Performance Tuning

Performance of Web applications is affected by many factors. Database access, file system operations, network bandwidth are all potential affecting factors. Yii has tried in every aspect to reduce the performance impact caused by the framework. But still, there are many places in the user application that can be improved to boost performance.

1. Enabling APC Extension ¶

Enabling the PHP APC extension is perhaps the easiest way to improve the overall performance of an application. The extension caches and optimizes PHP intermediate code and avoids the time spent in parsing PHP scripts for every incoming request.

2. Disabling Debug Mode ¶

Disabling debug mode is another easy way to improve performance. An Yii application runs in debug mode if the constant YII_DEBUG is defined as true. Debug mode is 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.

3. Using yiilite.php ¶

When the PHP APC extension is enabled, we can replace yii.php with a different Yii bootstrap file named yiilite.php to further boost the performance of an Yii-powered application.

The file yiilite.php comes with every Yii release. It is the result of merging some commonly used Yii class files. Both comments and trace statements are stripped from the merged file. Therefore, using yiilite.php would reduce the number of files being included and avoid execution of trace statements.

Note, using yiilite.php without APC may actually reduce performance, because yiilite.php contains some classes that are not necessarily used in every request and would take extra parsing time. It is also observed that using yiilite.php is slower with some server configurations, even when APC is turned on. The best way to judge whether to use yiilite.php or not is to run a benchmark using the included hello world demo.

4. Using 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.

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 configuring the CDbConnection::schemaCachingDuration property to be a value greater than 0.

Besides these application-level caching techniques, we can also use server-level caching solutions to boost the application performance. As a matter of fact, the APC caching we described earlier belongs to this category. There are other server techniques, such as Zend Optimizer, eAccelerator, Squid, to name a few.

5. 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 modelling 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.

6. Minimizing Script Files ¶

Complex pages often need to include many external JavaScript and CSS files. Because each file would cause one extra round trip to the server and back, we should minimize the number of script files by merging them into fewer ones. We should also consider reducing the size of each script file to reduce the network transmission time. There are many tools around to help on these two aspects.

For a page generated by Yii, chances are that some script files are rendered by components that we do not want to modify (e.g. Yii core components, third-party components). In order to minimizing these script files, we need two steps.

Note: The scriptMap feature described in the following has been available since version 1.0.3.

First, we declare the scripts to be minimized by configuring the scriptMap property of the clientScript application component. This can be done either in the application configuration or in code. For example,

$cs=Yii::app()->clientScript;
$cs->scriptMap=array(
    'jquery.js'=>'/js/all.js',
    'jquery.ajaxqueue.js'=>'/js/all.js',
    'jquery.metadata.js'=>'/js/all.js',
    ......
);

What the above code does is that it maps those JavaScript files to the URL /js/all.js. If any of these JavaScript files need to be included by some components, Yii will include the URL (once) instead of the individual script files.

Second, we need to use some tools to merge (and perhaps compress) the JavaScript files into a single one and save it as js/all.js.

The same trick also applies to CSS files.

We can also improve page loading speed with the help of Google AJAX Libraries API. For example, we can include jquery.js from Google servers instead of our own server. To do so, we first configure the scriptMap as follows,

$cs=Yii::app()->clientScript;
$cs->scriptMap=array(
    'jquery.js'=>false,
    'jquery.ajaxqueue.js'=>false,
    'jquery.metadata.js'=>false,
    ......
);

By mapping these script files to false, we prevent Yii from generating the code to include these files. Instead, we write the following code in our pages to explicitly include the script files from Google,

<head>
<?php echo CGoogleApi::init(); ?>
 
<?php echo CHtml::script(
    CGoogleApi::load('jquery','1.3.2') . "\n" .
    CGoogleApi::load('jquery.ajaxqueue.js') . "\n" .
    CGoogleApi::load('jquery.metadata.js')
); ?>
......
</head>