How to correctly set the number of PHP processes

In a high-traffic web application, in order to better handle user requests, we usually use multiple processes to handle multiple requests at the same time. In PHP, using FPM (FastCGI Process Manager) for multi-process management is a common way. However, if our web server has too many processes, it will place too much burden on the server's resources when processing large traffic, causing the server to crash. Therefore, it is very important to configure the PHP process manager correctly. This article explains how to correctly set the number of PHP processes.

1. Understanding the PHP Process Manager

Before configuring the number of PHP processes, we need to understand the PHP Process Manager and how it works.

FPM is a PHP FastCGI manager that can manage all PHP processes and provides multiple process pools. Each process pool has a specific number of PHP processes, which can be specified or calculated based on the server's CPU and memory.

When a request for a PHP file is made, Nginx or Apache will forward the request to the FPM manager, which will select one of the PHP processes based on the load balancing algorithm. The PHP process executes the code and sends the response back to Nginx or Apache, which is ultimately returned to the client.

2. Select the number of PHP processes

It is very important to select the number of PHP processes according to the actual situation. If the number of processes is too small, it may not be able to withstand the load of high traffic; if the number of processes is too many, server resources will be wasted.

We can estimate the number of PHP processes required by the server through the following formula:

max_children = ((Total RAM - Memory used by other processes) / Memory consumed by one PHP child process)

Among them,

max_children is the maximum number of PHP child processes.
Total RAM is the total amount of memory on the server.
Memory used by other processes is the amount of memory occupied by other processes, which can be viewed using the top or ps command.
Memory consumed by one PHP child process is the memory footprint of each PHP process, which can be estimated using the following command.

php -r 'echo memory_get_usage(true);'

This will return an integer in bytes. To convert this to MB, divide that number by 1024 x 1024 to get the amount of memory consumed by each PHP process.

3. Adjust the number of PHP processes

We can specify the number of processes in the php.ini file and adjust these numbers based on the availability of server resources.

In the php.ini file, you can find the following parameters:

pm = dynamic
pm.max_children = 20
pm.start_servers = 2
pm.min_spare_servers = 1
pm.max_spare_servers = 3

These are key parameters that affect the PHP process. pm represents the process manager (the dynamic process manager is used here), pm.max_children represents the maximum number of child processes, pm.start_servers represents the number of child processes when enabled, pm.min_spare_servers represents the number of reserved child processes, pm.max_spare_servers represents The maximum number of idle processes that can be created.

After estimating based on the formula in the second step, set pm.max_children to the corresponding value and adjust other parameters based on the availability of server resources.

4. Monitor and tune the number of processes

Once the number of processes is configured and set, we need to monitor them regularly to ensure that they are functioning properly under full or light load conditions run.

You can use the top or htop command to monitor the running status of the server. These tools will display all processes on the server and their resource utilization.

If we find that the number of processes is too many or too few, we can adjust the number of processes according to the actual situation and observe whether their operating conditions improve.

5. Summary

In high-load web applications, it is very important to correctly configure the number of PHP processes. We can use the above method to estimate the number of processes required by the server and determine the best strategy for tuning parameters. Regularly monitoring the number of PHP processes is another key factor in ensuring that your application runs stably under high traffic loads.

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