Welcome back! In this lesson, we will explore a crucial feature of Redis: key expiration. This builds on our Redis knowledge from previous lessons and adds another tool to our kit for managing data efficiently in high-performance applications. This is useful for various situations, such as caching data, managing session lifetimes, or any scenario where you want data to automatically expire after a certain period. We will learn how to set expiration times on keys and check the remaining time-to-live (TTL) for a key.

To set a key with an expiration time, you can use the setex method in PHP:

The above code snippet shows how to set a key (session:12345) with a value (data) that expires after 2 seconds.

To check the remaining time-to-live (TTL) for a key, you can use the ttl method with the key name as the parameter. The ttl method can return negative values in certain cases:

• -1: The key exists but does not have an expiration set.
• -2: The key does not exist (it could have expired, be manually deleted or it never existed).

Key expiration is an essential feature for managing limited memory resources efficiently. By setting expiration times, you can ensure that outdated data is removed automatically without manual intervention. This can significantly improve your application's performance and reliability.

By mastering key expiration, you can build more intelligent caching mechanisms, manage user sessions effectively, and handle temporary data seamlessly. This concept is a critical aspect of maintaining high-performance applications that need to run efficiently over time.

Exciting, right? Let's move on to the practice section and start applying these concepts hands-on.