Redis HyperLogLog

It works closely similar to a Redis filter bloom but with a different implementation.

There are three main commands when working with Redis HyperLogLogs. These commands include:

1. PFADD command
2. PFCOUNT command
3. PFMERGE command.

Let us take an example.

PFADD Command

Assume we have a database that holds the type of databases that we support. We can add each entry to the HyperLogLog as:

127.0.0.1:6379> PFADD databases MySQL
(integer) 1
127.0.0.1:6379> PFADD databases MongoDB
(integer) 1
127.0.0.1:6379> PFADD databases PostgreSQL
(integer) 1
127.0.0.1:6379> PFADD databases Oracle
(integer) 1

PFCOUNT Command

To see the number of databases supported, we can run:

127.0.0.1:6379> PFCOUNT databases
(integer) 4

PFMERGE Command

Let us also assume that we have a list of unsupported databases:

127.0.0.1:6379> PFADD unsupported Elasticsearch Solr Neo4j Memcached
(integer) 1

To create a union of both supported and unsupported databases, we can use the PFMERGE command as shown:

127.0.0.1:6379> PFMERGE all databases unsupported
OK

We can then count the number of databases in the new key as:

127.0.0.1:6379> PFCOUNT all
(integer) 8

Closing

This tutorial covered how to work with Redis HyperLogLog using PFADD, PFCOUNT, and PFMERGE commands.