Question
Answer and Explanation
The question "Can you use PHP 7 Memcached with PHP 5?" is a bit misleading. It's not about compatibility between PHP versions and the Memcached server software itself. Memcached is a standalone, distributed memory object caching system, and it's generally agnostic to the programming language or version that interacts with it.
The crucial aspect here is the PHP client library used to connect to the Memcached server. The official `memcached` PHP extension is version-specific. For PHP 5 and PHP 7, different versions or branches of the extension are required. The PHP 7 extension is generally not compatible with PHP 5 and vice-versa. You CANNOT directly use the PHP 7 extension with PHP 5, or vice-versa.
Here’s a detailed breakdown:
1. The Memcached Server:
- The actual Memcached server application (e.g., `memcached`) can often be used across different versions of PHP. Its primary function is storing data in memory and doesn't care which language or version sends the requests, as long as they adhere to the Memcached protocol.
2. PHP Memcached Extensions:
- For PHP 5: You need to use a PHP 5 compatible version of the `memcached` extension (often older versions). Typically, you would install this via PECL: pecl install memcached-1.x (or similar version compatible with PHP 5).
- For PHP 7: You must use a PHP 7 compatible version of the `memcached` extension. Again, install via PECL: pecl install memcached (or use your OS package manager like `apt install php-memcached` or `yum install php-pecl-memcached`). It might be a more recent version, such as `3.x`.
3. What Happens if you try to use the wrong PHP Extension?
- If you attempt to load a PHP 7 `memcached` extension in PHP 5, you'll get fatal errors when your PHP interpreter tries to start. Usually PHP will crash or show errors in the logs indicating that a module was compiled for a different PHP version.
- The same happens when you try to load PHP 5 extension in PHP 7. It's compiled for older architecture and will lead to errors.
Key Takeaway:
You can use the same Memcached server instance with applications running PHP 5 and PHP 7. But you MUST use the correct corresponding PHP extension for each environment. They must be compiled against the PHP version that is running.
It's about ensuring that the PHP client extension (the actual module that your PHP code uses to communicate with Memcached) is compatible with the PHP version you are running. They must match.