Using Redis or Memcached instead of default file storage improves PHP session performance and scalability, reasons include: 1. The file locking mechanism is prone to blocking; 2. The session sharing is not supported across servers; 3. The cleaning mechanism is inflexible. Redis and Memcached are memory-based storage, fast speed, support expiration mechanisms, and are suitable for distributed environments. The configuration steps are: install the corresponding extension and modify the parameters such as session.save_handler and session.save_path in php.ini. Redis supports persistence and is more reliable, while Memcached is lighter and suitable for caching. Notes include: 1. Set the connection failure downgrade policy; 2. Ensure the safe generation of session ID; 3. Use prefix to avoid key conflicts; 4. Unified timeout settings; 5. You can temporarily switch back to the file storage debug session structure.

Using Redis or Memcached instead of the default file storage method can significantly improve performance and scalability when processing session data for PHP applications. Especially in multi-server environments, centralized session storage is a better choice.

Why not use the default file storage?

PHP stores sessions in temporary files on the server by default. This method is simple and easy to use, but there are obvious shortcomings in high concurrency or distributed deployment scenarios:

• File locking mechanism can easily cause blockage
• Not convenient to share session across servers
• The cleaning mechanism is inflexible and it is easy to accumulate invalid sessions

This is why we switch to Redis or Memcached - they are both memory-based storage, fast, support expiration mechanisms, and are naturally suitable for distributed environments.

Configure PHP to use Redis to store sessions

To allow PHP to save session to Redis, it mainly depends on phpredis or RedisSessionHandler extensions. Here are the basic steps:

• Install Redis extensions (for example via PECL)
• Modify php.ini configuration session processor to redis
• Set Redis connection address and port (such as tcp://127.0.0.1:6379)
• Optional setting of prefix, authentication password and other parameters

The example configuration is as follows:

 session.save_handler = redis
session.save_path = "tcp://127.0.0.1:6379?auth=password&prefix=PHPSESSID_"

Note that there may be slight differences between different versions of PHP and Redis extensions. It is recommended to check the official documentation to confirm the syntax format.

Configure PHP to use Memcached to store sessions

Memcached also supports session storage, but needs to install the memcached extension (not memcache) and then perform similar configuration.

Key configuration items include:

• session.save_handler = memcached
• session.save_path points to the Memcached address, such as "127.0.0.1:11211"
• You can set timeout, compression threshold and other behaviors through ini

Compared with Redis, Memcached is lighter and suitable for caching only scenarios, but it does not support persistence, so if the session data reliability is high, Redis is a better choice.

Frequently Asked Questions and Notes

Although switching to Redis or Memcached seems simple, there are still some details that need to be paid attention to in actual deployment:

• Degradation strategy for connection failure : Do not assume that Redis/Memcached is always available and do exception handling
• Generation and security of session ID : Ensure that the session.hash_function setting of PHP is reasonable
• Key name conflict problem : Use prefix to avoid mixing with other cached data
• Timeout settings are consistent : Make sure session.gc_maxlifetime and Redis/Memcached TTL settings match
• Debugging session data : You can temporarily change it back to the file handler to view the session content structure

Basically that's it. The entire process is not complicated, but certain configuration details are easily overlooked, especially when multiple service nodes are involved, consistency is particularly important.

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