How does the method of storing session IDs affect server load and performance in PHP?

Storing session IDs in a server-side file system can lead to increased server load and decreased performance due to the overhead of reading and writing to the file system. To improve performance, it is recommended to store session IDs in a more efficient manner such as using a database or in-memory storage like Redis.

// Use Redis to store session IDs for improved performance
ini_set('session.save_handler', 'redis');
ini_set('session.save_path', 'tcp://127.0.0.1:6379');

session_start();