This section contains reference documentation for the DISTINCTCOUNTHLL function.
Signature
DISTINCTCOUNTHLLPLUS(colName, log2m)
Usage Examples
DISTINCTCOUNTHLLPLUS considerations
DISTINCTCOUNTHLL()is faster than DISTINCTCOUNT()if data is pre-aggregated at ingestion or aggregated at a server with enough records. This performance improvement increases when comparing large datasets.
If very few records are pre-aggregated, DISTINCTCOUNTHLL()will not be as fast as DISTINCTCOUNT()because the serialized HLL size is larger than sending individual values.
DISTINCTCOUNTHLLPLUS()provides more precise results than DISTINCTCOUNTHLL()with the same performance.
DISTINCTCOUNTSMARTHLL()automatically shifts to HLL when reaching a threshold, and comes with some overhead.
