Redis HyperLogLog is used for calculating the cardinality of a set or non mathematically speaking it is a probabilistic data structure used to count unique values. Basically it is an algorithm that use randomization such that it can provide an approximation of the number of unique elements in a set by just using a constant complexity, and a fixed/small amount of memory footprint. Each key stored in hyperloglog is only about 12 kbytes per key and with a standard error of 0.81%. There is no limit to the number of items you can count in the HyperLogLog Datatype, unless you approach 2^64 items. If you are planning to use some form of unique count, e.g ipadress

Redis HyperLogLog Datatype – Operations

  • PFADD: Adds or updates one or more members to HyperLogLog, Returns 1 if at least 1 HyperLogLog internal register was altered, 0 otherwise O(1)
  • PFCOUNT: Returns the approximated cardinality computed by the HyperLogLog, 0 if the variable does not exist. O(1).
  • PFMERGE: Merge multiple HyperLogLog values into an unique value O(N)

C# code using Redis HyperLogLog Datatype

So this covers the basic usage of Redish HyperLogLog Datatype, in the next blog post I will cover how to use Pub/Sub in Redis.

For the code please visit

For previous Redis topics

  1. Intro to Redis for .NET Developers
  2. Redis for .NET Developer – Connecting with C#
  3. Redis for .NET Developer – String Datatype
  4. Redis for .NET Developer – String Datatype part 2
  5. Redis for .NET Developer – Hash Datatype
  6. Redis for .NET Developer – List Datatype
  7. Redis for .NET Developer – Redis Sets Datatype
  8. Redis for .NET Developer – Redis Sorted Sets Datatype