Performance Tuning

Note: This section is under development.

The performance of your web application is based upon two parts. First is the framework performance and the second is the application itself. Yii has a pretty low performance impact on your application out of the box and can be fine-tuned further for production environment. As for the application, we'll provide some of the best practices along with examples on how to apply them to Yii.

Preparing environment

A well configured environment to run PHP application really matters. In order to get maximum performance:

  • Always use the latest stable PHP version. Each major release brings significant performance improvements and reduced memory usage.
  • Use APC for PHP 5.4 and less or Opcache for PHP 5.5 and more. It gives a very good performance boost.

Preparing framework for production

Disabling Debug Mode

First thing you should do before deploying your application to production environment is to disable debug mode. A Yii application runs in debug mode if the constant YII_DEBUG is defined as true in index.php. So, in order to disable debug mode, the following should be in your index.php:

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

Debug mode is very useful during development stage, but it would impact performance because some components cause extra burden in debug mode. For example, the message logger may record additional debug information for every message being logged.

Enabling PHP opcode cache

Enabling the PHP opcode cache improves any PHP application performance and lowers memory usage significantly. Yii is no exception. It was tested with both PHP 5.5 OPcache and APC PHP extension. Both cache optimize PHP intermediate code and avoid the time spent in parsing PHP scripts for every incoming request.

Turning on ActiveRecord database schema caching

If the application is using Active Record, we should turn on the schema caching to save the time of parsing database schema. This can be done by setting the Connection::enableSchemaCache property to be true via application configuration config/web.php:

return [
    // ...
    'components' => [
        // ...
        '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. Default is 'cache'.
            //'schemaCache' => 'cache',
        'cache' => [
            'class' => 'yii\caching\FileCache',

Note that the cache application component should be configured.

Combining and Minimizing Assets

It is possible to combine and minimize assets, typically JavaScript and CSS, in order to slightly improve page load time and therefore deliver better experience for end user of your application.

In order to learn how it can be achieved, refer to assets guide 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.

Improving application

Using Serverside Caching Techniques

As described in the Caching section, Yii provides several caching solutions that may improve the performance of a Web application significantly. If the generation of some data takes long time, we can use the data caching approach to reduce the data generation frequency; If a portion of page remains relatively static, we can use the fragment caching approach to reduce its rendering frequency; If a whole page remains relative static, we can use the page caching approach to save the rendering cost for the whole page.

Leveraging HTTP caching to save processing time and bandwidth

Leveraging HTTP caching saves both processing time, bandwidth and resources significantly. It can be implemented by sending either ETag or Last-Modified header in your application response. If browser is implemented according to HTTP specification (most browsers are), content will be fetched only if it is different from what it was prevously.

Forming proper headers is time consuming task so Yii provides a shortcut in form of controller filter [[yii\filters\HttpCache]]. Using it is very easy. In a controller you need to implement behaviors method like the following:

public function behaviors()
    return [
        'httpCache' => [
            'class' => \yii\filters\HttpCache::className(),
            'only' => ['list'],
            'lastModified' => function ($action, $params) {
                $q = new Query();
                return strtotime($q->from('users')->max('updated_timestamp'));
            // 'etagSeed' => function ($action, $params) {
                // return // generate etag seed here

In the code above one can use either etagSeed or lastModified. Implementing both isn't necessary. The goal is to determine if content was modified in a way that is cheaper than fetching and rendering that content. lastModified should return unix timestamp of the last content modification while etagSeed should return a string that is then used to generate ETag header value.

Database Optimization

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

Design index wisely in a database. Indexing can make SELECT queries much faster, but it may slow down INSERT, UPDATE or DELETE queries.

For complex queries, it is recommended to create a database view for it instead of issuing the queries inside the PHP code and asking DBMS to parse them repetitively.

Do not overuse Active Record. Although Active Record is good at modeling data in an OOP fashion, it actually degrades performance due to the fact that it needs to create one or several objects to represent each row of query result. For data intensive applications, using DAO or database APIs at lower level could be a better choice.

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

Using asArray

A good way to save memory and processing time on read-only pages is to use ActiveRecord's asArray method.

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

In the view you should access fields of each individual record from $posts as array:

foreach ($posts as $post) {
    echo $post['title'] . "<br>";

Note that you can use array notation even if asArray wasn't specified and you're working with AR objects.

Processing data in background

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 database. A console command that is run regularly via cron job queries database and processes data if there's any.

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

This issue could be solved by 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 queue or job server. Processing is often put into job handler class. Job from the queue is executed right after all jobs before it are done.

If nothing helps

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