Details
Description
There were some new functions added recently to add support for Apache DataSketches HLL calculations. These functions purpose is to give an approximate answer for count(distinct) kind of queries.
The newly introduced functions are:
ds_hll_sketch()
ds_hll_estimate()
ds_hll_union()
Related Jiras:
https://issues.apache.org/jira/browse/IMPALA-9632
https://issues.apache.org/jira/browse/IMPALA-9633
We should document these and mark them as experimental features so that users can try out and hopefully give feedback.