Understanding of PHP memory overflow, command line and web service execution methods

This article mainly introduces the understanding of the two execution methods of PHP memory overflow, command line and Web service. It has certain reference value. Now I share it with you. Friends in need can refer to it

During the development process, due to an excessive amount of data read from the database, a certain interface returned a status of 200 but no response data. The PHP error log contained the following information: PHP Fatal error: Allowed memory size of 134217728 bytes exhausted.

Obviously this is an error caused by memory overflow (Out Of Memory), but what puzzles me is that there is no output in the business log (application.log) of the Yii framework, and there is no Stack Trace on the page. error message, so we traced the cause.

The reason is as follows, first look at the core code of the Yii framework CApplication.php file:

public function run()
{    if($this->hasEventHandler('onBeginRequest'))        
$this->onBeginRequest(new CEvent($this));
    register_shutdown_function(array($this,'end'),0,false);    
    $this->processRequest();    
    if($this->hasEventHandler('onEndRequest'))        
    $this->onEndRequest(new CEvent($this));
}

Used register_shutdown_function before processing the request to register the callback when abnormal termination, normally speaking , PHP will call back the end() method when an abnormal script terminates. In the listener of the onEndRequest event, you can use error_get_last() to obtain this error.

However, when OOM occurs, the Linux Out Of Memory killer will execute kill -9 to send the SIGKILL signal. According to the instructions in the PHP manual, the SIGKILL signal cannot be captured and intercepted. The PHP script will exit directly without any cleanup code. Neither will be executed, so the register_shutdown_function method will not work, and naturally there will be no subsequent logging, error page display and other processes.

In addition, I noticed a phenomenon during development: OOM will occur when accessing through the Web, but no error will be reported when executing through the Console.

It can be seen that there is a difference between the two methods. When accessing the Web, the PHP script process is started by PHP-FPM and is also restricted by the FPM configuration file. The configuration file in /etc/php-fpm.d has php_admin_value[memory_limit] = 128M limit. So simply increasing the memory_limit in php.ini has no effect when accessing via the web.

Console mode execution does not go through PHP-FPM, so it is only limited by the memory parameters configured in php.ini, and the memory_limit configured in the development machine => 512M => 512M, so it will not OOM is generated.

There is a question here. From the perspective of implementation principles, how does PHP-FPM manage the PHP process? Does PHP-FPM really use kill -9 to kill the PHP script process?

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Attached is the calling relationship between WebServer, PHP-FPM, and PHP scripts:

The request first enters the Web server (such as Nginx), and Nginx distributes the request (according to server node, location node, etc. configuration):

1. Requesting static resources does not require FastCGI processing, and goes directly to the corresponding file location

2. Required for dynamic requests For PHP code processing, you need to hand the request to the program that implements the FastCGI protocol (PHP-FPM)

You can see this configuration information in Nginx: "fastcgi_pass 127.0.0.1:9000 ;", execute the command "lsof -i:9000" and you can see that port 9000 happens to be the PHP-FPM process.

Nginx passes the request information to PHP-FPM, and PHP-FPM allocates a Worker process for processing. The Worker process registers variables $_GET/$_POST, etc., and accesses the specified PHP according to the request information. The script file is then executed using the PHP interpreter.
(My understanding is: equivalent to PHP-FPM starting the PHP interpreter, a bit like executing the php -f script.php command)

Information layers of network requests Passed, and finally reaches PHP, so various parameters of this HTTP request can be obtained in the PHP code.

Nginx tells PHP-FPM which PHP script to execute. A line can be seen in the Nginx configuration:

fastcgi_param SCRIPT_FILENAME /home/dev_user/www/xxx/webroot/index.php;

If you do not specify a PHP file, the default configuration will be used. Try to use the one in the root directory. index.php file. The framework program will be started in index.php, and the framework will find the corresponding Controller and Action to complete the actual business logic.

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