What Data Structure Does Redis Use?


Angela Bailey

In this article, we will explore the data structure used by Redis, a popular in-memory data store. Understanding the underlying data structure is crucial for optimizing performance and leveraging the full potential of Redis.

Introduction to Redis

Redis is an open-source, in-memory key-value store that can be used as a database, cache, or message broker. It offers high-performance and low-latency access to data by storing it entirely in memory. Redis supports various data structures, allowing it to handle different types of data efficiently.

The Data Structure

Redis uses a wide array of data structures to cater to different use cases. Let’s dive into some of the most commonly used ones:


The simplest and most basic data structure in Redis is the string. It can hold any binary data up to 512MB in size. Strings are commonly used for caching values or as counters.


Lists are collections of strings that are ordered based on insertion order. They allow for efficient addition and removal of elements at both ends, making them suitable for building queues or stacks.

To illustrate:

  <li>LPUSH mylist "world"</li>
  <li>LPUSH mylist "hello"</li>

This code snippet adds two elements, “hello” and “world”, to the list named “mylist”. The resulting list would look like [“hello”, “world”].


Sets are unordered collections of unique strings. They provide fast membership tests and allow performing operations like union, intersection, and difference between sets. Sets are useful for implementing tags or tracking unique items.

Here’s an example:

  <li>SADD myset "hello"</li>
  <li>SADD myset "world"</li>

This code snippet adds two elements, “hello” and “world”, to the set named “myset”. The resulting set would contain only unique values.


Hashes store field-value pairs. They are useful for representing objects or records with multiple attributes. Hashes provide efficient access to individual fields and can handle millions of fields per hash.

Consider this example:

  <li>HSET user:1 name "John Doe"</li>
  <li>HSET user:1 age "30"</li>

This code snippet creates a hash to represent a user with the fields “name” and “age”. Each field is associated with a value.

Sets Sorted by Score (Sorted Sets)

Sorted Sets are similar to sets but with an additional associated score. The elements in a sorted set are ordered based on the scores, allowing for efficient retrieval of elements within a specific range. Sorted sets are commonly used for leaderboard implementations or ranking systems.

Let’s look at an example:

  <li>ZADD leaderboard 100 "John"</li>
  <li>ZADD leaderboard 200 "Jane"</li>

This code snippet adds two elements, “John” and “Jane”, to the sorted set named “leaderboard” with their respective scores. The elements are automatically sorted based on the scores.


Redis’s versatility is attributed to its rich collection of data structures. By leveraging the appropriate data structure for your use case, you can optimize performance and unlock the full potential of Redis. Whether it’s strings, lists, sets, hashes, or sorted sets, understanding these data structures will help you make the most out of Redis in your applications.

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