Introduction to HyperLogLog

If you’ve been keeping up with the newer statistics developments, you might have heard about this new state-of-the-art cardinality estimation algorithm called HyperLogLog.

This technique is now available for PostgreSQL in the extension postgresql-hll available on GitHub and is packaged for multiple operating systems such as Debian and RHEL through the PostgreSQL community packaging efforts and resources.

HyperLogLog is a very special hash value. It aggregates enough information into a single scalar value to compute a distinct value with some precision loss.

Use case: Count unique visitors

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