In this post, we're going to explore how to implement a user leaderboard system using Redis. The leaderboard will keep track of user scores and profile information such as username and avatar.
Introduction
Redis is a powerful in-memory data structure store that is used as a database, cache, and message broker. We'll be leveraging two particular data types in Redis: sorted sets and hashes.
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Sorted Sets: In Redis, a sorted set is a data type that has a set of unique elements where each element is associated with a score. It provides us with an efficient way to maintain a list of elements based on their scores, which is perfect for a leaderboard system.
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Hashes: Redis hashes are the perfect data structure to store object-like items. We'll use hashes to store user's information like username, avatar type, etc.
Let's Get Started
First, ensure you have Redis installed and running on your system.
Storing and Retrieving User Scores
We use the ZADD command to add users to the sorted set. The command takes the sorted set name, the score, and the user's ID. For example, to add a user with the ID 'user1' and a score of 150, we can use:
ZADD leaderboard 150 user1
To retrieve the scores in descending order (highest score first), we can use the ZREVRANGE command with the WITHSCORES option:
ZREVRANGE leaderboard 0 -1 WITHSCORES
Conditionally Updating Scores
In many cases, we want to update a user's score only if the new score is higher than the existing one. Redis allows us to do this easily with the ZADD command by adding the XX GT option:
ZADD leaderboard XX GT 200 user1
This command will update 'user1's score to 200 only if 200 is greater than their current score.
Storing and Retrieving User Information
We can use the HSET command to store user information. For example, to set the username and avatar type for 'user1':
HSET user:user1 username "John Doe" avatar "TypeA"
To retrieve this information, we can use the HGETALL command:
HGETALL user:user1
Tying It All Together
Before we look at the specific commands to update both the sorted set and hash when a user achieves a new score, let's visualize the whole flow with the diagram below:
This diagram depicts the flow as follows:
- The user achieves a new score and sends it to the application.
- The application updates the user's info in the Redis hash.
- The application also updates the score in the Redis Sorted Set (the leaderboard).
- The Redis hash and sorted set return the updated user info and leaderboard to the application.
- The application displays the updated leaderboard to the user.
Now that we know how to store and retrieve user scores and profile information, we can tie it all together.
When a user achieves a new score, we can update both the sorted set and the hash:
ZADD leaderboard XX GT 200 user1
HSET user:user1 username "John Doe" avatar "TypeB"
To display the leaderboard, we first retrieve the user IDs and scores:
ZREVRANGE leaderboard 0 -1 WITHSCORES
For each user ID, we then retrieve the user information:
HGETALL user:user1
Conclusion
That's it! We've created a simple but effective leaderboard system using Redis' sorted sets and hashes. Redis is a powerful tool for such use cases due to its speed and efficient data structures.
