Redis Bitmaps

A bitmap is simply an array of bits. Therefore, it is commonly known as a bit array or bit vector. It is one of the data structures that makes Redis quite flexible and extensive out of the box. If you need to store a map of boolean information in a compact space, bitmaps will be your default choice.

Let us discuss how to use bitmaps in Redis using this tutorial.

Redis Bitmaps

Before diving into the actual commands and store bitmaps, few things to note.

A Bitmap is not a native data type in Redis. In actuality, they are a set of bit-oriented operations built on the String type.

Bit operations are categorized into two main groups:

  1. Constant-time single-bit operations.
  2. Group bit operations.

An example of a single-bit operation is setting a bit from 1 to 0 or retrieving the value of a bit.

A group bit operation can involve a process such as getting the number of bits within a specific range.

Redis Create Bitmap

To create a key holding a bitmap in Redis, we use the SETBIT command. The command takes the name of the key, offset value, and the actual bit as arguments.

The syntax is as shown:> SETBIT key offset bit

If the specified key does not exist, Redis will create a new one that can hold a bit at a specified offset.

The offset value must be greater than or equal to 0 but less than 2^32. This is because bitmaps are limited to 512MB.

RECAP: A bit represents the most basic unit of information and holds two possible values. In simple terms, a bit is used to describe logical stateful information such as yes/no, 1/0, +/-, etc.

Examples are shown below.[10]> SETBIT bitkey 2 1

(integer) 0[10]> SETBIT bitkey 2 0

(integer) 1

Redis Count Number of Set Bits

To determine the number of set bits in Redis, use the BITCOUNT command. Take the example.[10]> SETBIT bitkey 3 1[10]> SETBIT bitkey 4 1[10]> SETBIT bitkey 5 1[10]> SETBIT bitkey 6 1[10]> SETBIT bitkey 7 1

To get the number of set bits, run:[10]> BITCOUNT bitkey

(integer) 5

This should return the number of set bits as an integer.

NOTE: A set bit refers to any bit whose value is set to 1.

Redis Bitwise Operations

We can perform bitwise operations using the BITOP command. For example, to achieve a bitwise AND operation, we can do:[10]> SETBIT bitkey2 3 1

(integer) 0

In the example above, we create a new bitmap and call it bitkey2.

We can then perform the bitwise AND operation as shown:[10]> BITOP AND bitkey bitkey2

(integer) 1

To get the keys, run:[10]> GET bitkey2


Redis Retrieve Bit Value

To get the bit value stored at a specific offset, use the GETBIT command followed by the target offset.

An example is as shown:[10]> GETBIT bitkey 3

(integer) 1

If the bit at the specified offset is not set, the command returns 0 as shown:[10]> GETBIT bitkey 200

(integer) 0


In this article, we covered the fundamentals of bitmaps and how to use them in Redis. Check the docs to learn more.

Thanks for reading!!

About the author

John Otieno

My name is John and am a fellow geek like you. I am passionate about all things computers from Hardware, Operating systems to Programming. My dream is to share my knowledge with the world and help out fellow geeks. Follow my content by subscribing to LinuxHint mailing list