yii2/docs/guide/tutorial-performance-tuning.md

Performance Tuning

Note: This section is under development.

There are many factors affecting the performance of your Web application. Some are environmental, some are related with your code, while some others are related with Yii itself. In this section, we will enumerate most of these factors and explain how you can improve your application performance by adjusting these factors.

Optimizing your PHP Environment

A well configured PHP environment is very important. In order to get maximum performance,

• Use the latest stable PHP version. Major releases of PHP may bring significant performance improvements.
• Enable bytecode caching with Opcache (PHP 5.5 or later) or APC (PHP 5.4 or earlier). Bytecode caching avoids the time spent in parsing and including PHP scripts for every incoming request.

Disabling Debug Mode

When running an application in production, you should disable debug mode. Yii uses the value of a constant named YII_DEBUG to indicate whether debug mode should be enabled. When debug mode is enabled, Yii will take extra time to generate and record debugging information.

You may place the following line of code at the beginning of the entry script to disable debug mode:

defined('YII_DEBUG') or define('YII_DEBUG', false);

Info: The default value of YII_DEBUG is false. So if you are certain that you do not change its default value somewhere else in your application code, you may simply remove the above line to disable debug mode.

Using Caching Techniques

You can use various caching techniques to significantly improve the performance of your application. For example, if your application allows users to enter text in Markdown format, you may consider caching the parsed Markdown content to avoid parsing the same Markdown text repeatedly in every request. Please refer to the Caching section to learn about the caching support provided by Yii.

Enabling Schema Caching

Schema caching is a special caching feature that should be enabled whenever you are using Active Record. As you know, Active Record is intelligent enough to detect schema information (e.g. column names, column types, constraints) about a DB table without requiring you to manually describe them. Active Record obtains this information by executing extra SQL queries. By enabling schema caching, the retrieved schema information will be saved in the cache and reused in future requests.

To enable schema caching, configure a cache application component to store the schema information and set yii\db\Connection::enableSchemaCache to be true in the application configuration:

return [
    // ...
    'components' => [
        // ...
        'cache' => [
            'class' => 'yii\caching\FileCache',
        ],
        'db' => [
            'class' => 'yii\db\Connection',
            'dsn' => 'mysql:host=localhost;dbname=mydatabase',
            'username' => 'root',
            'password' => '',
            'enableSchemaCache' => true,

            // Duration of schema cache.
            'schemaCacheDuration' => 3600,

            // Name of the cache component used to store schema information
            'schemaCache' => 'cache',
        ],
    ],
];

Combining and Minimizing Assets

A complex Web page often includes many CSS and/or JavaScript asset files. To reduce the number of HTTP requests and the overall download size of these assets, you should consider combining them into one single file and compressing it. This may greatly improve the page loading time and reduce the server load. For more details, please refer to the Assets section.

Using better storage for sessions

By default PHP uses files to handle sessions. It is OK for development and small projects. But when it comes to handling concurrent requests, it's better to switch to another storage such as database. You can do so by configuring your application via config/web.php:

return [
    // ...
    'components' => [
        'session' => [
            'class' => 'yii\web\DbSession',

            // Set the following if you want to use DB component other than
            // default 'db'.
            // 'db' => 'mydb',

            // To override default session table, set the following
            // 'sessionTable' => 'my_session',
        ],
    ],
];

You can use CacheSession to store sessions using cache. Note that some cache storage such as memcached has no guarantee that session data will not be lost, and it would lead to unexpected logouts.

If you have Redis on your server, it's highly recommended as session storage.

Optimizing Databases

Execute DB queries and fetching data from databases is often the main performance bottleneck in a Web application. Although using data caching techniques may alleviate the performance hit, it does not fully solve the problem. When the database contains enormous amounts of data and the cached data is invalid, fetching the latest data could be prohibitively expensive without proper database and query design.

A general technique to improve the performance of DB queries is to create indices for table columns that need to be filtered by. For example, if you need to look for a user record by username, you should create an index on username. Note that while indexing can make SELECT queries much faster, it will slow down INSERT, UPDATE and DELETE queries.

For complex DB queries, it is recommended that you create database views to save the query parsing and preparation time.

Last but not least, use LIMIT in your SELECT queries. This avoids fetching an overwhelming amount of data from the database and exhausting the memory allocated to PHP.

Using Plain Arrays

Although Active Record is very convenient to use, it is not as efficient as using plain arrays when you need to retrieve a large amount of data from database. In this case, you may consider calling asArray() while using Active Record to query data so that the retrieved data is represented as arrays instead of bulky Active Record objects. For example,

class PostController extends Controller
{
    public function actionIndex()
    {
        $posts = Post::find()->limit(100)->asArray()->all();
        
        return $this->render('index', ['posts' => $posts]);
    }
}

In the above code, $posts will be populated as an array of table rows. Each row is a plain array. To access the title column of the i-th row, you may use the expression $posts[$i]['title'].

You may also use DAO to build queries and retrieve data in plain arrays.

Composer autoloader optimization

In order to improve overall performance you can execute composer dumpautoload -o to optimize Composer autoloader.

Processing data in offline mode

In order to respond to user requests faster you can process heavy parts of the request later if there's no need for immediate response.

There are two common ways to achieve it: cron job processing and specialized queues.

In the first case we need to save the data that we want to process later to a persistent storage such as a database. A console command that is run regularly via cron job queries the database and processes the data if there is any.

The above solution is OK for many cases but has one significant drawback. We aren't aware if there's data to be processed before we query the database, so we're either querying the database quite often or we have a slight delay between data creation and processing.

This issue could be solved by using a queue and job servers such RabbitMQ, ActiveMQ, Amazon SQS and more. In this case instead of writing data to persistent storage you're queueing it via APIs provided by the queue or job server. Processing is often put into a job handler class. Jobs from the queue are executed right after all jobs before it are done.

If nothing helps

If nothing helps, never assume what may fix performance problems. Always profile your code instead, before changing anything. The following tools may be helpful:

• Yii debug toolbar and debugger
• XDebug profiler
• XHProf