Welcome! Today, we will explore the powerful concept of Redis sets in C#. Redis sets are collections of unique, unordered string elements stored in a Redis database. They are highly efficient for operations like checking if an item exists, adding or removing items, and retrieving all members. This is useful for managing unique data efficiently, like tracking unique user actions or storing distinct data entries without duplication across distributed applications.

In this lesson, you will learn how to use Redis sets in C#. Specifically, we will cover how to:

1. Add items to a Redis set.
2. Retrieve items from a Redis set.

Redis sets are collections of unique, unordered string elements stored in Redis. They provide efficient operations with time complexity of $O(1)$ for adding, removing, and checking membership. Redis sets are particularly powerful in distributed systems where multiple applications need to share and manipulate the same unique data collections.

Let's start by creating a Redis set and adding some items to it:

This example demonstrates how to handle Redis sets in C# and perform basic operations on them.

Let's break down the code:

• We import the StackExchange.Redis namespace to work with Redis.
• We establish a connection to Redis using ConnectionMultiplexer.Connect().
• We get a database reference using .

The db.SetMembers method is part of the StackExchange.Redis library used to retrieve all the members of a set stored in Redis.

Parameters:

• RedisKey key: The key of the set you want to retrieve members from (e.g., "countries").
• CommandFlags flags: Optional parameter to modify the command's behavior. Typically, you can use the default value.

Return Value: Returns an array of RedisValue, which contains all the members of the specified set.

Important Notes:

• Redis sets store unique elements, so SetMembers will return each element only once.
• The elements in a Redis set are unordered, so the order of elements in the returned array is not guaranteed.
• The time complexity is $O(N)$ where N is the number of elements in the set.

Apart from adding and retrieving elements, we can perform other operations, such as checking the size of the set and removing an item:

In this snippet, we use the SetLength method to get the number of items in the Redis set and the SetRemove method to delete an item from the set.

Using Redis sets effectively in C# is important for several reasons:

1. Distributed Efficiency: Redis sets allow rapid membership checking across multiple applications, enabling fast verification of whether an item is part of the set in distributed systems.
2. Persistence: Unlike in-memory collections, Redis sets persist data and can be shared across application restarts and multiple instances.
3. Real-World Applications: Redis sets are suitable for tracking unique items like active user sessions, distinct tags, or managing distributed locks.

Mastering Redis sets equips you with the tools to handle various unique item use cases efficiently in distributed applications. Now, it's time to get hands-on and practice by working through some exercises!