure the PHP realpath Cache <performance-configure-realpath-cache>`
#. :ref:`Optimize Composer Autoloader <performance-optimize-composer-autoloader>`

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.
.. _performance-install-apcu-polyfill:

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`_.
Install APCu Polyfill if your Server Uses APC
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. tip::
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.

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.
.. _performance-autoloader-apc-cache:

Using a byte code cache really has no downside, and Symfony has been designed
to perform really well in this type of environment.
Enable APC Caching for the Autoloader
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Monitoring Source File Changes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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 :class:`Symfony\\Component\\ClassLoader\\ApcClassLoader`,
which caches the location of each class after it's located the first time.

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

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.
// app.php
// ...

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

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).
// 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 :doc:`/components/class_loader/cache_class_loader`.

.. 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. These are some of the possible solutions:
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.

#. Restart the web server;
#. Call the :phpfunction:`apc_clear_cache` or :phpfunction:`opcache_reset`
functions via the web server (i.e. by having these in a script that
you execute over the web);
#. Use the `cachetool`_ utility to control APC and OPcache from the CLI.
.. _performance-use-bootstrap-files:

Optimizing all the Files Used by Symfony
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Use Bootstrap Files
~~~~~~~~~~~~~~~~~~~

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:
.. caution::

.. code-block:: ini
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.

; php.ini
opcache.max_accelerated_files = 20000
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.

Configure the PHP realpath Cache
--------------------------------
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::

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

Consider increasing the ``realpath_cache_size`` and ``realpath_cache_ttl``:
Note that there are two disadvantages when using a bootstrap file:

.. code-block:: ini
* the file needs to be regenerated whenever any of the original sources change
(i.e. when you update the Symfony source or vendor libraries);

; php.ini
; 4096k is the default value in PHP 7.2
realpath_cache_size=4096K
realpath_cache_ttl=600
* when debugging, one will need to place break points inside the bootstrap file.

.. index::
single: Performance; Autoloader
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::

Use Composer's Class Map Functionality
--------------------------------------
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.

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.
.. _performance-use-opcache:

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.
Use the OPcache Byte Code Cache
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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``.
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`_.

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

.. code-block:: bash
Configure OPcache for Maximum Performance
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

$ composer dump-autoload --optimize --no-dev --classmap-authoritative
The default OPcache configuration is not suited for Symfony applications, so
it's recommended to change these settings as follows:

``--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.
.. code-block:: ini

Caching the Autoloader with APC
-------------------------------
; php.ini
; maximum memory that OPcache can use to store compiled PHP files
opcache.memory_consumption=256M

Another solution is to cache the location of each class after it's located
the first time. Symfony comes with a class - :class:`Symfony\\Component\\ClassLoader\\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::
; maximum number of files that can be stored in the cache
opcache.max_accelerated_files=20000

// app.php
// ...
.. _performance-dont-check-timestamps:

$loader = require_once __DIR__.'/../app/bootstrap.php.cache';
Don't Check PHP Files Timestamps
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

// 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);
*/
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:

// ...
.. code-block:: ini

For more details, see :doc:`/components/class_loader/cache_class_loader`.
; php.ini
opcache.validate_timestamps=0

.. note::
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:

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.
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.

.. index::
single: Performance; Bootstrap files
.. _performance-configure-realpath-cache:

Use Bootstrap Files
-------------------
Configure the PHP realpath Cache
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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.
When a relative path is transformed into its real and absolute path, PHP
caches the result to improve performance. The default config of this cache
is not suited for applications that open many PHP files, such as Symfony.
It's recommended to change these settings as follows:

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::
.. code-block:: ini

require_once __DIR__.'/../app/bootstrap.php.cache';
; php.ini
; maximum memory allocated to store the results
realpath_cache_size=4096K

Note that there are two disadvantages when using a bootstrap file:
; save the results for 10 minutes (600 seconds)
realpath_cache_ttl=600

* the file needs to be regenerated whenever any of the original sources change
(i.e. when you update the Symfony source or vendor libraries);
.. _performance-optimize-composer-autoloader:

* when debugging, one will need to place break points inside the bootstrap file.
Optimize Composer Autoloader
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you're using the Symfony Standard Edition, the bootstrap file is automatically
rebuilt after updating the vendor libraries via the ``composer install`` command.
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):

Bootstrap Files and Byte Code Caches
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. code-block:: bash

$ composer dump-autoload --optimize --no-dev --classmap-authoritative

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.
* ``--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
----------
Expand All @@ -209,10 +214,9 @@ Learn more

.. _`byte code caches`: https://en.wikipedia.org/wiki/List_of_PHP_accelerators
.. _`OPcache`: http://php.net/manual/en/book.opcache.php
.. _`opcache.max_accelerated_files`: http://php.net/manual/en/opcache.configuration.php#ini.opcache.max-accelerated-files
.. _`bootstrap file`: https://github.com/sensiolabs/SensioDistributionBundle/blob/master/Composer/ScriptHandler.php
.. _`Composer's autoloader optimization`: https://getcomposer.org/doc/articles/autoloader-optimization.md
.. _`APC`: http://php.net/manual/en/book.apc.php
.. _`APCu Polyfill component`: https://github.com/symfony/polyfill-apcu
.. _`APCu PHP functions`: http://php.net/manual/en/ref.apcu.php
.. _`autoload.php`: https://github.com/symfony/symfony-standard/blob/master/app/autoload.php
.. _`bootstrap file`: https://github.com/sensiolabs/SensioDistributionBundle/blob/master/Composer/ScriptHandler.php
.. _`cachetool`: https://github.com/gordalina/cachetool