Redis Data Types Explained: When and How to Use Them

Common Redis Data Types

Strings

Strings in Redis are a fundamental data type used for storing and retrieving string values.

Use Cases: Suitable for storing text or numbers, such as usernames, email addresses, or page counters. Strings can also store binary data, making them ideal for saving images or serialized objects.
Advantages: Simple operations with atomic actions like incrementing (INCR).

// Save a string
let _: () = conn.set("username", "alice").await.unwrap();

// Retrieve a string
let username: String = conn.get("username").await.unwrap();

Lists

Redis lists are collections of strings sorted by insertion order.

Use Cases: Ideal for implementing message queues, activity logs, or lists of recently accessed items. Lists support adding or removing elements from either end and can be used as stacks or queues.
Advantages: Fast insertion and deletion operations. Suitable for FIFO (First-In-First-Out) queues or LIFO (Last-In-First-Out) stacks.

// Add elements to the head of a list
let _: () = conn.lpush("events", "login").await.unwrap();
let _: () = conn.lpush("events", "logout").await.unwrap();

// Retrieve list elements
let events: Vec<String> = conn.lrange("events", 0, -1).await.unwrap();

Sets

Sets are unordered collections of unique strings.

Use Cases: Ideal for storing unique elements without a specific order, such as tags, visited IP addresses, or friend lists in a social network.
Advantages: Fast operations for adding, deleting, and checking the existence of elements. Supports set operations like union, intersection, and difference.

// Add elements to a set
let _: () = conn.sadd("tags", "redis").await.unwrap();
let _: () = conn.sadd("tags", "database").await.unwrap();

// Retrieve all set members
let tags: Vec<String> = conn.smembers("tags").await.unwrap();

Sorted Sets

Sorted sets are similar to sets but associate each member with a score.

Use Cases: Suitable for storing data that needs to be sorted by score, such as leaderboards, priority queues, or data with weighted sorting.
Advantages: Besides basic set operations, it supports retrieving elements by score or lexicographical order and fetching elements within specific ranges.

// Add elements to a sorted set
let _: () = conn.zadd("leaderboard", "alice", 100).await.unwrap();
let _: () = conn.zadd("leaderboard", "bob", 200).await.unwrap();

// Retrieve sorted set elements
let leaderboard: Vec<(String, f64)> = conn.zrange_withscores("leaderboard", 0, -1).await.unwrap();

Hashes

Hashes are collections of key-value pairs, similar to dictionaries or objects in programming languages.

Use Cases: Ideal for storing objects or multiple related data points, such as user attributes (name, age, email, etc.).
Advantages: Efficient for reading or writing multiple fields at once, making it suitable for representing objects or aggregating data points.

// Add key-value pairs to a hash
let _: () = conn.hset("user:100", "email", "alice@example.com").await.unwrap();

// Retrieve all key-value pairs from the hash
let user_info: HashMap<String, String> = conn.hgetall("user:100").await.unwrap();

Bitmaps

Bitmaps are arrays of bits where each bit can be independently set or queried.

Use Cases: Ideal for scenarios that require marking existence, such as user sign-ins or toggling feature statuses.
Advantages: Highly space-efficient for handling large volumes of boolean values.

// Set a bit in the bitmap
let _: () = conn.setbit("features", 0, true).await.unwrap();  // Enable feature 0

// Retrieve the value of a bit
let feature_enabled: bool = conn.getbit("features", 0).await.unwrap();

HyperLogLogs

HyperLogLog is a probabilistic data structure used for efficiently estimating the cardinality (the number of unique elements).

Use Cases: Ideal for estimating unique counts in large datasets, such as website unique visitors.
Advantages: Extremely memory-efficient compared to traditional counting methods, especially when handling large datasets.

// Add elements to a HyperLogLog
let _: () = conn.pfadd("pageviews", "user1").await.unwrap();
let _: () = conn.pfadd("pageviews", "user2").await.unwrap();

// Retrieve the approximate cardinality
let unique_pageviews: i64 = conn.pfcount("pageviews").await.unwrap();

Choosing Data Types

Selecting the appropriate Redis data type for backend operations is crucial for achieving optimal storage and retrieval efficiency. Understanding your data structure and use case is key. Below are common backend scenarios with recommended Redis data types:

User Sessions

Recommended Type: Hash
Reason: Hashes can store multiple properties of a user session object (e.g., user ID, token, last access time) and allow individual updates or retrievals.

let _: () = conn.hset("session:userid", "token", "abc123").await.unwrap();
let _: () = conn.hset("session:userid", "last_access", "2023-01-01").await.unwrap();

Real-time Messaging or Event Queuing

Recommended Type: List
Reason: Lists provide FIFO queue characteristics, suitable for real-time messaging or task queues.

let _: () = conn.rpush("events_queue", "event1").await.unwrap();
let event: String = conn.lpop("events_queue").await.unwrap();

Access Counters or Rate Limiting

Recommended Type: String
Reason: Strings support atomic increment operations, ideal for counters.

let _: () = conn.incr("page_view_count", 1).await.unwrap();
let count: i64 = conn.get("page_view_count").await.unwrap();

Leaderboards or Score Sorting

Recommended Type: Sorted Set
Reason: Sorted sets automatically sort data based on scores, perfect for leaderboards or any sorted data.

let _: () = conn.zadd("leaderboard", "user123", 2500).await.unwrap();
let leaderboard: Vec<(String, f64)> = conn.zrange_withscores("leaderboard", 0, -1).await.unwrap();

Unique Value Collections like Tags or Categories

Recommended Type: Set
Reason: Sets provide unique value storage, suitable for deduplication scenarios.

let _: () = conn.sadd("tags", "redis").await.unwrap();
let tags: Vec<String> = conn.smembers("tags").await.unwrap();

Multi-attribute Object Storage

Recommended Type: Hash
Reason: Hashes can store multiple fields of an object and allow independent access or updates.

let _: () = conn.hset("user:100", "name", "Alice").await.unwrap();
let user: HashMap<String, String> = conn.hgetall("user:100").await.unwrap();

Feature Flags or Toggles

Recommended Type: Bitmap
Reason: Bitmaps are ideal for storing boolean states like feature toggles.

let _: () = conn.setbit("features", 1, true).await.unwrap();
let feature_on: bool = conn.getbit("features", 1).await.unwrap();

Conclusion

Choosing the right type depends on your specific needs. If your data structure is simple (like a single key-value pair), a string may suffice. For more complex structures, like user profiles or session information, hashes may be better. If your application involves leaderboards or sorted data, use sorted sets accordingly.