Easy Tutorial
Sorted Sets Zrevrangebyscore Hashes Hget Hyperloglog Pfcount Strings Msetnx Redis Partitioning Connection Select Redis Geo Lists Lset Server Config Resetstat Sets Sismember Lists Brpop Strings Getbit Keys Randomkey Strings Setex Server Client Getname Pub Sub Punsubscribe Strings Incrby Sorted Sets Zincrby Keys Dump Sets Spop Strings Get Strings Psetex Lists Lrange Redis Sets Server Command Getkeys Strings Decr Strings Incr Redis Transactions Lists Lpop Sorted Sets Zrank Keys Pexpireat Scripting Script Load Sorted Sets Zunionstore Scripting Script Exists Hashes Hexists Keys Expireat Sets Sinterstore Keys Del Keys Move Sorted Sets Zscore Lists Llen Server Info Server Debug Object Sorted Sets Zremrangebylex Server Config Rewrite Sets Sdiffstore Pub Sub Subscribe Redis Keys Server Client Pause Strings Strlen Redis Backup Keys Ttl Sorted Sets Zrange Redis Strings Sets Sdiff Hashes Hmget Sorted Sets Zcard Connection Quit Strings Setrange Server Flushall Keys Renamenx Server Config Set Connection Ping Lists Brpoplpush Sets Sinter Server Flushdb Redis Intro Server Client List Keys Type Server Sync Keys Pexpire Sorted Sets Zremrangebyscore Keys Rename Java Environment Setup Transactions Discard Redis Lists Server Client Setname Server Role Hashes Hsetnx Redis Sorted Sets Keys Persist Transactions Watch Lists Ltrim Server Client Kill Strings Getset Sets Smove Lists Lpushx Sorted Sets Zscan Connection Echo Strings Mget Sorted Sets Zlexcount Redis Hyperloglog Sorted Sets Zadd Sets Srandmember Redis Pipelining Transactions Multi Hashes Hdel Hashes Hkeys Pub Sub Psubscribe Keys Exists Sorted Sets Zremrangebyrank Sorted Sets Zrevrange Lists Rpushx Server Debug Segfault Hashes Hvals Server Bgrewriteaof Sets Sscan Strings Mset Keys Pttl Connection Auth Strings Incrbyfloat Keys Expire Sorted Sets Zrangebylex Hashes Hmset Sets Scard Sorted Sets Zrevrank Strings Decrby Server Lastsave Server Cluster Slots Redis Commands Redis Install Server Save Server Config Get Redis Hashes Keys Keys Hashes Hincrbyfloat Redis Data Types Strings Setbit Redis Benchmarks Hyperloglog Pfmerge Sorted Sets Zrem Transactions Exec Server Command Info Pub Sub Unsubscribe Transactions Unwatch Strings Getrange Hashes Hincrby Sorted Sets Zrangebyscore Redis Pub Sub Sets Smembers Lists Lindex Scripting Eval Sets Sadd Hyperloglog Pfadd Lists Lrem Redis Tutorial Server Slowlog Lists Blpop Pub Sub Publish Lists Linsert Scripting Evalsha Sets Sunionstore Redis Conf Server Command Count Sorted Sets Zcount Server Monitor Sorted Sets Zinterstore Server Command Server Dbsize Hashes Hlen Scripting Script Flush Server Slaveof Keys Scan Redis Connection Hashes Hset Redis Server Redis Scripting Lists Rpop Redis Client Connection Scripting Script Kill Redis Security Server Time Strings Append Redis Java Server Showlog Server Shutdown Lists Rpush Lists Rpoplpush Lists Lpush Server Bgsave Sets Srem Strings Setnx Redis Stream Hashes Hscan Redis Php Pub Sub Pubsub Hashes Hgetall Strings Set Sets Sunion
❮ Sorted Sets Zlexcount Sorted Sets Zadd ❯

Redis HyperLogLog

Redis introduced the HyperLogLog structure in version 2.8.9.

Redis HyperLogLog is an algorithm for cardinality estimation. The advantage of HyperLogLog is that it always requires a fixed and very small amount of space to compute the cardinality, even when the number or volume of input elements is extremely large.

In Redis, each HyperLogLog key consumes only 12 KB of memory to estimate the cardinality of nearly 2^64 distinct elements. This contrasts sharply with sets, where the memory consumption increases with the number of elements when computing cardinality.

However, since HyperLogLog only calculates the cardinality based on the input elements and does not store the elements themselves, it cannot return the individual elements like a set.

What is Cardinality?

For example, given the dataset {1, 3, 5, 7, 5, 7, 8}, the cardinality set would be {1, 3, 5, 7, 8}, and the cardinality (unique elements) is 5. Cardinality estimation is the process of quickly calculating the cardinality within an acceptable margin of error.

Example

The following example demonstrates the working process of HyperLogLog:

redis 127.0.0.1:6379> PFADD tutorialprokey "redis"

1) (integer) 1

redis 127.0.0.1:6379> PFADD tutorialprokey "mongodb"

1) (integer) 1

redis 127.0.0.1:6379> PFADD tutorialprokey "mysql"

1) (integer) 1

redis 127.0.0.1:6379> PFCOUNT tutorialprokey

(integer) 3

Redis HyperLogLog Commands

The table below lists the basic commands for Redis HyperLogLog:

No. Command and Description
1 PFADD key element [element ...] <br>Adds the specified elements to the HyperLogLog.
2 PFCOUNT key [key ...] <br>Returns the estimated cardinality for the given HyperLogLog.
3 PFMERGE destkey sourcekey [sourcekey ...] <br>Merges multiple HyperLogLogs into one.
❮ Sorted Sets Zlexcount Sorted Sets Zadd ❯