Introduction to File Handling with C# Streams

Welcome back! In this lesson, we will explore a crucial feature of Redis: key expiration. This topic builds on our Redis knowledge and adds another tool to our kit for managing data efficiently in high-performance applications.

You will learn how to set expiration times on your Redis keys. This is useful for many 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.

Here's a quick preview of what you will be doing:

To set a key with an expiration time, you can use the StringSet method with an expiry parameter:

using StackExchange.Redis;
using System;
using System.Threading;

public class Program
{
    public static void Main(string[] args)
    {
        ConnectionMultiplexer redis = ConnectionMultiplexer.Connect("localhost");
        IDatabase db = redis.GetDatabase();

        string key = "session:12345";
        db.StringSet(key, "data", TimeSpan.FromSeconds(2));
        string value = db.StringGet(key);
        Console.WriteLine($"Value: {value}");  // data

        TimeSpan? ttl = db.KeyTimeToLive(key);
        Console.WriteLine($"Time-to-live for session key: {ttl?.Seconds} seconds");

        Thread.Sleep(3000);
        value = db.StringGet(key);
        Console.WriteLine($"Value: {value}");  // None
    }
}

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 KeyTimeToLive method with the key name as the parameter.

After waiting for the expiration time, you can verify that the key no longer exists. This code waits 3 seconds and then attempts to get the value of the key, which should return null because the key has expired.

Another useful method is KeyExpire, which allows you to set the expiration time for a key after it has been created:

db.StringSet(key, "data");
db.KeyExpire(key, TimeSpan.FromSeconds(2));

This code snippet sets the key session:12345 with a value of data and then sets the expiration time to 2 seconds. We will explore this method in more detail in the practice section.