HyperLogLog

wikipedia:HyperLogLog is an algorithm for the count-distinct problem.

Calculating the exact cardinality of a multiset requires an amount of memory proportional to the cardinality, which is impractical for very large data sets. The HyperLogLog algorithm is able to estimate cardinalities of > 109 with a typical accuracy (standard error) of 2%, using 1.5 kB of memory.

/etc/redis.conf

HyperLogLog++ counts based on the hashes of the values with some properties:

• Configurable precision, which decides on how to trade memory for accuracy
• Excellent accuracy on low-cardinality sets
• Fixed memory usage: no matter if there are tens or billions of unique values, memory usage only depends on the configured precision.

See also

• LogLog
• Redis, installation, /etc/redis.conf, values.yml, Redis Cluster, Redis Sentinel, /etc/redis-sentinel.conf, Redis memory footprint, redis-cli, redis-benchmark, redis-check-aof, redis-check-rdb, redis-sentinel, redis-server, Amazon MemoryDB for Redis, AOF, Redis changelog, Redis Database (RDB), Append Only File (AOF), Redis logs