How Does a PHP Server Handle Multiple Simultaneous Requests to the Same Script?

Simultaneous Requests to PHP Script

When a PHP engine executes a script on a server, multiple simultaneous browser requests may be made to the same script. The behavior of these requests depends on the server configuration.

Server Configuration

Usually, the server can handle several hundred requests concurrently. The Apache configuration option MaxClients limits the number of simultaneous requests. When the limit is reached, requests may be queued based on the ListenBacklog configuration.

Request Handling

Queued Requests:
Requests are typically not queued unless:

• There is a lock, e.g., in file-based sessions when multiple requests from the same client attempt to open the same session file concurrently.
• Requests originate from the same client and browser, where browsers may queue requests independently.
• The number of active processes exceeds MaxClients.

Ignored Requests:
Requests are not typically ignored. Multiple users can access the same website simultaneously without encountering issues.

Script Instance

There is no concept of a "script instance." Each request is handled by a separate process that forks from the webserver and reads the PHP script from disk. Multiple processes can read the script concurrently without interference, as the file is loaded into distinct memory blocks for each process.

Conclusion

Simultaneous requests to PHP scripts are typically handled efficiently by the server configuration, ensuring that multiple users can access the website without significant delays.

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