Cardinality

wikipedia:Cardinality is generally defined as the number of elements in a set.

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.

NRQL

FROM Metric SELECT cardinality(metric.name) SINCE today RAW

• Metrics
• High cardinality
• HyperLogLog, HyperLogLog++
• Infinite set, Multiset

Activities

• Read about cardinality aggregation in Elasticsearch https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-metrics-cardinality-aggregation.html