How to create Bloom filters in Redis

A Bloom filter is a space-efficient probabilistic data structure used to test whether a given element is a member of a set. Redis, being a key-value store, doesn't have native support for Bloom filters.

Here, we can implement Bloom filters in Redis using commands like BF.ADD, BF.MADD, and BF.MEXISTS. These commands are described below:

Implementing the BF.ADD command

Let’s suppose we want to create a Bloom filter denoted as myfilter. To start off, we will use the BF.ADD command to create a Bloom filter with the name myfilter.

We need to add a couple of items to make this Bloom filter functional. Therefore, we’ll add two items item1 and item2 one after the other with the following commands:

The output should return a boolean index 1, indicating that the addition of these items to the Bloom filter was successful.

Adding multiple items with BF.MADD

For adding multiple items in one command, we can use the BF.MADD command:

Running this in the terminal should also return a boolean index 1 as the output for both items:

Note: When we try to add an item that is already in the filter using BF.MADD, it will return the boolean index 0 because it cannot be added again.

Checking for item membership

To verify whether these items are inside the Bloom filter myfilter, we can use the BF.EXISTS command with the name of the item we want to check:

Note: In the place of item1, we can write the name of any item we want to check for membership.

In this case, the output should be a boolean index 1, confirming that item1 is a member of the Bloom filter myfilter:

On the other hand, if an item (say item3) does not exist in the Bloom filter, a boolean index 0 will be returned in the output.

Verifying the membership of multiple items with BF.MEXISTS

Similar to the case where we added multiple items under one command, we can also verify their membership in one command via the BF.MEXISTS command:

The output in the terminal will also return a boolean index 1 for an existing item in the Bloom filter and 0 otherwise:

Try it yourself

These commands can be tested with the terminal widget below. Have fun exploring!

Conclusion

In conclusion, Redis provides a powerful and efficient implementation of Bloom filters through the RedisBloom module. By leveraging commands like BF.ADD, BF.MADD, and BF.MEXISTS, developers can easily create and manage Bloom filters for membership tests. Make sure to check out the Redis command documentation for further usage information.